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Evaluation of progressive collapse behavior in reinforced concrete buildings
Abstract
Progressive collapse is a catastrophic chain reaction of failure of a structure that is caused due to loss of vertical load bearing element of the structure, resulting damage of a part of the structure or entire structure. In our research work 10 storey regular Reinforced Concrete framed structure is considered and is seismically designed with IS 1893:2016 in SAP2000 version 20 modeling. The different column removal scenarios both in plan and elevation suggested by guidelines were examined by alternate load path method using nonlinear staged construction available in the software and then identify the potential of the structure to withstand progressive collapse. Numerical results were compared by analyzing columns and beams separately by calculating demand capacity ratios and the requirement of percentage of steel for failed structural elements are predicted both in flexure and shear stresses. Our objective is to provide clear conceptual step-by-step descriptions of various procedures for progressive collapse analysis 3D (three-dimensional) Finite Element Methods (FEM) and non-linear static push-down analysis in SAP2000 software was used to assess the progressive collapse potential of a typical gravity-load designed mid-rise reinforced concrete building with open ground floor. The beam is actually designed to resist the shear force up to 39.84 kN. So in order to resist the shear failure we need to provide enough vertical reinforcement. The failed structural elements were re-designed to resist progressive collapse in order to satisfy the acceptance criteria recommended by the guidelines. It’s showed that the incorporation of perimeter beams in buildings improved the progressive collapse resistance as it reduces joint displacement and chord rotation at column removal locations by providing sufficient stiffness and load paths for increased gravity loads. The study results can be used to develop and calibrate the nonlinear numerical model for analyzing high-rise building progressive collapse behavior and can help provide information that may improve new and existing reinforced concrete core-wall building robustness against progressive collapse.
... Many theories of progressive collapse of structures [14][15][16][17][18][19][20][21][22][23][24][25][26][27] is explained by the fact that it is impossible to construct a theory based on the Lagrange principle that consistently excludes structural elements from operation. The structural optimization theory is developed to reduce the amount of residual load-bearing capacity [28][29][30]. ...
... If nodal displacements are found out, stimulated by external actions, then Eqs. (17) lead to: ...
The paper discusses the theory of critical strain energy levels for structures with lumped parameters. The theoretical assumptions and profs for common case are presented. The idea of external actions and strain energy field separation leads to the minimum strain energy principle. It has the self-stress of the structure physical sense. In the general case, a structure's extremal values of parameters are determined from an eigenvalue problem. The critical levels criterion means the self-stress state change. The strain energy consists of two parts: strain energy, which equilibrates the action work, and residual strain energy, which does not allow a deformable body to collapse. This allows for the total and residual strain energy to be calculated. The traditional problem formulation does not give us that option. The proposed theory is illustrated on a rod system, which explains the change in the self-stress state of the structure in a simple manner. The static matrix and stiffness matrix are obtained for the three-bar structure. The eigenvalue problem allows us to obtain the principal values of the nodal reactions and displacements of the structure. New formulations of structural design and structural analysis tasks are given. The results are compared with classical methods of solution. The formulations of weak link problems and progressive limit state problems are given. A structure's residual load capacity is evaluated by the residual strain energy.
... Further experimental studies have been also accompanied by refined numerical interpretations [7,[11][12][13], investigating the role of geometrical and mechanical parameters on the progressive collapse response of reinforced concrete structures, as well as the role of the boundary conditions. Other studies focused on the numerical simulation of the progressive collapse response of 2D and 3D case-study frame structures subject to quasi-static and dynamic simulations [14][15][16][17]. In this context a focus on strengthening and retrofitting techniques to mitigate progressive collapse was also provided [18,19]. ...
... where h c and l b are the interaxis length of the column and of the beam, and d is the length of the diagonal strut obtained as d = ̅̅̅̅̅̅̅̅̅̅̅̅̅ ̅ h c + l b √ . Parameters c* and β* are evaluated by: c * = 0.249 − 0.0116 ν + 0.567 ν 2 ≅ 0.254 β * = 0.146 − 0.0073 ν + 0.126 ν 2 ≅ 0.147 (14) where ν is the Poisson's ratio of the infill along the diagonal direction, which can be set as 0.1. The parameter λ* is evaluated by means of the formula initially proposed by Papia et al. [36], where the positions of l b and h b are inverted to take in consideration the different load directions and using the conventional Young's modulus (Ẽ m ) so that: ...
The response of reinforced concrete (RC) frame building structures to exceptional events like explosions or impacts causing the loss of a primary structural element depends on the robustness of the structural confguration. In the case of a sudden column loss, the resisting mechanism of the involved spans substantially changes,
while a progressive collapse mechanism can develop under the arising dynamic loads. The presence of masonry infll walls can substantially modify the overall response to a sudden column loss scenario. In this context, this
paper investigates the response of reinforced concrete frame structures undergoing instantaneous column losses in order to assess the influence of masonry inflls on the progressive collapse response under dynamic load demands. A recently formulated equivalent-strut macro-modelling approach is employed to reproduce the mechanical interaction between infll walls and the frames. A ten-storey, six-bays 2D reinforced concrete frame is
selected as a case study structure considering different reinforcement layouts (seismic or non-seismic design) and
column loss scenarios (central column or corner column loss). The simulations are carried out using the fbersection beam/column elements available in the OpenSees software platform, as they can account for the arching mechanism developing in the post-cracked regime. The dynamic responses of the case-study tests to the
sudden column loss scenarios are assessed with and without the inclusion of masonry inflls within the structural models. Results demonstrate that masonry inflls introduce a substantial modifcation of the resisting mechanism and of the dynamic response, limiting the propagation of progressive collapse in most of the considered cases.
... Kiakojouri et al. (2022) investigated the impact of some parameters on strengthening structures against progressive collapse. Vinay et al. (2022) redesigned the failed members of the RC structure to meet the acceptance criteria of the guidelines to resist progressive collapse. Chen et al. (2023) studied the impact of seismicity and the number of stories on the progressive collapse resistance of RC structures. ...
