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On the in-plane properties and capacities of infilled frames
... Position and size of these openings are selected based on the functional requirement of the building. It has been experienced from past earthquakes [1,2], laboratory experiments [3][4][5][6]70,71], and analytical studies [7][8][9][10]46,47,72] that presence of infills in the RC frames have significant influence on the overall seismic response and collapse mechanism of the infilled frame structure. Infills interact with the adjacent RC frame members, and eventually presence of infill in RC frame increases its lateral strength and stiffness, reduces deformability and fundamental time period leading to alteration of seismic demand as compared to its bare frame counterpart [8,11,25,47,76]. ...
... It has been experienced from past earthquakes [1,2], laboratory experiments [3][4][5][6]70,71], and analytical studies [7][8][9][10]46,47,72] that presence of infills in the RC frames have significant influence on the overall seismic response and collapse mechanism of the infilled frame structure. Infills interact with the adjacent RC frame members, and eventually presence of infill in RC frame increases its lateral strength and stiffness, reduces deformability and fundamental time period leading to alteration of seismic demand as compared to its bare frame counterpart [8,11,25,47,76]. Under lateral loading, infills get detached from the unloaded corners and behave as compressive diagonal strut along the loaded corners as shown in Fig. 1. ...
... However, due to intensive computational effort, its use is very limited to actual structures. On the other hand, macro-modeling approaches [46,47,74] are used widely for simulation of infills in order to capture the global response of infilled RC frames with reasonable accuracy. Using equivalent diagonal strut to model infills has received very good appreciation among the researchers for its simplicity to use with minimal computational efforts. ...
Openings provided to meet functional requirements are often neglected in analytical assessment of Un-Reinforced Masonry (URM) infilled Reinforced Concrete (RC) frame buildings, mostly due to unavailability of simplified comprehensive model to simulate its effect. Ignoring presence of opening in infills results unrealistic assessment of seismic response for these popular building typologies, as opening reduces the strength and stiffness of the composite frame. Several reduction factor models have been developed over the years to account effect of opening in infills. In the present study efficacy of five such models of opening have been investigated which can be used by design practitioners for simulation of opening with sufficient accuracy in predicting the response of composite frame. Extensive analytical study has been conducted on a set of mid-rise and high-rise Indian infilled RC frame buildings considering various realistic combinations of openings by varying size, shape of doors and windows. The study revealed that increasing opening in infills significantly affects the seismic performance, and consequent fragility thereby reduces lateral strength, stiffness, ductility, while increasing fundamental time period, overall deformation capacity and damage probability.
... The out-of-plane (OOP) failure of a wall has been studied in the past years, all concluding that this type of failure is more disastrous than the in-plane (IF) failure [4,5]. IP failure is mainly characterized by the combination of several local failures, namely, corner crushing, diagonal compression, frame failure, bedjoint sliding, and diagonal cracking [6][7][8]. Many factors play a role in the mechanical performance of masonry-infilled reinforced concrete (RC) structures. ...
... Many factors play a role in the mechanical performance of masonry-infilled reinforced concrete (RC) structures. Some of these factors include but are not limited to modulus of elasticity, tensile strength, and compressive strength of the infill, the inter-layer strength between masonry blocks (i.e., brick-mortar interface), as well as the mechanical properties of the surrounding RC frame [6,9]. Friction and stiffness between the infill and the interface, their connection and their stiffness relative to one another also play an undeniable role in the IP failure of infilled frames [10]. ...
An experimental study was carried out to contribute to the rather limited data on the out-of-plane (OOP) behavior of masonry infills in reinforced concrete (RC) frames strengthened with the wall post and the textile-reinforced mortar (TRM). For this purpose, one unreinforced specimen served as the control, one specimen was reinforced with the wall post, and two specimens were reinforced with the TRM. They were fabricated and subjected to cyclic OOP loading until a drift ratio of 6%. Load and displacement values were recorded, and the research team discussed the failure mechanisms of the specimens. Results showed that the application of the wall post had the highest efficiency as it increased the load by about 3 times, while this value for TRM-strengthened walls was only 1.5. Strengthening modified the cracking, shifting it towards the middle parts of the wall, changing it from a brittle to a failure mode. Comparison of the envelope curves of specimens revealed significant improvements. The ultimate displacement and energy absorption capacity for the specimen reinforced with the post wall increased by 30% and 300% respectively. Similarly, for TRM-strengthened specimens, these values were 48% and 100%.
... Multi-strut models capture the behavior of infilled frames more precisely and in more detail than single-strut models [57]. Comprehensive reviews on the macroand micro-modeling of infill walls can be found in [70][71][72]. In the present study, to account for the contribution of masonry infill walls in the lateral load-carrying capacity of RC frames, the multi-strut model developed by Saneinejad and Hobbs [49] is utilized. ...
... The accuracy of this model was confirmed by comparing its outcomes with some analytical models, inelastic finite element method data, and test data [49,[73][74][75]. More details related to this model are found in [48,49,72]. The responses of a masonry infill wall specimen tested in Ref. [76] were examined in Ref. [75]. ...
Removing masonry infill walls from the ground or lower stories of buildings to make more open spaces, may lead to forming soft-story structural irregularities. Since considering the masonry infill walls as non-structural components is a common assumption in the evaluation of the seismic demand of buildings, there is a lack of knowledge dealing with the influence of the soft-story effect on the seismic response. In this study, the performance of 4-, 8-, and 12-story moment-resisting reinforced concrete frames with and without a ground soft story is compared first. Then, a proposal including the use of a yielding dissipater device to retrofit soft-story buildings is presented. The low cost, the simple manufacturing technology, and the same behavior in tension and compression, which makes the new axial force not imposed on the columns, are some of the advantages of this device. In order to assess the seismic performance of the proposed system, incremental dynamic analysis was conducted on the frames. Five states were considered for each frame: (a) bare frame, (b) fully-infilled frame, (c) ground soft-story frame, (d) and (e) retrofitted frames with two different configurations of yielding dissipater devices in the ground soft story. The responses of the structures are compared in terms of capacity curves, progressive damage curves, inter-story drifts, and story damage values. The results demonstrate that the frames equipped with the yielding dissipater devices experience higher lateral load capacity, lower overall damage, lower drift, and a lower damage value in the ground story than the soft-story ones.
... The position and size of these apertures are governed by the functional requirements of the building. Previous earthquakes (Jain et al., 2001;Murty et al., 2004), laboratory testing (Al-Chaar et al., 2002;Basha & Kaushik, 2016;Buonopane & White, 1999;Cavaleri & Trapani, 2014;Dhanasekhar & a. P. A. W., 1986;Mehrabi et al., 1996), and analytical studies (Asteris, 2003;Asteris et al., 2011;Chrysostomou & Asteris, 2012;Chrysostomou et al., 2002;El-Dakhakhni et al., 2003;Fardis & Panagiotakos, 1997;Mehrabi & Shing, 1997) have shown that infills in RC frames have a significant impact on the overall seismic response and collapse process of the infilled frame structure. Infills in RC frames interact with the surrounding members, boosting their lateral strength and stiffness while decreasing their elastic modulus and fundamental timespan in contrast to bare frames (Asteris et al., 2015;Chrysostomou & Asteris, 2012;DolSEk ˇ M & Fajfar P., 2008;Fardis & Panagiotakos, 1997;Haldar, 2013). ...
... Previous earthquakes (Jain et al., 2001;Murty et al., 2004), laboratory testing (Al-Chaar et al., 2002;Basha & Kaushik, 2016;Buonopane & White, 1999;Cavaleri & Trapani, 2014;Dhanasekhar & a. P. A. W., 1986;Mehrabi et al., 1996), and analytical studies (Asteris, 2003;Asteris et al., 2011;Chrysostomou & Asteris, 2012;Chrysostomou et al., 2002;El-Dakhakhni et al., 2003;Fardis & Panagiotakos, 1997;Mehrabi & Shing, 1997) have shown that infills in RC frames have a significant impact on the overall seismic response and collapse process of the infilled frame structure. Infills in RC frames interact with the surrounding members, boosting their lateral strength and stiffness while decreasing their elastic modulus and fundamental timespan in contrast to bare frames (Asteris et al., 2015;Chrysostomou & Asteris, 2012;DolSEk ˇ M & Fajfar P., 2008;Fardis & Panagiotakos, 1997;Haldar, 2013). This alters seismic demand. ...
Energy consumption is consecutively increasing nowadays in residential sectors. So as to overcome this issue, window openings are provided in the masonry units. The window openings will diminish the energy consumption in the buildings. The increase in opening size will directly improves the ventilation and enrich in the comfort of the buildings. However, as the size of the window increases, the thermal comfort is improved but, the structural properties of the masonry unit will be diminished. To rectify this current issue, the window opening size has been optimized to improve the structural properties without compromising the thermal aspects. The percentage of window opening sizes are 10%, 20%, 30% up to 100% from the masonry infill area. The window openings are made in single bay single storey reinforced concrete Infilled frame model. The static lateral loading is applied to the RC Infilled frame. A finite element analysis software was used for analysing this issue. By analysing the models, the window opening size of 50% from the masonry infill attains a better performance when comparing all the other models. The soft computing approaches using ANN modelling to predict the Stiffness of the frame. The ANN results indicate R² values of 0.98466 in 0%, 0.9674 in 20%, 0.9762 in 40%, 0.94987 in 60%, 0.95577 in 80% and 0.99421 in 100% in every instance, ANN model is a highly effective prediction of stiffness of the frame with openings. Therefore, the ANN model is the most effective machine-learning algorithm for the stiffness of the frame.
... Under seismic loading conditions, RC frames with relatively low stiffness deflect and activate the much stiffer masonry infills, which results in a complex interaction between the RC frame and infills. This interaction was described and investigated by several authors (Moghaddam and Dowling 1987;Mehrabi et al. 1996;Crisafulli 1997;Chrysostomou and Asteris 2012). ...
... Based on the results of the first experimental studies, Polyakov (1960) and Smith (1966) suggested the idealization of infilled frames as braced frames with diagonal compression struts representing the contribution of the masonry infill. However, the results of numerous studies carried out (Mainstone 1971;Paulay and Priestley 1992;Angel et al. 1994;Mehrabi et al. 1996;Flanagan and Bennett 1999a;Chrysostomou and Asteris 2012) showed that the level of contribution of masonry infills cannot be easily determined as it depends on the specific failure modes of the masonry infill or the surrounding frame. According to Crisafulli (1997) and El-Dakhakhni et al. (2003) the dominant failure modes of masonry infills subjected to in-plane loading are shear failure due to sliding, diagonal tension failure of the bricks along the diagonal compression struts and compression failure of the diagonal compression struts or the corners. ...
Reinforced concrete (RC) frames with masonry infills can be encountered all over the world, especially in earthquake prone regions. Although masonry infills are usually not considered in the design process, in the case of seismic loading they are subjected to in-plane and out-of-plane forces that can act separately or simultaneously. In recent earthquakes it was observed that seismic loads can severely damage masonry infills or even cause their complete collapse, especially when the loads act simultaneously. Due to this, effects of interaction of in-plane and out-of-plane loads on seismic performance of masonry infills have received more attention recently. However, most of studies focus only on fully infilled frames, even though openings, such as windows and doors are essential parts of infills that substantially affect the seismic response of masonry infills. Therefore, this article presents the results of a comprehensive experimental study on nine full-scale traditional masonry RC frames infilled with modern hollow clay bricks for configurations with and without window and door openings under separate, sequential and combined in-plane and out-of-plane loading. Based on the results, a detailed comparison and interpretation for the different infill and loading configurations is presented. The test results clearly show the unfavourable influence of openings and combined loading conditions as well as the importance of the quality of execution of the circumferential mortar joint between infill and frame. The new findings can be used as a basis for the required development of innovative solutions to improve significantly the seismic performance of RC frames with masonry infills.
... Chrysostomou and Asteris studied the in-plane response of infills in 2012 (Chrysostomou & Asteris, 2012). To this end, the required expressions to calculate the stiffness, strength, and deformational capacity of the infills were evaluated for different failure modes using parametric studies. ...
... calculated the width using Eq. (8)-the parameters of which were already defined-as followsChrysostomou and Asteris (2012): ...