The damping ratio of reinforced concrete structure cannot be considered as a constant value, and some parameters such as increasing the age of the structure, the corrosion of the reinforcements, and the ground motion amplitude can significantly change the damping ratio. This study investigates the effect of the damping ratio on dynamic increase factor (DIF) against sudden column removal of structures in terms of progressive collapse. To this end, various reinforced concrete structures with moment-resisting frames and regular rectangular plans with different stories and span lengths were designed based on ASCE7 and ACI318-14 in SAP2000. Several column removal scenarios were examined in various locations of the structures by the alternate load path method, and several nonlinear dynamic and static analyses were performed to achieve the data points. Four different curves were fitted to the extracted data points using SPSS, and four modified empirical equations were derived for DIF at damping ratios of 1%, 5%, 10%, and 15%. The difference between the curves shows the impact of the damping ratio on the DIF. In order to integrate four equations, an empirical equation was derived to estimate DIF, including the damping ratio. Moreover, the effect of some other parameters such as the beam span lengths and the location of column removal in the stories and plan on the DIF was investigated and discussed. The equation proposed by the guidelines for DIF provides underestimated and upper estimated values for the DIF in the structures with damping ratios, respectively, less than 5% and higher than 5% because this equation does not include the effect of the damping ratio. Therefore, the derived equation in this research can be suggested as an alternative to the equation proposed by the guidelines.
... Another theory that requires a similar methodology is the calculation for progressive collapse [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Regulatory documents of many countries require the analysis of the erected structure for the successive disabling of structural elements that have been subjected to accidental or beyond design effects. ...
This article examines the application of the theory of critical strain energy levels to the determination of the limiting states of rod systems. A redundant truss is chosen to illustrate the peculiarities of changes in the self-stressing states of the structure at critical strain energy levels. The removal of ties when they reach their stress or strain limits leads to a change in the state of self-stress in the structure, which is illustrated by the removal of the rods in the trusses. The matrix notation of the governing equations for the structure allows us to visualize both the formulation of the problem and the course of its solution. We present the formulation and algorithm for solving the problem of a weak link in the structure by the example of a five-core redundant truss. The basic equations of matrix structural mechanics are given, allowing us to implement the algorithm and to determine the unknown parameters of the problem in the form of the method of displacements and the method of forces. The mathematical model of the problem is presented in the form of an eigenvalues problem, which allows us to investigate the extreme properties of the structure’s strain energy in the whole area of admissible parameter values, including the boundaries. The eigenvalues and eigenvectors make it possible to determine the extreme values of the nodal reactive forces of the structure or displacements, depending on the chosen formulation of the problem. The internal forces and deformations in the rods depend on the nodal vectors of external influences. The applied design load is balanced by the internal forces of the system and remains unchanged. This follows from the equality of the work of external forces to a part of the potential energy of the structure. The remaining part of the strain energy allows us to find the limit values of the reactive response of the structure to external actions. Additional actions on the structure can lead to the bearing capacity lost if they exceed the limits of the structure’s response. Examples show an algorithm for finding the weak link in a structure and identifying the rods that will be the first to fail under external loads. The matrices of stiffness and flexibility are formed, and the eigenvalues and vectors are found, which allow for the construction of the limit surface of allowable influences on the structure.
... The crystallite size of particles found in building material was as follows: Cement > quarry dust > bagasse ash from sugarcane. After XRD analysis confirms that the crystallite size of sugarcane bagasse ash is lower than that of other building materials therefore its compressive strength performance is more [47,48]. ...
India is one of the countries with the strongest agricultural production, hence leading to accumulation of the wastes and therefore leading pollution to the environment. Researchers are using different methods for using this agricultural and industrial waste by-products for construction purposes to safeguard natural sources like limestone, and river sand. By utilizing these materials in the construction sector, the material cost can be brought down to some extent and it also helps the environment to be free from pollution. This research paper object to the usage of Sugar Cane Bagasse Ash (SCBA) (Agricultural Waste) and Quarry Dust (Q.D) (Industrial Waste) as a partial substitution for cement and sand respectively to reduce the scarcity of the limestone and river sand. SCBA was replaced with cement in different levels of replacements 5%, 10%, 15%, 20%, 25%, 30%, 35%, and 40% respectively. The different tests were done to find out the performance of the concrete and the results were compared with the conventional mix. SEM analysis was done to find out the particle dimensions and composition of the materials. The compressive strength of the specimens was increased upto the level of 35% and then it was noticed that the strength got decreased. The content of SCBA got decreased beyond 35% due to the material characterization and relatively more voids in the preparation of concrete specimens, resulting in the reduction of density of concrete. So that the test results are proven that the SCBA can be replaced by 35% (Optimum level).
... Mohajeri [20] model. Meany recent reaches studied progressive collapse experimentally, numerically and analytically [21][22][23][24][25][26]. Through the comparison, it is clear that the laboratory results are close to the proposed analytical results by the two models. ...
This paper is mainly composed of a comprehensive evaluation and discussion on the progressive collapse performances of outrigger braced reinforced concrete structures with transfer floor. The effects of transfer floor existence, combined use of transfer floor and outriggers, outrigger locations on load redistribution, plasticity development and robustness of structural systems under the sudden failure of the element(s) are the fundamental issues that shape the content of this study. Within this scope, six reinforced concrete systems with transfer floor and differently located outriggers are modelled in SAP2000 finite element program. The pushdown curves are compared through the nonlinear static analysis. For external and corner column cases, the maximum load factors versus vertical drift ratios are obtained in systems with outriggers located at the midheight (0.5H) and top level (H), especially. The differences in deformation characteristics of transfer floor-element interface can be properly limited by modifying outrigger locations and combinations. The hinging development can be much more effectively controlled with outriggers close to the transfer floor. The same tendency is also observed while the vertical spacing between outriggers is decreased, particularly until 0.65H. The results support that the optimized outrigger use develops an efficient alternate load paths under the abrupt element failure.
One static and four dynamic collapse experiments have been conducted on beam-column assemblies under a middle-column removal scenario to investigate the dynamic collapse responses. All the assemblies had identical configurations, materials, and boundary conditions. Numerical analyses were conducted for an in-depth comprehension of different behaviors of the assemblies under static and dynamic collapse scenarios. To ease the assessment of the dynamic collapse responses of the beam-column assemblies, a new assessment procedure was proposed based on the energy-method and was proved to be efficient and accurate by comparing with the experimental and numerical results. Research indicated that the dynamic collapse behaviors of the assemblies were influenced by two key factors, i.e., the dynamic stress distribution characteristics and the material strain rate effect. Under the dynamic collapse scenario, the structural resistance of the assemblies was impaired during the stage of compressive arch action (CAA) due to the dynamic stress distribution characteristics. Whereas the material strain rate effect could enhance the resistance in the stage of the catenary action (CA). Moreover, both factors contributed to increasing the largest deformation of the assemblies. The dynamic amplification factor (DAF) was also evaluated based on the proposed assessment procedure and the traditional one. At the critical deformations during the CAA and CA stages, the DAFs obtained through the proposed procedure were found to be greater than those determined by the traditional procedure in which the dynamic stress distribution characteristics and the material strain rate effect were both neglected. Further, the DAFs suitable for practical engineering design were also discussed.
This paper investigates the behaviour of a reinforced concrete beam under a support removal. A detailed parametric analysis is carried out, covering the effect of support removal rate on dynamic response. The linear elastic and nonlinear inelastic responses are computed and studied in detail. Critical parameters during the structural response are identified. In order to determine the ultimate load, the vertical pushover analysis is performed. The key parameters driving the beam response are assumed as random variables, and respective reliability study makes it possible to check the overall uncertainty of the dynamic response. In particular, the response spectrum measuring the effect of support removal rate has been computed. It has been demonstrated that the critical vertical response occurs when the time of support removal is up to to 17% of the first natural period. The vertical pushover analysis results in obtaining capacity curves and showed the order in which two plastic hinges occur for various load patterns. Finally, the reliability-based sensitivity analysis indicates the geometric cross-section cover and height are the most sensitive parameters of the beam response.
Explosions caused by standoff charges near buildings have drastic effects on the internal and external structural elements which can cause loss of life and fatal injuries in case of failure or collapse of the structural element. Providing structural elements with blast resistance is therefore gaining increasing importance. This paper presents numerical investigation of RC columns with different reinforcement detailing subjected to near-field explosions. Detailed finite element models are made using LS-DYNA software package for several columns having seismic and conventional reinforcement detailing which were previously tested under blast loads. The numerical results show agreement with the published experimental results regarding displacements and damage pattern. Seismic detailing of columns enhances the failure shape of the column and decrease the displacement values compared to columns with conventional reinforcement detailing. Further, the effect of several modeling parameters are studied such as mesh sensitivity analysis, inclusion of air medium and erosion values on the displacements and damage pattern. The results show that decreasing the mesh size, increasing erosion value and inclusion of air region provide results that are very close to experimental results. Additionally, application is made on a slab-column multistory building provided with protective walls having different connection details subjected to blast loads. The results of this study are presented and discussed. Use of a top and bottom floor slab connection of protective RC walls are better than using the full connection at the four sides to the adjacent columns and slabs. This leads to minimizing the distortion and failure of column, and therefore it increases the chance of saving the building from collapse and saving human lives. Doi: 10.28991/cej-2021-03091733 Full Text: PDF
The progressive collapse resistance of reinforced concrete (RC) and precast concrete (PC) buildings has become a rising concern in recent years. Extensive research has been conducted to investigate the structural response of framed concrete structures after the local damage of single or multiple structural components. Being essential components in buildings, slabs play a crucial role in mitigating the progressive collapse of structures. This paper presents a comprehensive review of current research on the slab performance in RC and PC structures to resist progressive collapse. The structural resistance mechanisms exhibited by the slabs during a collapse event is discussed in detail. A database of experimental research on RC beam slab and RC flat plate substructures is collated and compared. Moreover, factors affecting progressive collapse resistance of RC structures, such as loading configurations, boundary conditions, reinforcement ratios, slab thickness and dynamic effects are discussed. The retrofitting techniques proposed in the literature to mitigate progressive collapse are also reviewed and some design proposals are suggested.
The concrete elements undergo major physical and chemical changes when it gets in contact with high-temperature. The thermal effect will allow concrete elements to lose their strength and other structural parameters. In the case of reinforced concrete structural frame system, when reinforced concrete key elements undergoes thermal changes due to high-temperature, it leads to a major collapse as they are load-carrying elements. So, the key members of reinforced concrete structural frame must be analysed under high-temperature to understand their behaviour. In this study, a single-bay single-storey three-dimensional reinforced concrete prototype frame was analysed under high-temperature conditions using ABAQUS. A comparative study was made from the behaviour of reinforced concrete frame with slab and infill wall under high-temperature condition. The inclusion of slab and infill wall to the structural frame can improve the stiffness and overall structural performance. The major findings such as axial load, deformation, stiffness of the frame, bending moment and shear force can obtained from this analytical study.
Many negative factors can influence the progressive collapse resistance of reinforced concrete (RC) frame structures. One of the most important factors is the corrosion of rebar within the structure. With increasing severity of corrosion, the duration, robustness, and mechanical performance can be greatly impaired. One specific side effect of rebar corrosion is the significant loss of protection against progressive collapse. In order to quantify the effects of rebar corrosion on load-resisting mechanisms (compressive arch action (CAA) and tensile catenary action (TCA)) of RC frames, a series of numerical investigations were carried out in this paper. The previous experimental results reported in the literature provide a benchmark for progressive collapse behavior as a sound condition and validate the proposed numerical model. Furthermore, based on the verified numerical model, the CAA and TCA with increasing corrosion and an elapsed time from 0 to 70 years are investigated. Comparing with the conventional empirical model, the proposed numerical model has shown the ability and feasibility in predicting the collapse resistance capacity in structures with corroded rebar. Therefore, this numerical modeling strategy provides comprehensive insights into the change of load-resisting mechanisms in these structures, which can be beneficial for optimizing the design.