In this paper, the results of a comparative study on diagonal strut models are presented to simulate the in-plane behavior of concrete sandwich panels enclosed in a steel frame. After a brief overview of experimental tests on the cyclic in-plane behavior of Concrete Sandwich Panel-Infilled Steel Frames (CSP-ISF), a 2D finite-element model is developed through DIANA software. Then, CSP-ISF structures are modeled using macro-modeling approaches available in the literature and known as the diagonal strut model, to compare the results of the numerical analysis with experimental data. The results show good consistency of Liauw and Kwan model with the experimental response of CSP-ISFs. Finally, modified formulas including reduction factors of the lateral stiffness and ultimate strength are proposed to estimate the in-plane lateral behavior of CSP-ISFs with a central opening, i.e., perforated infilled frames.
... A modelagem foi comparada com resultados experimentais e juntamente com outras, presentes na literatura, concluiu-se que o modelo é capaz de representar o comportamento de quadros preenchidos desde que haja uma fina calibração, em especial dos parâmetros que definem o comportamento histerético da alvenaria. CHRYSOSTOMOU e ASTERIS [6] estudaram a contribuição da alvenaria na resistência das estruturas frente a ações sísmicas. Apresentaram equações para quantificar a rigidez no plano da alvenaria, a resistência e a capacidade de deformação das paredes, bem como métodos simplificados para prever a forma de ruptura. ...
... A autora observou variação de mais de 200% entre as expressões analíticas que determinam a largura da diagonal equivalente para painéis que não possuem aberturas. Concluiu que as formulações que apresentam melhores resultados são as de LIAUW e KWAN [19], DURRANI e LUO [22] e CHRYSOSTOMOU e ASTERIS [6] e que, apesar de ser a mais utilizada, a expressão de MAINSTONE [17] é a que apresenta resultados mais conservadores. ...
The focus of this paper is to evaluate the effects of considering masonry infill walls as resistant elements in concrete structures. Recommendations of the recently updated Brazilian code for the design of structural masonry - ABNT NBR 16868-1 - were included in the analysis of this paper. Expressions presented in the literature and in Brazilian code were used to determine the equivalent diagonal width. Two-dimensional models with the aid of the Finite Element Method (FEM) were used to determine the equivalent diagonal width allowing the comparison with analytical expressions from the literature. The differences were also analyzed in terms of lateral displacements of a multistory reinforced concrete building with concrete masonry infill walls. The simulations were carried out using ANSYS and FTOOL programs. Significant differences between the values of the equivalent diagonal width obtained by the expressions from the literature were observed in all the single-story single-bay frames. Such differences had influence on the lateral displacements of the single-story frames and the multistory building. For the cases analyzed, the expression proposed by Mainstone was the one that led to the best results in comparison to MEF simulations.
Keywords
Participating masonry; Structural analysis; Infill frames
... Due to rigid connection of masonry infill to the surrounding concrete, as a consequence of horizontal load, compressive force is activated in the masonry wall. The paths of compressive forces in the wall mainly follow diagonal path [11][12][13][14]. Above mentioned in-plane forces can cause different failure modes of masonry infill walls, such as infill sliding shear failure, diagonal cracking failure, diagonal compression failure and corner crushing failure [12,14]. ...
... The paths of compressive forces in the wall mainly follow diagonal path [11][12][13][14]. Above mentioned in-plane forces can cause different failure modes of masonry infill walls, such as infill sliding shear failure, diagonal cracking failure, diagonal compression failure and corner crushing failure [12,14]. ...
Reinforced concrete frames with masonry infill walls are popular form of construction all over the world as well in seismic regions. While severe earthquakes can cause high level of damage of both reinforced concrete and masonry infills, earthquakes of lower to medium intensity sometimes can cause significant level of damage of masonry infill walls. Especially important is the level of damage of face loaded infill masonry walls (out-of-plane direction) as out-of-plane load cannot only bring high level of damage to the wall, it can also be life-threating for the people near the wall. The response in out-of-plane direction directly depends on the prior in-plane damage, as previous investigation shown that it decreases resistance capacity of the in-fills. Behaviour of infill masonry walls with and without prior in-plane load is investigated in the experimental campaign and the results are presented in this paper. These results are later compared with analytical approaches for the out-of-plane resistance from the literature. Conclusions based on the experimental campaign on the influence of prior in-plane damage on the out-of-plane response of infill walls are compared with the conclusions from other authors who investigated the same problematic.
... When analyzing the plane frame models, this decrease was between 39.6% and 52.1%. [6] 0.845 0.879 Mainstone [54] 1.001 1.042 Durrani and Luo [53] 0.951 0.975 Liauw and Kwan [56] 0.865 0.895 Decanini and Fantin [57] 0.774 0.825 Paulay and Priestley [58] 0.845 0.879 Chrysostomou and Asteris [59] 0.906 0.933 ...
... Total shear force (kN) Without infill walls 351.20 CSA 304 [6] 551.61 Mainstone [54] 463.77 Durrani and Luo [53] 490.98 Liauw and Kwan [56] 538.01 Decanini and Fantin [57] 599.51 Paulay and Priestley [58] 551.61 Chrysostomou and Asteris [59] 514.74 ...
In this paper, seismic analyses are performed of a reinforced concrete frame building with participating masonry walls are carried out. The spectral method of the Brazilian code – ABNT 15421:2006 – was used to obtain the lateral seismic loads. The equivalent diagonal-strut model was employed to simulate the axial stiffness of the masonry walls in the frames, according to different formulations founded in literature. The main purpose is to evaluate the differences implemented by the different formulations for the equivalent strut on the seismic response. This paper also aims at comparing results obtained when the masonry stiffness is not considered under seismic loads. The results obtained are analyzed with the purpose of providing contributions for structural engineers in the design of framed structure buildings with participating masonry walls subjected to seismic loads.
... Kako bi se koristila pritisnuta dijagonala za predstavljanje ispune, karakteristike kao što su širina dijagonale, krutost i veza sila-pomeranje moraju se definisati. Neki autori [29,41,48] definisali su širinu dijagonale kao procenat dužine dijagonale, dok su drugi [49][50][51][52][53][54] zaključili da The equivalent diagonal strut approach can model the global force-displacement behaviour of the infilled frame, but model of the infill wall with just one single strut element is incapable of properly taking into account the change in the bending moment and shear diagram along the column length due to the presence of the panel [43] and therefore it is ineffective in modelling the complex behaviour of infilled frames as reported in [44]. To overpass this limit, several researchers [45][46][47] developed models with different orientations and number of struts. ...
... U ovom pristupu bitno je obezbediti adekvatnu vezu okvira i ispune koja može da prihvati opterećenje van ravni kako se zid ispune ne bi srušio. Za ovu svrhu, veza ispune i others [49][50][51][52][53][54] found that effective width is dependent on the length of contact between the infill and the frame and relative panel to frame stiffness parameter, λh, defined by [55]. ...
Reinforced concrete (RC) buildings with masonry infill walls are widely used in many countries all over the world. Although infills are considered as non-structural elements, they significantly change dynamic characteristics of RC frame structures during earthquake excitation. Recently, significant effort was spent on studying decoupled infills, which are isolated from the surrounding frame usually by adding a gap between frame and infill. In this case, the frame deformation does not activate infill wall, thus infills are not influencing the behaviour of the frame. This paper presents the results of the investigation of the behaviour of RC frame buildings with the INODIS system that decouples masonry infills from the surrounding frame. Effect of masonry infill decoupling was investigated first on the one-bay one-storey frame. This was used as a base for parametric study on the frames with more bays and storeys, as well as on the building level. Change of stiffness and dynamic characteristics was analysed as well as response under earthquake loading. Comparison with the bare frame and traditionally infilled frame was performed. The results show that behaviour of the decoupled infilled frames is similar to the bare frame, whereas behaviour of frames with traditional infills is significantly different and demands complex numerical models. This means that if adequate decoupling is applied, design of infilled frame buildings can be significantly simplified.
... Macro-modelling of infilled frames is well-studied and exhaustive review papers on compressive strut-models can be found [43,[45][46][47][48][49][50]. The principle of strut-models is that compressive strain is developed in the diagonal of the infill due to the flexural deformation of the surrounding RC members when increasing in-plane displacements are applied to the frame [51]. ...
... A number of analytical expressions exist for the definition of the strut parameters for macro-modelling masonry infills [e.g.: [58][59][60][61]. The empirical Eq. (10) for the equivalent strut width (w) by Mainstone [58,62] is widely accepted [e.g.: 45,48,63] and is also used here: ...
Non-structural masonry infills in existing reinforced concrete (RC) frame structures are known to affect their seismic behaviour significantly with potential detrimental effects. Increasing experimental evidence is available for the use of composite materials, such as fibre-reinforced polymers (FRP) and textile reinforced mortars (TRM), for in-plane retrofitting of brittle masonry infills. In order to apply such strengthening solutions in practice, adequate analytical models for predicting the behaviour are needed, however the large variation in infill properties already makes modelling the behaviour of non-retrofitted infills a challenge. Based on existing experimental and numerical studies on retrofitted infills, a macro-model is proposed, comprising a tie to account for the tensile strength of the composites materials, but also an increased compressive strut width due to the composite materials improving connection of the infill to the frame. After compiling a database of experimental data for composite retrofitted specimens tested in the literature, empirical equations for tie and strut strength was obtained. These equations constitute the first unified approach for FRP- and TRM-strengthened infills and were verified against the largest database of experimental results to date. The strut model was calibrated for the increase in strut width in terms of experimentally obtained stiffness increase, while the tie model was determined based on the remaining increase in strength. The empirical equations were shown to achieve a relatively high correlation with experimental results and to represent the mechanics of tested specimens well in terms of observed damage, hence indicating their potential for use as design-oriented equations for composite strengthened infills.
... In a seismic event, however, they carry inplane shear loads or out-of-plane flexural loads [13,14]. Past earthquakes showed that the out-of-plane failures are more disastrous than the in-plane ones [15][16][17]. Most of the previous studies categorized the failure modes of masonryinfilled frames into five distinct modes such as frame failure, sliding shear, diagonal compression, corner crushing, and diagonal cracking failure [17]. ...
... Past earthquakes showed that the out-of-plane failures are more disastrous than the in-plane ones [15][16][17]. Most of the previous studies categorized the failure modes of masonryinfilled frames into five distinct modes such as frame failure, sliding shear, diagonal compression, corner crushing, and diagonal cracking failure [17]. ...
A numerical study was conducted to investigate the in-plane behavior of a masonry-infilled reinforced concrete (RC) frame retrofitted with textile-reinforced mortar (TRM). A two-dimensional finite element model was developed using DIANA finite element analysis (FEA) software to simulate the 2 : 3 scaled three-storey masonry-infilled RC frame retrofitted with TRM that was studied experimentally in the past. The three-storey structure used in the test was with a nonseismic design and detailing, and was subjected to in-plane displacement-control cyclic loading. The current study evaluates the capabilities of a representative numerical model to simulate the results of the experimental test, and after the calibration of the numerical model sensitivity analysis and parametric study were performed. In order to create an accurate numerical model, suitable constitutive models, based on the smeared crack approach, were used to characterize the nonlinear response of concrete, masonry infill, and TRM. The calibration of the models was based on the experimental results or inverse fitting based on optimizing the simulation of the response. The numerical model proved capable of simulating the in-plane behavior of the retrofitted masonry-infilled RC frame with good accuracy in terms of initial stiffness, and its deterioration, shear capacity, and cracking patterns. The calibrated model was then used to perform sensitivity analysis in order to examine the influence of infill-frame interface properties (tangential and normal stiffness) on the behavior of the retrofitted infilled frame. The numerical results showed that the gap opening is influenced significantly by the stiffness of the interface. In addition, a parametric study was performed in order to evaluate the importance of the full-bond condition between the TRM and the masonry-infilled RC frame. The numerical results indicate that the composite action between the TRM and the masonry-infilled RC frame improves the global stiffness and lateral resistance of the infilled frame, and it reduces the gap opening between the masonry infill and the RC frame.