Collapses or serious damages of existing buildings during strong earthquakes have resulted in significant economic losses, severe injuries and loss of human lives. Given the late introduction of modern seismic standards and the large number of the existing under-designed buildings, the scientific interest has progressively been focusing on developing techniques for the seismic upgrading of existing buildings. The present paper aims at providing a review of the seismic upgrading techniques, which target reinforced concrete (RC) buildings, as such buildings constitute a large portion of the existing building stock. The retrofitting methods are divided into two distinct categories: the local measures, which enhance the behavior of individual elements and the global ones, which operate on the structure as a whole. Both traditional and novel techniques will be discussed, but the latter will be emphasized.
The issue of progressive collapse of two real-scale frame buildings examples (three and six stories) constructed from High-Strength Concrete (HSC with fc` =75 MPa) and Normal-Strength Concrete (NSC with fc` =32 MPa) under central column removal have been studied using numerical analysis. Initially, a finite element linear static analysis was carried out. Next, linear dynamic and non-linear dynamic analyses were conducted to account for the extreme dynamic effects that arise during central column removal. The values of Demand-Capacity Ratios are considered in each analysis. The results showed that, the analysis of progressive collapse under central column removal of three and six stories frame buildings constructed from HSC is approximately similar to that of the same structures constructed with NSC. The three stories building constructed from NSC and HSC would not be susceptible to collapse for linear statically central column removal, while the situation is reversed for both NSC and HSC six stories buildings. NSC and HSC three and six stories buildings would be susceptible to progressive collapse for linear and nonlinear dynamic central column removal. The ratio between the maximum nonlinear dynamic displacement and the maximum linear dynamic displacement for NSC and HSC three stories buildings at the column removal are 1.17 and 1.18, respectively, whereas these ratios become 1.89 and 1.86 for NSC and HSC six stories building, respectively. The internal forces at the most critical sections for NSC and HSC three story building in the case of linear dynamic analysis are larger than that of linear static analysis by about 58% and 39%, respectively, while for six story building these ratios become 82% and 80%, respectively. For the case of nonlinear dynamic analysis, these ratios for NSC and HSC three story building are larger than that of linear dynamic analysis by about 9% and 7%, respectively, while for six story building these ratios become 11 % and 8%, respectively due to activation of plastic hinges.
Due to the repetitive progressive collapse events, it became necessity to form theories of designs against those cases of loadings. Prestressed reinforced concrete elements become widely used in construction field due to various properties that contribute to enhancing the overall structural stiffness, increasing the loading capacity, and elevating the crack resistance threshold compared to the non-prestressed elements. However, few researches in prestressing members and its capacity towards progressive collapse is covered. According to the Unified Facilities Criteria (UFC) and the General Services Administrations (GSA) guidelines, the pre-stressed precast structure's assessment under progressive collapse are taken into consideration using approximate solutions for analysis. The UFC stated the types of the structure under progressive collapse assessment regardless of the structural system used. This is a great challenge needs a lot of experimental and numerical testing and validation. In this research, a numerical analysis is carried out for a typical five-story framed prestressed precast reinforced concrete structure subjected to column loss (corner column, edge column and internal column near to the structure's edge), and designed according to Precast/Prestressed Concrete Institute (PCI) and (ACI 318À14). Non-linear dynamic analysis for the structure was carried out using Extreme Loading for Structures (ELS) software depending on the AEM. The investigation was done on two levels. Total collapse took place in case 1. As a result, the necessity of extending the research to include case (2) is essential for having an overview assessment of this type of structures. Case 2 showed high capability to resist progressive collapse against all column removal scenarios. The results are indicated in terms of; prestressed beam behavior, prestressing cable contribution, and flexure and axial loads' changes with respect to time. Beam and column rotations are calculated and compared to the UFC limitations to assess its safety towards progressive collapse.
This paper investigates the influence of perforated masonry walls on the progressive collapse resistance of multi-story reinforced concrete (RC) structures. In this study, bare and infill-wall RC frames are studied by considering column failure at corner and exterior locations. Infill-wall panels are simulated by using equivalent compression struts and their provision of alternate load paths under the removal of a critical load-bearing element is examined. Linear static, nonlinear static, and nonlinear dynamic analyses are conducted by following the General Service Administration (GSA) guidelines. The analysis results show that the infill walls are beneficial in the redistribution of loads after the failure of the column and the collapse resistance of the RC building is increased. Empirical dynamic amplification factors (DAF) are also calculated in the sequel and the factor instructed in the GSA guidelines is judged by comparing with these computed dynamic factors. The results show that the DAF of 2, recommended by the GSA guidelines, is conservative and the presence of infill walls does not significantly affect the value of DAF.
Throughout the past decades, failure of structures threatening the lives of humans had been popular whether through structure failure due to human error such as Hyatt Regency walkway collapse, 1981, terrorist attacks on the American embassy attack in Nairobi, Kenya 1998 and the famous 9/11 attacks in 2001 and many more. As a result of these incidents, The Unified Facilities Criteria (UFC) was developed concerning the progressive collapse issues by analyzing different types of structures under column loss and studying the overall structural behavior. However, the (UFC) didn’t scope on the local behavior of the structural components and its connection under column loss. In this research, the main objective is to study the local behavior of the special moment frame connection (SMC) under column loss. A detailed study is conducted on a 3D model fully designed by adopting the strong-column weak-beam approach following the ACI318-14 regulations. Two frames are selected from the designed structure, interior and exterior frames, to apply the column loss scenario in different locations and different floor levels. The Applied Element Method is adopted in the study. Non-linear time-dependent dynamic analysis is implemented to apply the different column removal scenarios. Twelve case studies are modeled in detail using the Extreme Loading for Structures (ELS) software at which all elements are modeled and analyzed in a 3D model technique. After analyzing the different case studies, structure behavior is observed. Some cases encountered total collapse, other cases encountered partial /local collapse and finally, some survived the column loss scenario. Many parameters are involved and studied in the research. Failure pattern is observed for collapsed cases, the cause of failure is monitored and studied. Special moment connection behavior is studied concerning the shear connection capacity. The location of the column removal with the type of frame selected played an important role in changing the structural behavior from one case to another. As a result, it is not applicable to assume that due to the special moment connection ductility, the structure will be able to resist the column loss in all cases.
Column removal failure is a common failure type of reinforced concrete (RC) structures subjected to progressive collapse. Thus, it is widely adopted to use the experimental/numerical column removal scenario to assess the progressive collapse capacity of RC structures. However, most of existing studies neglect the uncertainties involved in the structures, e.g., geometric size and material properties, while it may have great influence on the overall behavior of the structure under progressive collapse. In this paper, a probabilistic analysis of RC beam-column sub-assemblage under column removal scenario is performed. An efficient numerical model based on the finite element software OpenSEES is firstly developed for progressive collapse analysis of RC structures. The model adopts fiber beam-column element with co-rotational formulation to simulate the extreme behavior of frame members under column removal scenario, and uses a Min-Max material to apply the material failure criterion. Then the probability density evolution method (PDEM) is employed to conduct the probabilistic failure analysis. Two benchmark column removal tests of RC sub-assemblages are selected as the numerical case study examples. The deterministic analysis results indicates that the proposed finite element model is effective to reproduce the typical behavior of the sub-assemblages, while the probabilistic analysis provides mean values, standard variations and probability density functions (PDFs) of the whole progressive collapse process. Finally, the influence (or sensitivity) of the uncertain parameters on the global and local behaviors of RC beam-column sub-assemblage under column removal are quantified.
External installation of steel braces has been proved an effective seismic strengthening or retrofitting scheme to upgrade the lateral load-resisting capacity of reinforced concrete (RC) frames. However, the effectiveness of steel bracing in improving the progressive collapse resistance potential of RC frames is vague. To fill the gap, five one-quarter-scaled specimens (one bare frame and four braced frames) were tested subject to a pushdown loading regime. The RC frames were nonseismically detailed for reference. Four braced frames with different bracing configurations were tested to evaluate the efficiency of braces for upgrading the load-resisting capacity of RC frames. A rational design method was implemented for designing the braced frames, including the connections between the braces and RC frames. Experimental results proved that steel bracing could increase the first peak load and initial stiffness of the frames significantly. Before mobilization of catenary action in RC frames, the tensile braces were fractured, but the compressive braces experienced severe buckling. Consequently, the braced specimens performed similarly to the bare frame in the catenary action stage.
Progressive collapse is a catastrophic partial or total failure of a structure that mostly occurs when a structure loses a primary component like a column. Some international standards have started to consider progressive collapse resistance in various approaches. In this study, the ‘Unified Facilities Criterion’ guidelines were used in assessing the structure; these guidelines represent one of the codes that discuss progressive collapse using sophisticated approaches. Three-dimensional nonlinear dynamic analyses using the ‘Applied Element Method’ were performed for a structure that lost a column during a seismic action. A parametric study was made to investigate the effect of different parameters on progressive collapse. In this study, a primary structural component was assumed lost during an earthquake. The studied parameters were the location of the removed column in plan, the level of the removed column, the case of loading, and the consideration of the slabs. For the study cases, it was concluded that the buildings designed according to the Egyptian code satisfies the progressive collapse requirements stated by ‘Unified Facilities Criteria’ (UFC) guidelines requirements with a safety factor of 1.97. Also, it was found that losing a column during a seismic action is more critical for progressive collapse than under gravity load. Finally, this study elaborated the importance of considering the slab in progressive collapse analysis of multistory buildings in order to include the significant catenary action developed by the slabs.
Flat slab system is becoming widely popular for multistorey buildings due to its several advantages. But performance of flat slab buildings under earthquake loading is unsatisfactory due to its vulnerability to punching shear failure. Several codes provide the guidelines for deigning flat slab system under gravity load only. However flat slab buildings are also being constructed in high seismicity region which can cause collapse of the buildings under seismic loading. In this paper, performance of flat slab buildings designed as per existing code guidelines have been evaluated under earthquake loading. This study is carried out on a five and a ten storied buildings with identical plan. These buildings have been designed as per guidelines of Indian code, ACI code, Eurocode and New Zealand code. Nonlinear static analysis has been carried out to evaluate the performance of these buildings with and without considering the continuity of slab bottom reinforcement through column cages. Equivalent frame approach with transverse torsional members has been used to model these flat slab buildings. From the results of nonlinear analysis it is clear that most of the buildings are not ensuring CP performance for MCE level of hazard in high seismicity areas. Continuity of slab bottom reinforcement has an influence on performance of flat slab buildings. It improves the performance of the buildings. Maximum inter-storey drifts of the buildings at collapse have been compared with the limiting value of maximum inter-storey drifts corresponding to gravity shear ratio, given in literature. It is found that most of the buildings analyzed here are collapsing at an inter-storey drifts lower than that prescribed in literature.