1. Introduction
Masonry-infilled RC frame structures are widely dispersed around the world, and most of them are located in the seismic region while they were built before the development of new seismic design codes. Therefore, seismic retrofitting of existing masonry structures is nowadays a challenging engineering problem, since the most significant seismic risk in the world today is associated with existing buildings. Several rehabilitation techniques have been developed over the years [1, 2] in order to improve the performance of masonry-infilled RC frame structures. Masonry infills are usually treated as a nonstructural element, and their interaction with the bounding frame is ignored in the design. This interaction may or may not be beneficial to the performance of the structure [3, 4]. For instance, the existence of masonry infill in an RC frame can increase the strength, stiffness, and lateral capacity of the building [5–7]. On the contrary, the existence of masonry infill can introduce brittle shear failure mechanisms associated with the wall-frame interaction [8]. The irregularities of infill in plan and elevation cause different types of failure mechanisms due to large concentration demand in a few members of the structure. The most typical failure mechanisms are the soft-storey mechanism [9] where the stiffness at the lower floor is smaller than the stiffness at the storey above, the short-column mechanism [10] where the infill wall in the RC frame is shorter than the column height, and plan torsion effect where the infills are located in the plan asymmetrically [11, 12]. The failure mechanism and the load resistance of the masonry-infilled RC frame depend on a number of parameters such as geometry of the wall (height/width ratio and openings), geometrical plane and elevation distribution of the infills in a structure, quality of the materials, stiffness and ductility of the frame, type of loading, detailing, relative infill-frame stiffness and strength, and quality of the workmanship. In a seismic event, however, they carry in-plane shear loads or out-of-plane flexural loads [13, 14]. Past earthquakes showed that the out-of-plane failures are more disastrous than the in-plane ones [15–17]. Most of the previous studies categorized the failure modes of masonry-infilled frames into five distinct modes such as frame failure, sliding shear, diagonal compression, corner crushing, and diagonal cracking failure [17].
Retrofit or repair structures built before any provision for an earthquake is one of the most serious problems faced by the engineers today. Several rehabilitation techniques have been developed over the years so that the masonry-infilled frame structures can be enhanced to satisfy modern seismic design codes [1, 2]. Amongst them, fiber-reinforced polymers (FRP) [18–22] have received extensive attention in the recent years due to their high mechanical strength and ease of application. The use of ductile fiber-reinforced cementitious matrix composites (FRCM) [23, 24] has recently received attention as a sustainable, and more compatible solution for retrofitting concrete structures compared to the traditional method of concrete jacketing. Owing to the need for introducing innovative materials, more recently, the research community has focused on the use of textile-reinforced mortar (TRM) for retrofitting the masonry and cultural heritage structures. TRM is a composite material consistingof inorganic matrix (lime-based or cement-based) and the fiber reinforcing textile. The variety of fibers and mortar type leads to a wide range of possible mechanical properties for the TRM. The use of the inorganic matrix instead of epoxy resins as in the case of FRPs overcomes some of their drawbacks [25, 26]. The information regarding the effectiveness of TRM in retrofitting masonry infills under static monotonic and cyclic loading is still very limited [27–33]. Papanicolaοu et al. [34, 35] concluded that TRM jacketing is an extremely promising solution for retrofitting masonry walls subjected to either out-of-plane or in-plane loading. Particularly, it was stated that TRM confining jackets provide an increase in compressive strength and deformation capacity of the masonry wall. Bernat et al. [36, 37] carried out a study aiming at investigating the influence of three different types of mortar, two different types of fiber (glass and carbon grids), and the possible benefit of using anchors to improve the connection between the walls and the external reinforcement on the performance of masonry walls retrofitted with the TRM. The results showed that the application of TRM provides 100% increase in the initial load-bearing capacity of the wall under an eccentric axial load. Moreover, a stiffer and more homogeneous behavior is noticed when TRM is applied. Later, Koutas et al. [31, 32] performed an experimental and numerical study to investigate the behavior of TRM-retrofitted masonry-infilled RC frames under cyclic loading. The study showed that in the retrofitted specimen, an approximately 56% increase in the lateral strength, accompanied by a 52% higher deformation capacity at the top of the structure at the ultimate strength state compared to the unretrofitted one. In addition, the retrofitted specimen dissipated 22.5% more energy compared to the unretrofitted one, for the same loading history. Recently, Akhoundi et al. [38] studied the performance of TRM-retrofitted masonry-infilled RC frames using two half-scale specimens subjected to in-plane cyclic loading. A similar application of the TRM retrofitting technique to that of Koutas et al. [31, 32] was used. Based on their results, retrofitting of masonry infills and connecting them to the RC frame by simply extending the retrofitting layers to the faces of the columns and the beam yielded an increase in lateral stiffness and ultimate strength of about 40%. Koutas et al. [26] presented an overview of studies which used the TRM for flexural and shear confinement of RC structures and for seismic retrofitting of masonry structures, while the key parameters of each study were examined. The authors concluded that the TRM technique was highly effective in increasing load-carrying capacity and the stiffness of columns, beams, and the infill walls.
Numerical studies aiming for predicting the behavior of retrofitted masonry infill wall are limited and most of them used the macromodelling approach and focused on the simulation of the behaviour of TRM-retrofitted masonry infill wall under monotonic loading. Koutas et al. [32] proposed a macromodel using a single strut to represent the infill panel to capture the in-plane response of masonry-infilled RC frame retrofitted with TRM. Other studies also proposed macromodelling techniques to study the effectiveness of the TRM retrofitting method on the behavior of the masonry infill wall under monotonic loading [39, 40]. On the contrary, several numerical studies were conducted to investigate the effectiveness of FRP on the in-plane and out-of-plane behavior of the masonry-infilled RC frame [41, 42]. In addition, detailed micromodels have been developed to simulate the behavior of TRM-retrofitted masonry walls, using a microscopic smeared crack approach for modelling the masonry wall, while pushover analyses were performed for these models [39, 43, 44]. Only one study can be found in the literature concerning detailed numerical modelling of retrofitted masonry wall at a structural level, which focuses on the static monotonic nonlinear response of the TRM-masonry infill [45]. It is important to note that a number of numerical studies using a macromodelling approach have been performed in order to investigate the influence of masonry infills (with and without openings) on the structural capacity of the RC frame structure [46–48]. Numerical modelling of masonry-infilled structures retrofitted with TRM is a complex task due to the combination of many materials governed by very different constitutive relationships resulting in a complex response but comprises a vital step towards understanding the parameters that influence the performance of retrofitted structures and evaluating the effectiveness of this technique in greater depth.
Focusing on the numerical modelling of masonry-infilled frame structures retrofitted with TRM, initially, an efficient technique for modelling the behavior of masonry infill is chosen, followed by the determination of adequate constitutive models for each component of the structural system. In the literature, different modelling techniques that simulate the behavior of the infill wall can be found and can divided into three categories [49, 50] as follows: detailed or simplified micromodelling approach, where the bricks, mortar, and the interface between them are modelled separately by continuum elements or the bricks are modeled by continumm elements and the interaction between brick units and mortar with interface elements with an effective thickness [51–53], macromodelling where the bricks and mortar are modeled by a continumm element or the infill wall is represented by a diagonal equivalent strut (or multiple diagonal) element which is described by a constitutive nonlinear monotonic or cyclic law [54–59], and mesomodelling which combines the advantages of the abovementioned models such as computational efficiency of the macromodel and numerical accuracy of micromodels [50]. In the mesomodelling approach, the masonry infill walls are modelled using continuous elements and the interaction between brick units and mortar is taken into account, the possible failure in tension and shear [60].
This paper presents a numerical model that represents the in-plane behavior of a three-storey TRM-retrofitted masonry-infilled RC frame under cyclic loading, following the mesomodelling approach to simulate the masonry infill wall. A two-dimensional FE model was developed in the DIANA FEA software, and a eigenvalue analysis, followed by a nonlinear displacement-based cyclic analysis was performed to simulate the experimental test conducted by Koutas et al. [31]. The three-storey structure used in the experimental test was with a nonseismic design and detailing and it was subjected to in-plane cyclic loading. The current study evaluates the capabilities of a representative numerical model to simulate the results of the experimental test and investigates some of the parameters that are able to affect the behavior of masonry-infilled RC frames retrofitted with TRM through sensitivity analysis and parametric study. In order to create an accurate numerical model, suitable constitutive models, based on the smeared crack approach, were used to characterize the nonlinear response of concrete, masonry infill, and TRM. The calibration of the models was based on the experimental results or inverse fitting based on optimizing the simulation of the response. The numerical model proved to be capable of simulating the in-plane behavior of the retrofitted masonry-infilled RC frame with good accuracy in terms of initial stiffness, and its deterioration, shear capacity, and cracking patterns. Sensitivity analysis was performed in order to examine the influence of infill-frame interface properties (tangential and normal stiffness) on the behaviour of the retrofitted infilled frame. The numerical results showed that the gap opening is influenced significantly by the stiffness of the infill-frame interface. In addition, a parametric study was performed in order to evaluate the importance of the full-bond condition between the TRM and the masonry-infilled RC frame. The numerical results indicate that composite action between the TRM and the masonry-infilled RC frame improves the global stiffness and lateral resistance of the infilled frame, and it reduces the gap opening between the masonry infill and the RC frame.
2. Brief Review of the Experimental Test
Koutas et al. [31] performed an experimental study to investigate the effectiveness of the TRM technique for retrofitting a 2 : 3 scaled three-storey masonry-infilled RC frame with nonseismic design and detailing under in-plane cyclic loading. Two masonry-infilled frames were designed and built with and without TRM. In this section, a short description of the experimental case study is presented for the benefit of the reader. Full details about the case study can be found in Koutas et al. [31].
Figure 1(a) shows the geometry of the masonry-infilled RC frame specimen. The C16/20 class of concrete (according to Eurocode (2)) was used for columns (rectangular cross section) and for beams (T-section). The modulus of elasticity and the compressive strength of concrete were 24.1 GPa and 27.8 MPa, respectively. The longitudinal ribbed reinforcement had 12 mm diameter and mean yield stress equal to 550 MPa, while smooth steel stirrups with a mean value of yield stress equal to 270 MPa were used as transverse reinforcement for all concrete members. Perforated, fired clay bricks were used for the construction of masonry infill, while the perforation of the brick was running parallel to the unit’s length in the x-direction. The modulus of elasticity of the masonry infill wall perpendicular to the bed joints and the compressive strength were equal to 3.37 GPa and 5.1 MPa, respectively. The mean value of the shear modulus was 1.38 GPa, while the value of diagonal cracking strength of masonry infill ranges from 0.30 to 0.8 MPa. As shown in Figure 1(a), the masonry infill wall was supported rigidly by the foundation RC beam plate at the bottom of the frame. In addition, Figure 1(b) presents the TRM strengthening scheme for the retrofitted specimen. Glass TRM externally bonded on the face of the masonry wall was used (due to its limited width, the textile was applied with an overlap of about 300 mm along the entire length of each bay, near the bottom part of each storey), and six and eight anchors (the straight part of it was inserted into predrilled holes filled with injected epoxy resin and the fanned parts are bonded by hand pressure on the top of the first TRM layer) were placed along the beam-infill interface of the first and the second floors, respectively, as shown in Figure 1(b). At the ends of RC columns, carbon TRM was used. Commercial fiber-reinforced cement-based mortar was used for TRM with compressive and flexural strength equal to 18.9 and 4.3 MPa, respectively. In addition, the modulus of elasticity of carbon and glass textile was 225 GPa and 73 GPa, respectively, while their tensile strength per running meter was equal to 157 kN/m and 115 kN/m, respectively.
(a)
... The failure mechanisms of masonry-infilled RC frame structures are very complicated because many parameters affect the seismic response, such as material properties, geometric distribution, the relative stiffness between the frames and infill walls, etc. Scholars have summarized and classified the failure modes of the masonry-infilled RC frame structures into five damage modes: (a) sliding shear, (b) diagonal compression, (c) corner crushing, (d) diagonal cracking, and (e) frame failure mode (Merhabi et al. 1996;Crisafulli 1997;Shing and Mehrabi 2002;Asteris et al. 2011;Chrysostomou and Asteris 2012). There is interaction between infill walls and frames, but some seismic survey reports indicate that the infill walls are regarded as non-structural members in the design. ...