The nonlinear static response of a vertically oriented coupled wall subjected to horizontal loading is presented in this research article. The 3 storey vertically oriented coupled wall interconnected with coupling beams is modelled as solid elements in a finite element (FE) software named Abaqus CAE and the steel reinforcement is modelled as a wire element. For simulation of concrete models, a concrete damaged plasticity constitutive model is taken into consideration in this research. Moreover, with the help of concrete damage plasticity parameters, validation of two rectangular planar walls was executed with an error of less than 10 percent. Finally, these parameters are used for modeling and analyzing the static behavior of coupled walls connected with coupling beams. Furthermore, the maximum unidirectional horizontal loading helped in obtaining the compression and tensile damage as well as scalar stiffness degradation. Significantly, the research also found the plastic hinge location in the coupled wall as well as in the coupling beam, which are of utmost importance in nonlinear analysis. Doi: 10.28991/HIJ-2022-03-02-010 Full Text: PDF
The efficiency of combining fine aggregate's (sand) partial replacements with waste crumb rubber (CR) and steel fiber (SF) has been investigated in this paper. The study aims to enhance the RC frame's deformability, as well as its structural ductility to achieve progressive collapse resistance. To this end, a total of four RC frames' behavior at one-third scale under a situation of a middle-column removal was experimentally tested. Two frames were made of 0% CR and SF. Another two frames were made by incorporating CR at 20% by volume for the sand replacement and 0.5% SF fraction volume. The findings of the study reported an enhanced structural ductility, which was stimulated by incorporating CR and SF in normal concrete. The tested steel fiber-reinforced rubberized concrete frames, however, showed further deflection by 29.5% compared with the conventional frames.
The present study is focused on the compressive strength, water retention, and workability by varying the percentage of poly ethylene glycol 200 and liquid paraffin wax from 0% to 1% by weight of cement for self‐compacting concrete and compares it with conventional SCC. Percentages of 0.1%, 0.5%, and 1% (in proportion to the weight of cement) were adopted in the study. The comparison was done in a grade concrete and with cases such as indoor curing and water‐based curing. Slump‐flow test and V‐funnel tests were carried out on the fresh concrete to evaluate the workability of concrete. Concrete weight loss with time is evaluated to determine the water retention capacity. Compressive strength of cube specimens was conducted at the end of 7 and 28 days of curing. The durability of the concrete was assessed by immersing the concrete specimens in acids. The fresh properties were satisfied according to EFNARC specifications. Based on the weight loss percentage and satisfaction of compressive strength, the dosage of a self‐curing compound was determined. XRD analysis of the concrete was also performed on the concrete specimens.
To examine high-rise building robustness to sudden column removal, progressive collapse studies of a 13-story flat-slab reinforced concrete (RC) core-wall building system were completed in this study. Two buildings on the University of Nebraska-Lincoln (UNL) campus, Cather and Pound Halls, were demolished in December of 2017. UNL researchers were given unique access to the building sites to assess their response before, during, and after the event. Prior to demolition, accelerometers were placed throughout both buildings, and ambient measurements were conducted to establish natural frequencies and mode shapes. The response of both buildings during controlled demolition was recorded and analyzed using time histories from the accelerometers. Controlled demolition initiated with sequential blast detonation at selected column sections that resulted in progressive collapse. A detailed 3D nonlinear numerical model of Pound Hall was developed using LS-DYNA to mimic the progressive collapse. The accuracy of the building model was evaluated via comparisons between (i) simulated and measured building ambient frequencies and modes; and (ii) displacement and video recorded during the full-scale demolition. The validated model was then used to further investigate damage scenario effects on the robustness of high-rise RC buildings caused by sudden removal of columns at various locations on the ground floor. The study results can be used to develop and calibrate the nonlinear numerical model for analyzing high-rise building progressive collapse behavior and can help provide information that may improve new and existing flat-slab RC core-wall building robustness against progressive collapse.
The field of progressive collapse has attracted considerable attention worldwide, while little existing building structure has been constructed with progressive collapse design. Therefore, some researchers began to explore effective strengthening methods to improve the progressive collapse resistance of existing building structures while saving cost, resources, and time. In this paper, two 1-bay-by-2-bay two-story reinforced concrete (RC) frames with the loss of one edge column were constructed and tested, including the control and strengthened specimens. The strengthened specimen was strengthened with high-performance ferrocement laminate and bonded steel plates to investigate the strengthening effectiveness. Based on the data collected during the experiment and simulated results, crack development patterns, load-displacement relations, lateral deformation, load distribution, and the effect of strengthening were discussed. Additionally, the finite-element (FE) simulation and the theoretical analysis for such structure were implemented. The results show that the initial stiffness and bearing capacity of frame increased after strengthening. Increasing the steel strand quantity, the peak load can be significantly increased. The stiffness in different floor will have an effect on the load bearing distribution. Higher stiffness in floor will bear much vertical load. The axial compression on adjacent columns increased while decreased in the diagonal columns. The contribution to bearing capacity of slab is weaker than beams. The slab could share about 2/3 vertical load of beams for control specimens and less than 1/2 vertical load of beams for strengthening specimens.
Since existing precast RC (reinforced concrete) structures are lacking structural continuity at regions of beam-column connections, they are less resistant to progressive collapse in the event of column removal than CIS (cast-in-situ) RC structures. The prime objectives of current research are to revise the existing precast simple shear beam-column connections and to develop new precast moment connections for increasing the progressive collapse robustness of precast buildings. To achieve these goals, 11 half-scale beam-column assemblies – comprising two beams and three columns – were numerically investigated under the middle column removal scenario using nonlinear 3D FE (finite element) modeling. Two specimens represented typical existing precast simple beam-column connections, and three specimens had revised precast simple connections. Four assemblies were designed with new precast moment connections. The last two specimens represented CIS concrete beam-column connections with continuous and discontinuous longitudinal beam bars to be compared with the precast assemblies. The FE modeling incorporated strain rate-dependent nonlinear constitutive models, contact between different parts in the connection region, and bond-slip at steel bars-to-concrete interface. As a key outcome of this research, the newly developed precast moment connection with the highest rotational ductility was recommended for diminishing the potential of progressive collapse in precast concrete buildings.
In this study, the performance of viscoelastic dampers designed for seismic loading has been investigated for controlling reinforced concrete special moment frame (RC-SMF) structures against blast loading. In addition, the progressive collapse due to an explosion has been examined in these structures. Three reinforced concrete structures with three, six, and fifteen floors have used for this study. All three structures have special moment frame as the lateral resisting system and were equipped with seismic viscoelastic dampers. The attained results confirmed impact of the seismic viscoelastic dampers d in reducing the response of structures to blast loading, especially in low rise structures and lower floors of high rise structures. In the investigation of progressive collapse, in order to specify the most critical column under the blast loading applied on structures, a new method was introduced in addition to the column's elimination scenarios introduced in the USGSA code. This study introduced a new method for specifying the most critical column under the blast loading. The attained results from this method compared with columns elimination scenarios that discussed in the USGSA code. In this developed method, the critical columns which with the maximum generated strain in the longitudinal rebar of the column eliminated and the structures reanalyzed for progressive collapse. After the elimination of the desired column, a progressive collapse analysis was performed. According to the results of the sudden removal of the column and the nonlinear dynamic analysis, the collapse would occur with and without dampers in the case of the 3-story building, in the case of the 6-story building there is an improvement in the vertical displacement and in the case of 15- story the difference is not significant.
The progressive collapse behavior of conventional reinforced concrete frame structures caused by the loss of columns has been widely investigated over the past years. However, few papers on the improvement of the structural progressive collapse resistance accounting for the mechanical properties of the reinforcement material are reported. As a kind of reinforcement material of reinforced concrete frames, steel-FRP composite bar (SFCB) has the typical feature of controllable post-yield stiffness. This paper explored and compared the progressive collapse characteristics of concrete frames reinforced with SFCBs, steel bars and hybrid reinforcements including both steel bars and FRP bars. Scaled pushdown experiments based on the alternate load path method were conducted to study the effect of post-yield stiffness on the progressive collapse resistance of beam-column sub-assemblages. The experimental results demonstrated that the SFCB specimens experienced three mechanical actions: flexural action, post-yield stiffness plus compressive arch action (PYSCAA) and catenary action. The feature of the PYSCAA differed significantly from the second action of the specimen reinforced with steel bars. Due to the effect of the post-yield stiffness, not only was the load capacity of SFCB specimens significantly enhanced, but also the transition displacements from the PYSCAA to the catenary action were delayed. Meanwhile, the finite element method was employed to simulate the whole progressive collapse process of the specimens, and the simulation results agreed well with the experimental ones. Parametric analyses based on numerical simulations proved that the application of SFCBs was beneficial to reduce the vulnerability of progressive collapse for concrete frames. The ratio of post-yield modulus to initial elastic modulus of SFCBs was found to be the key factor affecting the characteristics of the progressive collapse resistance, and the optimal ratio of 0.30 is recommended.
The problem of progressive collapse has been a major topic in structural forensic engineering since its inception, but it has recently received a growing interest. In the last two decades, the occurrence of extreme events and their catastrophic impact on the built environment and people has promoted several research programmes and guidelines for structural design and assessment, spotlighting the importance of back-analysis and numerical prediction of progressive collapse phenomena. This paper presents a numerical study aimed at investigating the ability of existing reinforced concrete structures to prevent progressive collapse during structural retrofitting. The progressive collapse capacity of a real, reinforced concrete framed building constructed in the 1950s and partially collapsed in 2001 is discussed in relation to a couple of structural retrofitting operations that were found to be the primary causes of the accident. Existing information from past forensic investigations was integrated with a simulated design procedure to develop the capacity model of the structure, according to design codes and practice rules used at the time of construction. Nonlinear pushdown analysis with displacement control was carried out both in intact conditions and during retrofitting operations. In addition to global capacity models of the structure, the use of partial capacity models representing the building corner under retrofitting was evaluated, highlighting a very high computational efficiency of those simplified models. Analysis results also indicate that the load contribution from infill walls can significantly influence the progressive collapse resistance, particularly in relation to retrofitting works involving the corner of the building plan as actually happened. Retrofitting interventions on the real building included the concrete cover removal from ten ground-floor columns and soil excavation around column bases. The removal of concrete cover from single and multiple ground-floor columns together with the loss of supports due to soil excavation around column bases was found to significantly affect the collapse capacity of the structure. The major impact of retrofitting operations in terms of location and extent provides a simulation-based proof of the progressive collapse suffered by the case-study building, evidencing that soil excavation around more than three columns was able to produce the accident.
This paper uses an innovative algorithm combining machine learning as a decision-maker (DM) and Particle Swarm Optimization (PSO), called DMPSO, as a structural optimization technique, to design reinforced concrete frames for progressive collapse employing the alternate path method. In the alternate path method, multiple scenarios of removing critical elements should be considered, which makes the design process extremely repetitive and costly. Therefore, the development of an optimization technique is beneficial for producing efficient and cost-effective design solutions. The effectiveness of the proposed optimization algorithm is illustrated in optimization of a reinforced concrete structure that is subjected to lateral seismic forces, while the design concurrently satisfies both the American Concrete Institute provisions and the Unified Facilitates Criteria progressive collapse requirements. The results confirm the ability of the proposed DMPSO algorithm to efficiently find optimal design solutions in reinforced concrete structures that are subjected to progressive collapse.
The progressive collapse of buildings could result in significant financial losses and casualties, and it is therefore of the utmost importance to reduce the risks of such occurrences. Flat-slab buildings are much more prone to progressive collapse than moment-frame buildings, since as there are no beams for redistributing the loads that the lost column initially resisted. Even more consideration should, therefore, be given to assessing the progressive collapse of flat-slab buildings. The current analytical research assesses the progressive collapse behaviour of eight-storey R.C flat slab building, with and without perimeter beams, by conducting linear static progressive collapse analysis as per the GSA guidelines (2016). This research explores the column removal situations for various typical positions on each storey, unlike earlier studies where only certain typical columns on the first storey are removed. The results are analyzed for each scenario in terms of joint vertical displacement and chord rotation at column removal locations, and thus the susceptibility of the building to progressive collapse is calculated in compliance with the relevant accepted criteria laid down in the DoD Guidelines (2009). The results showed that the incorporation of perimeter beams in flat slab buildings improved the progressive collapse resistance as it reduces joint displacement and chord rotation at column removal locations by providing sufficient stiffness and load paths for increased gravity loads.