The seismic performance of masonry-infilled reinforce concrete (RC) frame buildings is an intricate issue due to the variety and complexity failure mechanisms observed on this type of buildings during an earthquake, mainly due to wall-frame interaction. This leads to seriously damaged infill walls and it can produce large economic losses and even jeopardize human lives in an earthquake event. For this reason, in this study a new type of flexible connection able to reduce the wall-frame interaction, and consequently improving the overall seismic performance of the structure is examined. The research encompasses both experimental and numerical analyses of three distinct cases: a rigid connection (Case 1), a traditionally flexible connection (Case 2), and the new proposed type of flexible connection (Case 3). The in-plane and out-of-plane seismic performance is analyzed and compared for these cases. As a result of the study, the new type of flexible connection effectively reduced in-plane damage of the infill walls and minimized undesirable infill-frame interaction. Compared with rigid and traditional connections, the energy dissipation capacity increased by 37.7% and 3.5% for the masonry-infilled RC frame structure with a new flexible connection. At the same time, the out-of-plane strength and stiffness of the new flexible connection increased by 119.8% and 104.2% in the same prior in-plane drift ratio than that of traditional flexible connection. It is concluded that the steel cable structure (the U-bars are connected to the frames to ensure out-of-plane stability of infill walls.) can improve the restraint of frames on infill walls, which is beneficial to development of out-of-plane horizontal arch mechanism.
... A good state-of-the-art review on the mathematical macro-modeling of solid masonry infilled frames has been presented by Asteris et al. [41]. Chrysostomou and Asteris [42] investigated comprehensively various analytical macro-models for determining the in-plane properties and failure modes of solid infill panels. ...
... In the second group, the damage within the infill is considered, occasionally referring to the initial cracking stage of the panel. The relationships are also sometimes adjusted to represent the fully damaged state [48,49]. Numerous studies [9,45] demonstrate that using one of the proposed equations for equivalent diagonal strut width from literature can provide reasonable outcomes. ...
This study aims to assess the nonlinear behavior of reinforced concrete (RC) structural systems having irregular configurations of unreinforced masonry (URM) infill walls. For the simulation of the infill walls, the equivalent diagonal strut approach proposed in the literature was used for simplicity. The backbone curve of the diagonal struts has been derived based on the existing ones with slight modifications and validated with the test data of four different experimental programs to determine the monotonic response behavioral characteristics of the URM-infilled structures. The simplified strut backbone curve is found to be a feasible candidate to capture the strength and stiffness parameters of the URM walls with reasonable accuracy. Following the validation of the simplified model, three different building models are created to investigate the response of the RC structural systems with different infill wall configurations in the plans and along the elevations using the mode superposition method. It has been concluded that the irregular distribution of the infill walls may result in severe torsional effects and stiffness irregularities for buildings, which may lead to significant damage or even collapse in a building. The capacity curves of each case where the nonlinear static analysis method is applicable have been further reported. It is highlighted that the non-uniform presence of the URM walls has an undesirable impact on the monotonic responses of the structural systems. In this respect, numerous remarks regarding the modeling of infill walls are finally reported for code provisions and engineering practice.
... The influence of an infill wall on the strength, stiffness, ductility, and dynamic characteristics of a reinforced concrete frame was experimentally investigated [10]. The interaction between an infill wall and a boundary frame was studied [11]. Asteris et al. [12] studied an infilled reinforced concrete frame under a lateral load and also investigated a numerical model of the out-of-plane response of a frame with infill walls [13]. ...
The bundled lipped channel–concrete (BLC-C) composite wall structure is a new structure with several advantages such as a high bearing capacity and good seismic performance. However, interface cracks between a BLC-C composite wall and the infill wall (non-structural wall) are a severe problem and need to be urgently resolved. Interface cracks affect not only the esthetics, but also the normal use of a building. The presence of interface cracks changes the perceptions of the owners of a structure, forcing them to question its safety and even take legal action against its developer. Therefore, in this study we aimed to investigate the initial cracking of the interface between a BLC-C composite wall and an infill wall. Unidirectional horizontal loading tests were conducted on two infill wall specimens constrained by BLC-C composite walls on both sides. The finite element analysis software ANSYS was used to simulate the loading process of the tests. The test results were compared to verify the accuracy of the finite element model. A finite element analysis was conducted to determine the effect of the horizontal displacement of the specimens when the interface initially cracked under different parameters such as the widths of the BLC-C composite wall, infill wall, and opening as well as the strength grade of the bricks and maximum normal contact stress. The results showed that a decrease in the width of the BLC-C composite wall or a rise in the width of the infill wall delayed the appearance of interface cracks. A large opening also delayed the occurrence of interface cracks. An enhancement in the strength grade of the bricks led to an earlier appearance of interface cracks. Interface cracks occurred later with an increase in the maximum normal contact stress between the BLC-C composite wall and the infill wall.
... One of the key parameters on the classic ESM is the width of the equivalent strut, which can be calculated by analytical expressions proposed by different authors, as: Mainstone [23], Liauw and Kwan [24], Decanini and Fantin [25], Paulay and Priestley [26], Durrani and Luo [27], Chrysostomou and Asteris [28] and Montandon [8]. ...
... A lot of experimental work has been done to study the behavior of RC infill walls and their interaction with the surrounding frames (Chrysostomou and Asteris, 2012). Until the beginning of the 1900s, most of the researchers studied the behavior of infilling walls under monotonic or cyclic loading, and only a few subjected model structures to dynamic loads such as (Yanev Bojidar., 1979), as well as (Chrysostomou, 1991). ...
The seismic retrofitting of existing multi-storey multi-bay reinforced concrete (RC) frame buildings by the conversion of selected bays into new RC infilled walls is the subject of this research work. The parametric study of the contribution of dowels that connect a new RC infill wall to the surrounding RC frame members was performed through nonlinear dynamic analyses of a numerical finite element (FE) model. The FE model was simulated in DIANA finite element analysis (FEA) software in order to study the effectiveness of the seismic retrofitting of existing structures with the conversion of selected bays into new infilled RC walls for the retrofitting of a multi-storey multi-bay RC frame building. A two-dimensional (2D) frame was modeled, and nonlinear transient analyses were performed to calibrate it using the experimental results obtained from a full-scale experiment found in the literature. The description of the experimental results and of the FE model simulation of the test specimen is provided along with a comparison between the experimental results and the numerical ones. Based on the preliminary results it was concluded that the number of dowels used in the experiment resulted in a monolithic behavior of the RC infilled frame. In order to complement the experimental results and to study the interaction between RC infills and the bounding frame both at the global and local level, numerical simulation experiments were performed by reducing the number of dowels starting from a spacing of 100mm (monolithic) to no dowels. For each scenario, nonlinear response-history analysis was performed and an evaluation of the numerical results of each of these scenarios was subsequently performed. The parametric study of the number of dowels connecting the wall to the bounding frame is presented and conclusions are drawn. The parametric results provide a basis for the development of a general model for the design of RC infills in existing RC frames, particularly regarding the connection details of the new RC infill walls to the existing bounding frame.
... On the other hand, it has been recognized that the infill mainly experiences a compression along the diagonal direction under lateral loads. Polyakov (1960) proposed an idea that using an equivalent diagonal strut to represent the infill, which is deemed as a macromodelling approach to consider the infill effects (Asteris et al. 2011;Crisafulli et al. 2000;Di Trapani et al. 2015) and has been used in the in-plane structural response (e.g., Cavaleri et al. 2017;Chrysostomou and Asteris 2012;Gentile et al. 2019;Perrone et al. 2017) and the coupled in-plane and out-of-plane response (e.g., Di Trapani et al. 2018b;Furtado et al. 2016b) analyses. In the macro-modelling approach (i.e., the diagonal strut model), the critical parameter is the determination of the strut width, and different researchers proposed different formulas to calculate the strut width (Klingner and Bertero 1978;Liauw and Kwan 1984;Mainstone 1971). ...
The seismic behaviour of masonry infilled frames has attracted extensive attention from researchers, and it was found that infills normally experienced a diagonal compression under lateral loading. The infill was therefore assumed as an equivalent diagonal strut in structural response estimations of infilled frames, and a force–displacement curve was adopted to describe the mechanical properties of the strut. However, in the development of the force–displacement relationship of infills, the influences of infill aspect ratio, vertical load acting on the surrounding frames, and opening were not systematically addressed. In the present study, detailed three-dimensional finite element models of masonry infilled hinged steel frames are developed in ABAQUS, and a wide parametric study is carried out to investigate the effects of aspect ratio, vertical load, and opening size and location on the lateral stiffness and strength of infill walls. A generalized force–displacement relationship model of infill walls is proposed based on regression analyses of numerical results. The efficacy of the proposed model is examined by using the existing experimental test results, and it shows that the model can accurately predict the lateral stiffness and load-carrying capacity of infill walls and thus has great potential applications in structural designs and analyses for masonry infilled steel frames.
... Masonry constructions are typically complex structures that require a thorough and detailed knowledge and information concerning the mechanical behaviour of their structural systems [40]. This is mainly related to the difficulty in estimating properties, composite and anisotropic nature of the material "masonry" [116,79,87,12,43,13,15]. Practice, as well as experimental testing, has shown that these structures have low resistance in tension and in shear, whereas their compressive strength is, in general, adequate for the level of loads of conventional structures. ...
Masonry is a building material that has been used in the last 10.000 years and remains competitive today for the building industry. The compressive strength of masonry is used in modern design not only for gravitational and lateral loading, but also for quality control of materials and execution. Given the large variations of geometry of units and joint thickness, materials and building practices, it is not feasible to test all possible combinations. Many researchers tried to provide relations to estimate the compressive strength of masonry from the constituents, which remains a challenge. Similarly, modern design codes provide lower bound solutions, which have been demonstrated to be weakly correlated to observed test results in many cases. The present paper adopts soft-computing techniques to address this problem and a dataset with 401 specimens is considered. The obtained results allow to identify the most relevant parameters affecting masonry compressive strength, areas in which more experimental research is needed and expressions providing better estimates when compared to formulas existing in codes or literature.
... However, this should not be surprising, since predictions from different literature models (e.g. equivalent strut models) lead to results which are many times conflicting, raising doubts on their reliability (Chrysostomou and Asteris 2012;Uva et al. 2012;Pasca et al. 2017;Liberatore et al. 2018;De Risi et al. 2018). This apparent incongruence is indeed strongly justified by the different the capacity of these model to account for alternative potential failure mechanisms (e.g. ...
Equivalent strut macro-models are largely employed in research and practice, to reproduce the effect of infill walls in frame structures. These models are simple and at the same time computationally effective, but because of their phenomenological nature, have the big commitment to summarize a complex mechanical interaction with a relatively simple analytical relationship. Because of this, the overall inelastic response of an infilled frame is quite sensitive to that adopted for the equivalent strut. Most of literature models make use of mechanical approaches to define the equivalent strut force–displacement response but, given the large uncertainty in predicting collapse modes actually occurring, results from these models are many times conflicting and raise doubts on their reliability. Based on the limitations of mechanics-based models, this paper proposes a new quadri-linear empirical force–displacement relationship to be used for the equivalent struts. The model definition follows a data-driven approach rather than a mechanical one, therefore parameters defining the force–displacement curve are analytically evaluable by means of empirical correlations. The analytical correlations are derived from an experimental data-set augmented with data obtained data from additional numerical simulations by a refined finite element model. Blind validation tests of the model are carried against six experimental tests not previously included in the data-set definition. A reliability comparison between mechanics-based models and empirical models is finally presented and discussed.
... Despite the extensive work of various researchers (Chrysostomou and Asteris, 2012;Varadharajan et al., 2014a;Varadharajan et al., 2014b;Zameeruddin et al., 2021) the vertical irregularity and cross bracing are partially neglected in the calculation of time period. Various researchers have proposed the equation for estimating the time period of concrete frame structures with vertical irregularity. ...
Regression tree, random forest, bagging and gradient boosting regression-based modelling techniques were used to estimate the time period of precast concrete frame structures with vertical irregularity and cross-bracing using 756 Etabs models. This paper thoroughly explored the efficacy of random forest, regression tree, bagging, gradient boosting-based modelling using RStudio. The time period has been the output parameter while the number of cross-bracing, column size, beam size, soft storey, irregularity coefficient and height of the building has been assigned as input parameters. The accuracy of machine learning techniques has been checked by reference to the formulas published in the literature. A comparison of results indicates that the gradient boosting-based regression approach performed well as compared to random forest regression, bagging and regression tree.
... These approaches can be summarized in three main families, which are simplistic models (macro-models) [1][2][3], average models (meso-models) [3][4][5][6][7], as well as precise models (micromodels) [1][2][3][4][5][8][9][10]. To highlight evidence of this diversity, we can say that it results from the different characteristics of the different components of these masonry walls without forgetting the interaction between them and the surrounding environment [3][4][5][11][12][13]. ...
The multiple earthquakes have proved the effect of chained masonry walls on the seismic behaviour of multistorey reinforced concrete buildings. The chained masonry walls have been considered one of the types of masonry infill walls but without gaps between the wall and the surrounding frame. This participation came intending to study this effect through the modeling of several two-dimensional frames for a multistorey reinforced concrete building, taking into account the hollow brick walls, which represent the most common type in Algeria. We analyzed the proposed models using ETABS finite element software, relying on the response spectrum method and respecting the most important requirements according to the applicable Algerian Seismic Code. After analysis of the different models, the results have been compared according to the parameters of the period, base shear, lateral displacement, and stiffness. Through a critical synthesis of the results, we concluded that these walls could significantly affect the seismic behaviour of this type of buildings. Moreover, the neglect of these walls in the modeling process can lead designers to have a false perception of the behaviour of these buildings towards seismic loadings.
... Despite the complexity, the research in the field of MIF had begun as early as 1930s and continues to evolve for the reasons stated in Table 1. Table 1: Comments from past researchers on analysing MIF Blackard et al. (2009) MIF is a complex and composite structure to model Asteris et al. (2011) MIF does not have the simplicity and accuracy necessary for design engineers Chrysostomou and Asteris (2012) Uncertainties in defining strength properties and modelling exist in both with and without openings in MIF Sipos et al. (2013) Conflicting views of MIF modelling have resulted in the 'deconstruction' of the masonry-infill structures Sigmund and Penava (2014) While some researchers showed that infill walls led to the failure of the building, others have suggested that the walls were beneficial Huang et al. (2016) The interaction between the frame and the wall is complicated Mohyeddin et al. (2017) There cannot be a single model to represent MIF; instead the models need to vary from one structure to the other Alwashali et al. (2019) Large variations in the literature and codes cause confusion to practicing engineers Madiawati et al. (2019) The response of MIF is highly nonlinear Wijaya et al. (2020) Further studies are required to provide clear guidelines on analysing MIF ...
This paper presents a review of the literature on masonry-infilled frame structures subjected to lateral loads. A database of 167 experimental studies on the parameters that influence the response of masonry infill are first discussed. It is shown that there are far too many geometrical and material parameters that affect the behaviour and that the experimental results are not consistent. Masonry infill is in general analysed using an equivalent strut modelling method, which is also briefly described. It is demonstrated that despite rigorous studies across many years, researchers have not been able to find a generic model. Finally, finite element concepts introduced by different researchers are discussed which confirm that further research is required to obtain realistic structural performance of masonry-infilled frames. A future research direction is also provided.
... Therefore, the understanding of the behaviour of this type of structure seems to be very important, particularly under seismic loads. Several published experimental tests [1][2][3][4][5][6][7][8] and numerical investigations [9][10][11][12][13] have proved that the presence of masonry panel in the reinforced concrete frames strongly increases the strength, the lateral stiffness, and the dissipative energy capacity of structures but it could negatively affect the overall behaviour of weak frames. An increase in research studies observed over the last two decades reflects the great attention devoted to understanding the interaction between masonry and the surrounding RC frames [14]. ...
Performance evaluation of masonry Infilled RC frame structures under lateral loads Numerous studies on masonry infill panels have greatly contributed to the research of strength, stiffness and energy dissipation capacity of various buildings. If the effects of masonry panels are disregarded, structural damage will occur under any significant ground motion, and even lead to collapse of the entire structure. The mode of failure is strongly dependent on the masonry and RC frame interaction. This work proposes an evaluation method for determining the participation ratio of masonry infill panels on RC frames under lateral loads.
... Brick masonry infill wall is modelled as a single strut. Various expressions for strut width calculation have been proposed by Holmes [6], Mainstone [7], Decanini and Fantin [8], Paulay and Priestley [9], Liaw and Kwan [10], Durrani and Luo [11], Chrysostomou and Asteris [12]. Following Mainstone (1971) expression which has been adopted in IS 1893 (Part 1) : 2016 for strut width calculation. ...
Open ground storey buildings are quite popular in India due to availability of parking space and high commercial value of the land. However, these open ground storey buildings become first victims during earthquake ground shaking. The same is evident from the collapse and huge damage in ground story columns during past earthquake events. This led to a huge loss of life and property. Hence, there is an urgent need to take up retrofit activities of open ground storey buildings. There were some instances where retrofit activities were taken up on open ground story buildings. However, the performance of the building was not tested after ground storey retrofit. To build confidence among the general public, there is a need to demonstrate that the retrofitted buildings not only save lives but also resist earthquake with minimum damage. This paper is an attempt to demonstrate the same. In this paper, a case study of G+5 open ground storey building has been taken and nonlinear static pushover analysis (POA) is performed to obtain capacity curve. Later, the building is retrofitted in its ground/first storey and again capacity curve is obtained using the POA. It is found that the performance of the building significantly improved. However, from the hinge formation pattern, it is observed that the damage has propagated to the second storey. To improve the performance further, the second storey is also retrofitted and POA is performed again. Further, as per the damage propagation to upper stories, retrofitting is done to respective stories. It is found from the hinge pattern and capacity curves that in retrofitted buildings, capacity increased up to a certain storey and after that no increment in capacity was observed. It is concluded from the study that retrofitting of open ground storey building does not mean retrofitting of only ground storey but all such columns/stories where damage is getting distributed after the retrofit of open ground storey.
... Brick masonry infill wall is modelled as a single strut. Various expressions for strut width calculation have been proposed by Holmes [6], Mainstone [7], Decanini and Fantin [8], Paulay and Priestley [9], Liaw and Kwan [10], Durrani and Luo [11], Chrysostomou and Asteris [12]. Following Mainstone (1971) expression which has been adopted in IS 1893 (Part 1) : 2016 for strut width calculation. ...
Open ground storey buildings are quite popular in India due to availability of parking space and high commercial value of the land. However, these open ground storey buildings become first victims during earthquake ground shaking. The same is evident from the collapse and huge damage in ground story columns during past earthquake events. This led to a huge loss of life and property. Hence, there is an urgent need to take up retrofit activities of open ground storey buildings. There were some instances where retrofit activities were taken up on open ground story buildings. However, the performance of the building was not tested after ground storey retrofit. To build confidence among the general public, there is a need to demonstrate that the retrofitted buildings not only save lives but also resist earthquake with minimum damage. This paper is an attempt to demonstrate the same. In this paper, a case study of G+5 open ground storey building has been taken and nonlinear static pushover analysis (POA) is performed to obtain capacity curve. Later, the building is retrofitted in its ground/first storey and again capacity curve is obtained using the POA. It is found that the performance of the building significantly improved. However, from the hinge formation pattern, it is observed that the damage has propagated to the second storey. To improve the performance further, the second storey is also retrofitted and POA is performed again. Further, as per the damage propagation to upper stories, retrofitting is done to respective stories. It is found from the hinge pattern and capacity curves that in retrofitted buildings, capacity increased up to a certain storey and after that no increment in capacity was observed. It is concluded from the study that retrofitting of open ground storey building does not mean retrofitting of only ground storey but all such columns/stories where damage is getting distributed after the retrofit of open ground storey.
... Infills have been generally modelled by means of quite complex FEM micro-modelling approaches or simpler single-or multi-struts (reacting only in compression) approaches. Nevertheless, even recently, there is lack of unanimity about the best modelling approach among the various literature proposals (e.g., [4]- [6]), above all about the column-infill shear interaction modelling strategy, since, obviously, the shear demand in the surrounding RC members strictly depends on the modelling strategy to reproduce the infill response. More specifically, about the shear failure modelling in non-ductile RC frames, some standards propose simplified procedures aimed at considering the effects of the interaction between infill panels and surrounding RC elements. ...
RC buildings designed for gravity loads only or according to obsolete seismic codes are widespread worldwide also in seismic prone areas. Numerical and experimental studies highlighted that the presence of masonry infills in Reinforced Concrete (RC) frames leads to the increase in their lateral strength and stiffness. Nevertheless, post-earthquake observed damage showed that infills can also cause potential brittle failures due to the local interaction with structural elements, thus producing a limitation of deformation capacity of the surrounding frame, especially in sub-standard frames. A reliable modelling approach for the assessment of the as-built condition and the design of retrofitting solutions about this kind of failure is still needed.
Experimental tests on RC frames designed according to obsolete technical codes and infilled with clay bricks have been performed and presented in this work. The frames have been cyclically loaded with a quasi-static displacement pattern to simulate the seismic action. The experimental occurrence of significant shear damages is discussed, and the main outcomes are described, commented and compared to each other. The work lastly provides further data and modelling remarks towards a reliable numerical simulation of local shear interaction phenomena between infills and RC frames.
... The more accurate strut model is the one developed by Crisafulli and Carr (2007) and includes a formulation of two struts in each direction and a horizontal shear spring -which can require modeling time. This method makes some suppositions as to the position of the struts, the width of the struts, or the partition of masonry stiffness; issues that other researches have studied (El-Dakhakhni et al., 2003;Chrysostomou and Asteris, 2012). However, although they all work fine for a specific case, when other cases use the same parameters the results may not be as good unless very detailed analyses of the masonry parameters are carried out, as Mohyeddin et al. (2017) showed in their studies. ...
The presence of infill walls modifies the global structural response of frame buildings subjected to seismic loads. In evaluation studies, the stiffness of the structural elements and the mass of the building do not have great scattering; consequently, the variable to be analysed is the stiffness of the masonry. This investigation presents a process to determine a more realistic calibration of an existing building model using structural software and genetic algorithm programs made in Python 3 where the properties of the masonry were iterated to obtain modal periods similar to those obtained from ambient vibration tests. This programming can be freely downloaded and can be used in any optimisation case. The results highlighted the influence that non-structural masonry has over the overall behaviour of a building. It is also demonstrated that the use of a simplified macro model, with one spring that depicts the nonlinear performance of masonry, is an excellent option to address the limitations of commonly used software, as well as reducing processing time.
... Therefore, proposing a strut model for IF having various opening position and geometrical characteristics, that is capable of capturing force-displacement behaviour of such frames, is needed. Detailed and in-depth state-of-the-art reports can be found in the research works of Tassios [33], Crisafulli et al., 2000 [34], Chrysostomou and Asteris [35], Mohammadi and Nikfar [36], Di Trapani et al. [37], Yekrangnia and Mohammadi [38], Asteris et al. [39][40][41], and Liberatore et al. [42]. ...
This study aims to propose a multi-strut macro-model, capable of simulating the overall force-displacement behaviour of infilled frames with various opening configurations. For this purpose, the results of finite element modelling calibrated against several experimental data are employed to determine the characteristics of a multiple-strut model for such infilled frames. The results indicate that the size of the opening along with its position, compared to the size of the infill wall, can significantly affect both the inclination and also the effective width of the struts and therefore, the overall behaviour of infilled frames with opening. The proposed model is evaluated parametrically against FEM numerical results, with varying characteristics such as opening size and position, opening height-to-length ratio, height-to-length ratio of the infilled frame and relative rigidity of frame to the infill wall. The comparison of the derived results with the analytical and experimental findings demonstrates the ability of the model to approximate the lateral response of infilled frames with openings in a reliable and robust manner. A simple reduction factor for the ultimate strength of the perforated infilled frames is proposed based on opening size relative to infill wall size as well as relative stiffness of the frame and infill wall.
... According to experimental results, different analytical formulations are available in the literature to define the strength of the panel for each failure mode considered [72][73][74]; nevertheless, general formulations (i.e., avoiding the specific identification of the failure mechanism) are often preferred for predictive studies, in which the failure mode of the panel is unknown or not easily predictable (e.g., very similar values of the limit forces are predicted for different failure mechanisms and the determination of the failure mode is highly uncertain). ...
... The influence of infilled frames on the seismic behavior of RC frames has been investigated (Uva et al., 2012), pointing out some problems about the precision to the material parameters and the selection of the modelling. Chrysostomou and Asteris (2012) outlined the in-plane behavior and failure modes of infilled frames and provided simplified methods to predict these modes. The influence on the fundamental period of infilled frame with wall contribution to lateral rigidity of RC structures were evaluated (Ricci et al., 2011) and the contribution of frames with infill wall has been realized on the structural responses of frames by many researchers (Reinhorn, 1997;Nollet & Smith, 1998;Shota & Riddington, 2001;Pujol & Fick, 2010;Sattar & Liel, 2010;Hermanns et al., 2014;Korkmaz et al., 2015;Bas et al., 2017;Kaçım, 2017;Dilmaç et al., 2018). ...
... Here the empirical equation for the calculation of the equivalent strut width (w) by Mainstone [48,54] is taken, as it is not only widely used in the literature [e.g.: [55][56][57], but also suggested in the FEMA 306 [58] guidelines. For the maximum strength of the infill w can be expressed by Equation (1): ...
Significant damage to existing reinforced concrete (RC) frame structures during recent earthquakes has highlighted the potential detrimental effect of non-structural masonry infills. Several experimental studies have hence investigated the use of composite materials for in-plane retrofitting to reduce the risk of brittle collapse of the infills. In this review, the state-of-the-art on strengthening infilled RC frames with textile-reinforced mortars (TRM), a new class of composite material consisting of open-mesh textiles embedded in a cementitious matrix, is presented, highlighting the great potential of this retrofit solution for large-scale interventions on the existing building stock. A database of experimental results is compiled to evaluate the effect of different parameters on the effectiveness of the retrofitting applications. The stiffness of the fibre material, as well as the angle of application are found to be crucial factors. To ensure adequate analytical modelling for predicting the retrofitted behaviour, a macro-model, using an additional tensile tie to account for the TRM, is first calibrated by means of the experimental data gathered from the literature. Correlation between experimental parameters and the obtained effective strain is then assessed and an empirical formulation of effective strain in terms of fibre stiffness and retrofit amount is finally proposed.
The structural behavior prediction of the multistory reinforced concrete (RC) buildings with masonry infill walls (MIWs) during earthquakes is challenging. This paper presents a nonlinear macromodeling strategy seeking a simple, reliable, and low-cost computational analysis of the multistory RC buildings that comprise MIWs, and that use frames or shear walls (SWs) for resisting the lateral load. The strategy employed four plastic hinge (PH) models for tracking the deformations (flexural, shear, and torsion) of the frame elements and joints, a multilinear plastic link for modeling the MIW, and a nonlinear multilayer shell element for modeling the SW. A flexural PH model characterized by discretization into fibers, a recommended position, and an iterative estimating for the PH length using a distinct formula for each loading level was proposed. This strategy was validated through eleven macromodels investigating four bare frames, four MIWs frames, and a SW where the average ultimate lateral load error was 9.2%, 3.6%, and 0.4%, respectively. Finally, the structural behavior of real ten-story buildings with/without MIWs was investigated. The results showed that the MIWs increased the shear capacity and the lateral stiffness with an average of 44.3% and 118.6%, respectively. Also, both the frames buildings with MIWs and the bare SWs buildings showed approximately equal lateral load capacities. Local damages in the RC vertical elements and yielding of the MIWs were recorded simultaneously. However, the MIWs yielding (and also failure) occurred earlier for the frames buildings compared with the SWs buildings in which the stress was relaxed in their MIWs.
The present paper employed the Applied Element Method (AEM) to investigate the damage patterns in high-strength concrete (HSC) frames under extreme loads. Unlike existing computational techniques, AEM offers a distinct advantage in accurately identifying structural damage in all stages of loading conditions. The research focuses on analysing the impact of displacement-controlled in-plane cyclic loads on single- and multi-storey reinforced concrete frames with and without infill walls. AEM analysis coincided with experimental results, theoretical predictions, and FEMA 356 code provisions, affirming a reliable examination of cyclic damage patterns. The study reveals distinct damage patterns, shedding light on infilled frames' superior in-plane lateral load resistance compared to bare frames. Interestingly, multi-storey frames with soft-storey configurations exhibited higher resistance to lateral loads than those with infilled walls due to premature collapse of HSC columns. The study highlights the crucial role of robust, strong infill walls in reinforcing slender HSC frames. The results provide valuable insights for designing resilient structures under extreme operating conditions, thus contributing to advancing structural engineering practices.
In recent years, several seismic retrofitting projects of existing buildings have been involving additional measures to improve their energy efficiency, thanks to new regulations aiming at optimizing the buildings overall performance. Significant improvement is usually obtained through radical measures aiming at strengthening the infill panels, typically vulnerable to both out-of-plane overturning and in-plane cracking, and at enhancing their thermal insulation. Measures not disrupting the internal activities are generally favored. Back in 2012, two of the authors proposed a seismic-resistant double-layered infill panel for new buildings endowed with innovative flexible dissipative joints, placed along the horizontal brick interfaces, made from recycled plastic. In this work, those joints are upgraded to be used for retrofitting infill panels made of double-layered bricks and intermediate hollow space, as typical in most existing buildings. Within an existing infill panel, such joints create a system of parallel sliding surfaces along the horizontal bed-joints, after cutting off the mortar layer, thus channeling the in-plane deformation in the joints. On passing, it is noticed that the out-of-plane resistance is ensured by cantilevering elements protruding outwards from the joints surface, which prevent the panel from developing out-of-plane mechanisms. Such system has been preliminarily tested on a real-scale double-layer infill equipped with two joint lines under horizontal force. The experimental results have been compared with analytical models available in the literature for assessing stiffness and strength of the possible failure mechanisms, and a modified equation has been proposed for the mechanism involving bed-joint sliding induced by plastic joints.
The seismic retrofitting of existing masonry‐infilled reinforced‐concrete (RC) frame buildings is one major challenge of earthquake risk mitigation. In this paper, the use of promising novel alternative composite material, namely textile reinforced mortar (TRM) for seismic retrofitting masonry‐infilled RC frames with central openings is examined numerically, to the best knowledge of the authors, for the first time ever. This is achieved by performing a parametric study on a validated 2D numerical model of a three‐story masonry‐infilled RC frame with and without TRM considering different size of central openings. This parametric study aims to examine (i) the influence of central openings on the lateral response of masonry‐infilled RC frames subjected to cyclic loading and (ii) the lateral response of the three‐story masonry‐infilled RC frame with central openings retrofitted with TRM under cyclic loading. From the results obtained in this study, it was concluded that TRM contributes to increase the lateral capacity, stiffness, and the dissipated energy of infilled frames with openings and at the same time provides a more ductile behavior by delaying the strength and the stiffness degradation of infilled frames due to openings and further by delaying or even preventing brittle failures that occur on infilled frames due to the presence of the opening. New stiffness reduction factors for infilled frames with openings, and for TRM‐retrofitted infilled frames with openings are also proposed, which can be used with an equivalent compression strut model and with a tension tie‐model as an everyday practice tool for simulating infilled frames with central openings along the diagonal of the infill wall with and without TRM. A numerical sensitivity analysis is also performed aiming to investigate the influence of (i) the TRM reinforcement ratio and (ii) the type of mortar used for binding the textile reinforcement on the lateral response of the three‐story masonry‐infilled RC frame retrofitted with TRM subjected to cyclic loading. This study showed that by increasing the reinforcement ratio, or by using high‐strength mortars for binding the textile reinforcement, the lateral capacity of infilled frames is increased leading to a more ductile behavior, but this increase is not proportional to the increase of the reinforcement ratio or to the increase of the mechanical properties of the mortar.
Reinforced concrete (RC) structures with masonry infill walls constitute a significant portion of buildings, since their use is common in many countries due to the good performances of infills with respect to, temperature, noise, moisture, fire and durability. Therefore, RC structures with masonry infill walls are a popular form of construction in seismic regions too. Although, infill walls are mostly considered as non-structural elements and thus are typically neglected in the design process, the observations after earthquakes have shown that they interact with the structural system during seismic actions and that the traditional infill walls, connected with the mortar to the surrounding frame, are vulnerable to earthquake motions. Besides economic loss due to the repair or reconstruction of some infills, repair of damages to structural system, equipment, rental and relocation costs and general income losses, sometimes the consequences were total collapses of buildings and loss of human lives. Therefore, a huge effort has been made to consider the interaction of the structural system with the infill walls, but due to the complexity of the infill wall behaviour, no practical design procedures or solutions have been developed.
This thesis presents the INODIS system (Innovative Decoupled Infill System) that makes seismic resistant masonry infills in RC frames structures. This system decouples infill wall from the surrounding frame through a circumferential arrangement of the U-shaped elastomer placed between the infill panel and the frame columns and beams. This allows for relative displacements between the frame and infill, without damaging an infill and simultaneously enabling a support for the out-of-plane loads.
The behaviour of the decoupling system is investigated through the tests on system components and on RC frames filled with hollow clay bricks subjected to separate and combined in-plane and out-of-plane loads. These test results are compared to the results obtained from tests on RC frames with and without traditional infills. The experimental results showed quite brittle behaviour of traditional infills as well as significant reduction of resistances for sequentially applied loading and even higher reductions of the seismic resistance if the loads are applied simultaneously. This was all solved with the application of the INODIS system, which helped in reaching high in-plane drifts without experiencing damage in infill wall and at the same time providеd reliable connection for the out-of-plane loading. Additionally, viscoelastic behaviour of elastomers provided high level of energy dissipation and improvеd damping capacity of the infilled frame.
The experimental data has been used to validate the numerical micro-model. The developed numerical model describes the inelastic behaviour of the system, as indicated by the obtained results of the overall structural response as well as the formation of damage in the infilled wall. Satisfactory agreement was found between experimental and numerical results. The validated models have been used in parametric studies to identify the significant parameters influencing the behaviour of infilled frames with the INODIS system. The parametric study and experimental findings have been used to develop the design concept for the practical application of the INODIS system. Economic analysis of the solution showed the negligible increase of initial costs, thus it can be concluded that the INODIS system presents practically applicable solution.
In the last years, many research efforts have been focusing on the development of fragility and risk models of different building classes and structural typologies for large-scale seismic risk applications. Although the role of masonry infills is well recognised, less attention has been paid to the quantification of the variability surrounding their mechanical properties and how this might affect the collapse fragility curves and loss estimates. This study investigates and quantifies, in a thorough manner, the impact of the variability in the characteristics of masonry infill on the expected annual losses (EALs) of existing infilled reinforced concrete frames of different configurations. To do so, a fully integrated portfolio, representative of buildings designed according to the Italian codes in force between 1970 and 1980, is used as case-study. Infill-related variability is accounted for by means of a macro-level distinction of five common infill types, defined in terms of stiffness and shear strength. Moreover, building-to-building variability is also included through different geometrical configurations. Multiple-stripe analyses are carried out and fragility curves are developed for buildings with different heights, in-plan layouts and structural typologies. Finally, EALs are computed and analysed in a statistical fashion in order to quantify, in a simplified manner, the uncertainty induced by the variability of the masonry infill properties, as a function of the number of storeys and masonry infill typology.
Evaluating the structural performance of low-rise RC buildings with infill walls is an essential issue in Thailand, as most infill walls were not designed for lateral load resistance. The purpose of this study was to predict the structural behavior and illustrate the effects of infill walls. Residential, commercial, and educational buildings were selected as representative buildings with different patterns of infill walls. Based on the results, infill walls contributed to considerable strength and stiffness. Most of the infill walls that affected the low-rise buildings were at the ground floor level. The behavior of the buildings that had a contribution of infill walls was found to be brittle until the infill walls collapsed, and then the buildings became ductile. Some patterns in which infill walls were placed improperly led to a torsional effect, resulting in columns in the affected areas reaching failure criteria more than those without this effect. Considering the NLRHA procedure, only infill walls on the ground floor contributed to the building being subjected to a ground motion. The fully infilled frame tended to reach the infill crack before the other patterns. For the UMRHA procedure, only the first vibration mode was adequate to predict seismic responses, such as roof displacement and top-story drift.
Infilled frames are usually modelled in the context of global building analysis using simplified procedures without considering the aspects resulting from the interaction between the panel and the frame. Other aspects, such as adequate design of the floor beams and the beam-columns’ joints, and control of potential sliding shear failure of the columns, that significantly affect the structural response, are also typically not accounted for. In the present work it is intended to look over the literature to evaluate the state of the art regarding the lessons learn from recent earthquakes, the evolution of the structural codes considering the infill masonry panels, and how this influences the evolution of the numerical models and the experimental works to overcome the existent gaps.
In regions of high seismicity, infilled frames are commonly used for low and medium-height buildings. "Infilled frame" is a composite structure. It is formed by one or more infill panels surrounded by a frame. Infilled frame also refers to the situation in which the frame is built first and then infilled with one or more masonry panels. The primary function of masonry was either to protect the inside of the structure from the environment or to divide inside spaces. The presence of masonry infills helps the overall behavior of structures when applying lateral forces. The lateral stiffness and the lateral load capacity of the structure largely increase when masonry infills are considered to interact with their surrounding frames. In this paper, ANSYS 14 software is used for analyzing the infill frames. Echo state neural network (ESNN) has been used to supplement the estimation of stress values of the proposed infill frame model. The number of nodes or reservoirs in the hidden layer for ESNN algorithm varies depends upon the accuracy of estimation required. Exact number of reservoirs is fixed based on the trial and error method, through which the accuracy of estimation by the ESNN is achieved.
The treatment of masonry infill walls as non-structural elements in the design of reinforced concrete buildings has been refuted by the losses and damage recorded when these buildings were exposed to seismic loads. Between these walls, there is a type widely used in reinforced concrete buildings in Algeria. This article aims mainly to highlight the role of the infill masonry walls in improving the seismic response of reinforced concrete buildings to resist seismic loads. To demonstrate the above role, we have analyzed several models of two-dimensional frames of a multi-storey building located in a high seismic site, according to the classification of the current Algerian seismic code, with double-leaf hollow brick masonry, which is the most used infill material in Algeria. This analysis is based on the response spectrum method using the finite element software ETABS, taking into account the most important requirements of the current Algerian seismic code. We used the parameters of period, base shear, maximum displacement, and stiffness to evaluate the ability of these frames to respond to seismic loading; we analyzed several models in terms of the number of storeys. After analyzing all the models, we compared the results obtained, and then we were able to define this role and see what contribution these walls can make to the analytical aspect. Finally, we were able to know the positive role that these walls can play in improving the seismic performance of this type of building.
A large part of the existing building stock was not designed according to the current codes in seismic prone regions. The poor performance of some reinforced concrete structures was related to the presence of the masonry infill walls. Although the infill walls can increase the lateral resistance of frames in many cases, it is widely recognized that there is a high vulnerability of the masonry infill walls subjected to loadings along and perpendicular to their plane. Several collapses were observed after past earthquakes in infilled frame buildings. For this reason, different retrofitting design approaches have been proposed and used during the last years; however, many of them do not fit with the building’s owners’ economic demands or technical knowledge of the workmanship. Over the years, significant research has been conducted for masonry wall elements retrofitted with textile-reinforced mortar (TRM). However, much less has been carried for masonry-infilled frame RC frames. Thus, this manuscript aims to provide a literature review about research on assessing the effectiveness of using TRM technique to reduce masonry-infilled RC frames’ seismic vulnerability. Experimental findings will be deeply analysed to provide full insight concerning the TRM’s efficiency under in-plane and/or out-of-plane demands of infilled frames and some variables such as anchorage of the TRM to the structure. Numerical modelling approaches to simulate the complex behaviour of infilled frames with TRM are also presented to stress their benefits or limits. Covering completely all aspects of this manuscript is essential to briefly describe the studies conducted so far to examine either numerically or experimentally the effectiveness of using TRM for retrofitting masonry wall elements.
An in-plane finite element model of infilled frame systems is formulated. A frame–infill interface capable of transferring only normal compressive contact forces is defined. The complex phenomenology affecting these systems is explored, with a focus on the contact/separation conditions at the interface. Comparisons with previously reported experimental and numerical findings are made, and the model is validated. Parametric analyses are performed. Interpolation formulae are determined, which estimate frame–infill contact lengths and global stiffness in the elastic regime.
Calculus complexity, time-consuming and high computational effort of the nonlinear dynamic analysis coupled with the complexity of simulating the interaction between masonry infill walls and reinforced concrete frames cause this fact that infill panels are usually considered as the non-structural elements to analyze and design the process of reinforced concrete frames infilled with masonry walls. In this study, to predict the influence of masonry infill panels on the imposed damage of moment-resisting reinforced concrete frames (MRRCFs) under earthquake excitation, incremental inelastic dynamic damage analyses are performed several MRRCFs under twenty seismic ground motions. The MRRCFs are simulated once without considering masonry infill wall effect (as bare frames) and another one considering masonry infill wall effect (as infilled frames). The diagonal compression strut model used to simulate the infill walls is compared with some other proposals in terms of the equivalent strut width, the bed-joint sliding shear strength, the diagonal tension cracking strength, the corner crushing strength, and the diagonal compression strength. Results show that the equivalent strut width, the diagonal tension cracking strength, and the corner crushing strength predicted by FEMA306 are in reasonable compliance with the model used in this study. The capacity and damage curves of bare, and partial, and full infilled frames using incremental dynamic analyses are achieved and compared. The consequences proved that masonry infill walls improve the lateral load-bearing capacity of MRRCFs and decrease the imposed damage of these frames in the seismic excitations. Furthermore, two relations are derived to predict the damage of bare and infilled frames under the earthquake excitations. To assess the accuracy of proposed relations, three new frames are designed. The values of their seismic damage are achieved through inelastic damage analyses and presented relations. Comparing the outcomes confirms the validity of proposed relations.
In the world, many existing buildings with RC framed structure are extremely vulnerable, as they were designed to sustain gravity loads only, or to resist seismic actions lower than those expected today. Since a complete renewal of the existing building heritage is not possible, the seismic assessment of existing structures has gained importance in recent years to identify the structural deficiencies and design the most appropriate retrofit interventions. This paper proposes a multimodal adaptive nonlinear static method of analysis named overDamped Displacement Adaptive Procedure (D-DAP). This method has been developed from the combination of the approaches adopted by Pinho et al. and Lenza et al. In addition, the D-DAP explicitly considers the increase of the energy dissipation due the cumulated damage in the structure by updating the value of equivalent viscous damping ratio according to a new damping law properly calibrated for RC frames with and without infill panels.
The threat to human lives and the economic losses due to high seismic vulnerability of non-engineered traditional masonry infills subjected to earthquakes have been highlighted by several post-seismic surveys and experimental and numerical investigations. In the past decades, researchers have proposed different techniques to mitigate problems related to the seismic vulnerability of traditional masonry infills; however, a viable, practical, and universally accepted solution has not been achieved yet. Among the possible innovative techniques, the one using ductile (or pliable) infills have shown promising results in recent experimental tests. These infills have provided, indeed, a reduced in-plane stiffness and a very high displacement capacity. The research units of the University of Pavia/EUCENTRE (Italy) and the University of Newcastle (Australia) have proposed two different systems for ductile masonry infill based on dividing the masonry panel into a number of segments interconnected through horizontal sliding joints. The ductile masonry infill proposed by the University of Pavia subdivides the masonry panel into four horizontal subpanels using specially engineered sliding joints and presents a deformable mortar at the infill/structure interface, while the one conceived by the University of Newcastle is made of mortar-less specially shaped masonry units capable of sliding on all bed joints. The experiments conducted on the two novel systems have permitted the calibration of two numerical macromodels capable to replicate the overall in-plane seismic response of these ductile masonry infills. One approach is based on a spring model, as usually adopted for traditional masonry infill; the other calibrates the response of a semi-active damper model. The calibrated macromodel approaches have been adopted to demonstrate the enhanced behavior and the reduction of the seismic vulnerability of reinforced concrete (RC) framed structures with the employment of the ductile infills in comparison to structures with non-engineered masonry infills.
Content of this proceedings discusses emerging trends in structural reliability, safety and disaster management, covering topics like total quality management, risk maintenance and design for reliability. Some papers also address chemical process reliability, reliability analysis and engineering applications in chemical process equipment systems and includes a chapter on reliability evaluation models of chemical systems. Accepted papers from 2019 International Conference on Reliability, Risk Maintenance and Engineering Management (ICRRM 2019) are part of this conference proceeding. It offers useful insights to road safety engineers, disaster management professionals involved in product design and probabilistic methods in manufacturing systems.
The analytical modelling of infilled frames is a complex issue because these structures exhibit a highly nonlinear inelastic behaviour resulting from the interaction of the masonry infill panel and the surrounding frame. This paper presents a general review of the different procedures used for the analysis of infilled frames, which can be grouped in local or micro-models and simplified or macro-models, depending on the degree of refinement used to represent the structure. The finite element formulation and the equivalent truss mechanism are the typical examples of each group. The advantages and disadvantages of each procedure are pointed out, and practical recommendations for the implementation of the different models are indicated.
In this paper, a realistic criterion is proposed to describe the frame-infill separation, in order to better simulate the complicated behavior of infilled frames under lateral loads. The basic characteristic of this analysis is that the infill/frame contact lengths and the contact stresses are estimated as an integral part of the solution, and are not assumed in an ad-hoc way. In order to implement the method, a specific computer program for the analysis of infilled plane frames, under lateral loads, has been developed. Using this method, the response of a single-bay single-story masonry infilled R.C frame, under a lateral load in the beam level, has been investigated. The large magnitude of the variation of the contact lengths between the infill and the different frame members is clearly shown.
Masonry infill panels in framed structures have been long known to affect strength, stiffness, and ductility of the composite structure. In seismic areas, ignoring the composite action is not always on the safe side, since the interaction between the panel and the frame under lateral loads dramatically changes the stiffness and the dynamic characteristics of the composite structure, and hence, its response to seismic loads. This study presents a simple method of estimating the stiffness and the lateral load capacity of concrete masonry-infilled steel frames (CMISFs) failing in corner crushing mode, as well as the internal forces in the steel frame members. In this method, each masonry panel is replaced by three struts with force-deformation characteristics based on the orthotropic behavior of the masonry infill. A simplified steel frame model is also presented based on the documented modes of failure of the CMISF. The method can be easily computerized and included in nonlinear analysis and design of three-dimensional CMISF structures.
A two-dimensional computational model for infill walls is presented. The behavior of an infill wall is prescribed by a strength envelope and a hysteretic loop equation which provide smooth continuous curves. The infill is idealized with six compression-only inclined struts, which follow the behavior defined by the strength envelope and hysteretic loop equations. Three parallel struts are used in each direction, and the off-diagonal struts are located to represent the interaction between the infill and confining steel frame at locations along the beam-column spans where plastic hinges have been observed to form. The advantages of this analytical model are the following: (a) both strength and stiffness degradation of infill walls are modeled; (b) the parameters of the model have physical meaning and can be readily adapted to fit experimental data; (c) the off-diagonal struts allow modeling of the interaction between the infill and the bounding frame; and (d) local behavior, such as the effects of openings, lack of fit, and interface conditions, can be modeled.
The evaluation of the seismic performance of masonry-infilled reinforced concrete (RC) frames has been a major challenge for structural engineers. This paper addresses pertinent issues on the development and calibration of nonlinear finite-element models for assessing the seismic performance of these structures. The modeling scheme considered here combines the smeared and discrete crack approaches to capture the different failure modes of infilled frames, including the mixed-mode fracture of mortar joints and the shear failure of RC members. A systematic approach is presented here to calibrate the material parameters, and the accuracy of the nonlinear finite-element models has been evaluated with experimental data. The comparison of the numerical and experimental results indicates that the models can successfully capture the highly nonlinear behavior of the physical specimens and accurately predict their strength and failure mechanisms. The validated models have been used to assess the sensitivity of the numerical results to the modeling parameters and to identify the critical material parameters through a parametric study.
This paper presents research on the behavior of a type of building popular in high seismic zones with a lateral-load-resisting system consisting of masonry-infilled reinforced concrete (RC) frames. Older buildings of this type typically were designed for gravity loads in combination with insufficient or no lateral loads, therefore they do not meet current seismic code requirements. Also, the participation of infill panels in the lateral load resistance of RC frames was not recognized in the original design, often resulting in an overly conservative design. In an attempt to determine the seismic vulnerability of this type of structure, an experimental program was carried out to evaluate the behavior of five half-scale, single-story laboratory models with different numbers of bays. The results indicated that infilled RC frames exhibit significantly higher ultimate strength, residual strength, and initial stiffness than bare frames without compromising any ductility in the load-deflection response. Furthermore, the number of bays appears to be influential with respect to the peak and residual capacity, the failure mode, and the shear stress distribution.
Five one-half scale reinforced concrete frames were constructed and tested under static reversed cycle loads to determine experimentally the effectiveness of infilled walls in strengthening and stiffening existing framed structures against earthquake loads. An unstrengthened portal frame and a frame with a monolithically cast infilled wall provided references for the three strengthening techniques. The first wall was cast-in-place within the existing frame; the second was a single precast panel that was bolted to top and bottom beams; and the third was made of six individual precast panels that were connected to the top and bottom beam and to each other. Tests showed that the cast-in-place wall strengthened the frame so that its capacity was similar to the monolithically cast specimen but that the cast-in-place system dissipated only one-half the energy. The multiple precast panel wall demonstrated greater ductility than the other infilled structures; although its maximum load capacity was about one-half that of the monolithically cast specimen.
An analytical model and a computer program were developed for nonlinear dynamic analyses of plane frames with filler panels having gaps at the sides and tops of the panels. Beams and columns of the frame were represented by plane-frame elements. Filler panels were modeled by rectangular finite elements having various nodal displacement patterns. Criteria were devised for monitoring the opening and closing of gaps, and a procedure is described for modification of the stiffness matrix upon closing and opening of the gaps.
This paper reviews the current state of knowledge of infilled frames and its applicability to practical designs. Factors affecting the formulation of a consistent code of practice for infilled frames are discussed. The applicability of the available information on the stiffness and strength of infilled frames to the design of reinforced concrete frames infilled with masonry is critically studied.
The paper presents a review of the literature and the salient features of investigations carried out on the behavior of infilled frames under static loads. The limitations and the general applicability of the results have been critically discussed. The study described was carried out on two types of infilled frames: steel frames infilled with mortar, concrete, brickwork; and reinforced concrete frames infilled with brickwork.
The behaviour of in-filled frames is influenced by the presence of openings such as doors, windows and ventilators in the claddings or walls. The openings reduce the stiffness affecting strength and failure pattern. Their size and location have a bearing on the interaction between frame and infill panel altering the behaviour. Parameters such as structural displacement, compressive and tensile stress trajectories in the panel and support reactions and forces in frame members were investigated for a single storey infilled frame. The frame was analysed for a centrally located window and a door located at the centre and at two end positions near the columns. The analysis followed finite element method and used incremental load. It accounted for the non-linearity at the interface and the elastic properties of the frame and the infill. It shows that the stiffness of the infilled frame decreased by 20-80% due to openings.
A computer program using the finite element method for the non-linear analysis of shear wall panels in frames is described. The modified Newton-Raphson method with load incrementation is used. A technique to overcome the numerical instabilities that have been encountered previously when using the method is described. Accelerators to improve the rate of convergence are also included in the program. Analyses of full-scale shear wall panels in reinforced concrete frames using the computer program are described. In all cases, reasonably good agreement has been obtained between the results obtained from the computer program and those from the laboratory and field tests. Subsequently, an extensive parametric study has been carried out using the computer program to provide data for a design method for infilled panels proposed by the Authors.
Single-story multibay infilled frames without shear connectors are studied in conjunction with single-bay infilled frames. A nonlinear finite element method is employed for the analysis, taking into account nonlinearity of materials, cracking in the panel, and separation/friction/slip at the interface between panel and frame. The study covers the entire loading range from the initial elastic stage until the ultimate failure stage. Models were tested to verify the theoretical results in terms of the load-deflection behavior, the ultimate load, and the interaction stresses at the panel/frame interface. The comparison of theoretical and experimental results is generally good.
The paper concerns the use of masonry infills for bracing steel or reinforced concrete frames against horizontal forces. Results are presented of a series of elastic finite element stress analyses of infilled frames. By providing for the possibility of separation between the frame and infill and for the possiblity of loss of friction along the remaining lengths of contact, the adopted theoretical model contains important aspects of behavior not included in previous studies. The influence of a range of parameters has been investigated, including separating or non-separating and frictional or nonfrictional boundaries, varying length to height of infill ratios, varying frame stiffness, varying rigidity of beam to column connections, and multi-story and multi-bay structures.
The experimental phase consists of quasistatic cyclic load tests on one-third scale model subassemblages of the lower three stories of an 11-story, three-bay frame with infills in the two outer bays: (1)Frame members (particularly the columns) are designed for high rotational ductility and resistance to degradation under reversed cyclic shear loads; (2)gradual panel degradation is achieved using closely spaced infill reinforcement; and (3)panel thickness is limited so that the infill cracking load is less than the available column shear resistance. The analytical phase consists of developing relatively simple, macroscopic mathematical models for predicting the experimentally observed bare and infilled frame behavior. The infilled frame model is found to give excellent predictions of observed response. It is concluded that the model developed and the procedure used can be applied to the analytical prediction of the response of large, engineered infilled frame structures to severe lateral forces.
Infilled frame structures may, for a variety of reasons, have initial gaps between the frame and the infill. The results from an investigation into the influence of these gaps on the behavior of this structural form are presented. The investigation consisted of a series of six full-scale tests on blockwork infilled steel frames together with finite element analyses of these structures. The results indicate that even the relatively small initial gaps used in the tests significantly affect the structural behavior of infilled frames and that these effects are largely undesirable. It is thus concluded that initial gaps should be avoided wherever possible. As a result, the use of masonry infilled reinforced concrete frames is questioned because of the desirability of providing an initial gap between the infill and the top beam of the frame to allow for creep in the columns of the frame.
This paper describes a new method of analysis and design for steel frames with concrete or masonry infilling walls subjected to in-plane forces. The method is based on data generated from previous experiments as well as results from a series of nonlinear finite-element (NLFE) analyses. The method accounts for elastic and plastic behavior of infilled frames considering the limited ductility of infill materials. The proposed method predicts the strength and stiffness of infilled frames as well as the infill diagonal cracking load. The method also allows for the major practical imperfections, such as lack of fit and shrinkage of the infill. Variations, such as infill aspect ratio and beams having different strength and stiffness from the columns, are accounted for and it is concluded that the behavior of frames with pin or semirigid joints can also be predicted. The method is further developed to model multistory infilled frames as braced frames, replacing the infills by equivalent diagonal struts.
Codes of practice for multi-story buildings allow extensive interaction at collapse between floors and frames (via yield line theory or the strip method) but the corresponding wall-frame interaction has been neglected by comparison, This facing up to the problem of immediate simplifications for design codes and special difficulties in deciding partial safety factors for real composite structures. Suggestions for research and design examples are included.
The nonlinear behaviour of non-integral infilled frames (in which the infill and the frame are not bonded together) is studied both experimentally and analytically. In the theoretical study, finite element method is used and the nonlinearities of the material and the structural interface are taken into account. It is shown that the stress redistributions towards collapse are significant, and that the strength of non-integral infilled frames is very much dependent on the bending strength of the frame. The effects of initial lack of fit and friction at the interface are also studied theoretically. Furthermore, an empirical formulae for estimating the equivalent strut width is proposed.
Introduction Masonry Walls Masonry Moment-Resisting Wall Frames Masonry-Infilled Frames Minor Masonry Buildings Design Example of a Slender Masonry Cantilever Wall Design Example of a Three-Story Masonry Wall with Openings Assessment of Unreinforced Masonry Structures
The influence of brick masonry infill properties on the behavior of infilled frames is studied, using a finite element model to simulate the behavior of infilled frames subjected to racking loads. The finite element program incorporates a material model for the infill brick masonry which includes appropriate elastic properties, inelastic stress-strain relations and a failure surface. The program is capable of simulating progressive cracking and final failure of the infill. The model is verified by comparison with racking tests on infilled frames. It is then used to carry out a more extensive study of the influence of infill properties on the failure loads and failure modes of the panels. It is shown that the behavior of the composite frame not only depends on the relative stiffness of the frame and the infill and the frame geometry, but is also critically influenced by the strength properties of the masonry.
Based on the findings of non-linear finite element analysis, a plastic theory of integral infilled frames is proposed, in which the stress redistribution toward collapse and the shear strength at the infill/frame interface are taken into account. The theory is applicable to both single story and multi-story integral infilled frames, and comparison with experimental results gives good agreement. Design recommendations for multi-storey integral infilled frames are given.
A procedure based on the finite element method for analyzing infilled framed structures is described. In particular, it is shown that interaction between infill panels and frames can be modelled with versatility and accuracy using modified friction elements. The range of practical values of the parameters controlling the behavior of these elements is determined experimentally, and it is shown that interactive behavior is not dependent on their precise values. When the procedure is used to determine the lateral stiffness of single frames, it is shown that fairly coarse finite element meshes can be used and the good agreement is obtained with published experimental results. The results of tests of model multi-storey, multi-frames are reported and theoretical predictions again shown to conform adequately. The limiations of the practice of replacing infill panels by equivalent diagonal struts, when analysing framed structures, are discussed.
To deal with infilled frames with or without opening in the infill, an approximate method of analysis based on the concept of equivalent frame is presented. Experimental results on the stiffnesses of two elastic models having various sizes of opening in the infill are compared with the analytical results. The comparison shows good agreement when the central opening is more than half of the full infill area.
Large-scale structural clay tile infilled steel frames were tested under in-plane loading. All infills failed through corner crushing, and the failure load was relatively insensitive to framing characteristics. An analytical procedure was proposed in which the peak strength of the infill for the corner crushing limit state is a function only of f(m)' and the thickness of the infill. This simple method predicted the strength better than any other analytical method. A piecewise linear equivalent strut was used to model the stiffness of the infill. The behavior of the structural clay tile infills (cracking, tile failure, and stiffness) was better correlated with actual displacements, than with nondimensional story drift (displacement divided by height). Bending moments and axial forces in the bounding frame were examined, with the infill having little effect on the moments in the columns. The results of several other configurations, including a repaired infill, an eccentric infill, an infill with column gaps, and an infill with a corner opening, were also reported.
Seismic evaluation of a two-story, two-bay reinforced concrete frame infilled with masonry was performed by pseudodynamic testing of a half-scale specimen. The second-story infill included window openings. The specimen was subjected to four tests of increasing magnitude based on the Taft ground motion. Explicit numerical integration with a small time step, soft-coupled load system, and an iterative actuator control algorithm limited the displacement errors normally associated with pseudodynamic testing of stiff structures. The final sequence of tests produced diagonal cracking in the upper story, but primarily bed joint shear cracking in the lower story. Relations between the type of observed cracking and story drift-story shear response are explored. Compressive strut mechanisms are defined from the experimental values of moments and axial forces in the frame and infill panel strains. Estimates of story stiffness from several simple strut models were found to bound the experimentally measured values for both the first- and second-story walls prior to significant damage. Friction-based analytical estimates of panel shear strength were found to underestimate the measured strength and to be sensitive to the assumed coefficient of friction. Available methods for estimating shear strength that neglect infill-frame interaction were found to largely underestimate measured shear strength.
An analytical macromodel based on an equivalent strut approach integrated with a smooth hysteretic model is proposed for representing masonry infill panels in nonlinear analysis of frame structures. The hysteresis model uses degrading control parameters for stiffness and strength degradation and slip ''pinching'' that can be implemented to replicate a wide range of hysteretic force-displacement behavior resulting from different design and geometry. The paper presents the development of the hysteretic model and the definitions of the control parameters, which can be determined using any suitable theoretical model for masonry infills. An available theoretical model for simplified engineering evaluation of masonry infilled frames was explored for estimating the control parameters of the proposed macromodel. The macromodel was incorporated in a nonlinear structural analysis program, IDARC2D Version 4.0, for quasi-static cyclic and dynamic analysis of masonry infilled frames. Simulations of experimental force-deformation behavior of prototype infill frame subassemblies are performed to validate the proposed model. A lightly reinforced concrete frame structure is analyzed for strong ground motions to evaluate the influence of masonry infill panels on the dynamic response.
This paper summarizes studies in which the effects of masonry and lightweight concrete infills on R/C moment existing frame buildings were studied experimentally and analytically. The experimental investigation consisted of a series of quasi-static cyclic and monotonic load tests on 1/3-scale models of the lower 3-1/2 stories of an 11 story-three bay reinforced concrete frame infilled in the outer two bays. Different panel material and reinforcement combinations were tested. For reasons of economy, ease of construction, favorable mechanical properties, and efficiency of different types of masonry infill, it was concluded that the most promising panel configuration consisted of solid brick laid in mortar reinforced with two mats of welded wire fabric, one bonded to each side of the wall in a layer of cement stucco (mortar). The implications of these experimentally obtained results are analyzed by investigating how the infills affect the dynamic response of R/C moment resisting frame buildings, as well as considering the effect of these implications on design of new buildings, and retrofitting of existing buildings located in regions with differing seismic risk.
An analytical method taking into account the axial deformations of the members of the frame and the slip at the interface has been summarised for linear elastic behaviour of a homogeneous and isotropic infill. The theoretical and experimental results have been compared.