Compared to monolithic reinforced concrete (RC) buildings, precast RC buildings are more prone to the risk of progressive collapse. Therefore, there is a need for efficient methods to strengthen beam-column joints in existing precast structures for mitigating the progressive collapse. This paper studies numerically using the finite element (FE) method the risk of progressive collapse of precast concrete beam-to-column connections rehabilitated with steel plates under middle column-loss event. Nonlinear FE models were established with the help of LS-DYNA software for predicting the response of both unstrengthened and strengthened precast RC single story two-bay frames under middle column-loss event. The developed FE models consider material nonlinearity – including strain-rate effect – for concrete, steel rebars, rubber pads and steel plates; in addition to contact behavior between different members in the joint region. The models were validated using the data of three half-scale frames tested under middle column-loss event. Specimens involved: one control unstrengthened precast RC frame, one monolithic assembly with continuous beam rebars, and another precast assembly alike the control frame but rehabilitated utilizing steel plates in joint region. The calibrated FE modeling was employed for parametric studies of practical interest wherein the influence of steel plate parameters was studied.
The choice of the most suitable constitutive models for fibre-based progressive collapse analysis of reinforced concrete (RC) structures is still an open issue, mainly because nonlinear material modelling has never been treated as a variable involved in the assessment problem so far. To support analysts in selecting which models could be more representative of the actual inelastic material response for progressive collapse analysis of RC framed buildings, this paper presents a numerical investigation where fibre modelling was integrated with different combinations of stress-strain relationships for concrete and reinforcing steel. A series of pushdown simulations of a two-bay perimeter frame mock-up were then carried out to assess the gravity load capacity under downward displacement. Analysis results are compared with available experimental test data for performance quantification of numerical models, which is based upon an experimental-to-numerical load capacity ratio and overall statistical parameters. Sensitivity to the material modelling approach, load eccentricity and boundary conditions is evaluated, involving strain indicators that can be used in performance-based robustness assessment of RC framed buildings. Finally, a number of parametric analyses are presented to show how the load capacity is influenced by capacity model properties, such as material strengths, beam span length, and span length ratio of asymmetric frames.
Precast concrete (PC) frames are considered vulnerable to progressive collapse as inadequate ties between precast components can lead to a loss of structural continuity. In previous studies, slabs and masonry infill walls were found able to mitigate the progressive collapse behaviours of reinforced concrete (RC) frames. However, progressive collapse physical tests of PC frames with prefabricated concrete infill walls are scarce. Therefore, laboratory tests of three PC specimens, including bare frame, semi-infilled frame and fully infilled frame, are conducted in the paper under a centre column loss scenario. Reinforcement detailing and specimen setup are introduced and recorded results are discussed. Observations during test indicate that failure of the PC bare frame is governed by the pull out of anchorage bars at the beam-exterior column joint. Moreover, the infilled specimen leads to a substantial increase in load-carrying capacity at both the flexural stage and catenary action stage when compared with the bare frame. Based on numerical simulation, it can be concluded that the size and position of the opening have a significant impact on structural resistance of an infilled PC frame, especially on the resistance at the flexural stage.
The progressive collapse of reinforced concrete (RC) structures is a structural failure caused by abnormal loads. It starts as a local failure, followed by a sequential reaction that may result in massive portion failure or even progressive collapse of the entire structure. The collapse of the Ronan Point Apartment in England in 1968 resulted in increased interest in structural integrity and resistance to progressive collapse. Given the large economic losses and extensive casualties, researchers began to conduct studies that would advance the understanding of the behavior of structures under column removal scenarios. This paper summarizes previous studies on the progressive collapse of RC structures and focuses on experimental studies on various types of structures, such as beam–column and beam–slab sub-assemblies, planar frame structures, and large-scale buildings. Numerous aspects, including (1) general overview; (2) progressive collapse resistance mechanisms; (3) review of previous experimental tests in terms of alternate load path approach, types of testing procedure, the effects of boundary conditions, additional reinforcing rebars, seismic detailing, structure retrofitting, infilled walls, contribution of RC slabs and transverse beams, demolished building, multi-hazard, new mitigation schemes for precast frames, and alteration of concrete mixture materials; and (4) discussions and concluding remarks, are presented in a summarized, comprehensive, up-to-date manner. This work helps researchers, professionals, and experts understand the behavior of different structural systems and new mitigation schemes that have been utilized in literature to develop progressive collapse resistance experimentally. Consequently, gaps and weaknesses points can be addressed in future studies.
Existing research studies have primarily examined the progressive collapse of frame structures under an inner column removal scenario. However, progressive collapse risk is much higher when penultimate columns close to the structural periphery are damaged due to weaker horizontal constraints. A static progressive collapse test was thus conducted in this study on two single-story beam-column planar substructures with flange slabs, in which a penultimate and an inner column were removed respectively. Compared to the specimen with an inner column removal, the specimen with a penultimate column removal exhibited a larger vertical displacement under the small deformation stage, which further reduced the contribution of the compressive arch action to the collapse resistance. Under the large deformation stage, the resistance of the specimen with an inner column removal increased significantly, while that with a penultimate column removal was not enhanced notably because the horizontal movement of its edge column resulted in a smaller rise of steel strains under the catenary action. The internal forces were calculated using the measured strain data at the key sections of the slab-flange beams. The calculated results also confirm that the compressive arch action and catenary action were unable to be fully developed in the specimen with a missing penultimate column. Finally, the outcome of the vulnerability assessment of the prototype reinforced concrete frame reveals that there might be a potential risk of progressive collapse to the structure under large deformations when a penultimate column on the ground floor is damaged and the risk is higher when a penultimate column on the top floor is damaged.
Although many existing damage diagnosis techniques based on the combination of optimization algorithms and finite element model updating have been studied and demonstrated to be promising, there are still some limitations that need to be improved to enhance their performance for the large and complex structures. In this regard, the present article proposes a FE model updating technique based on the existing commercial software SAP2000-OAPI and an enhanced symbiotic organisms search (ESOS) algorithm for damage assessment of full-scale structures. First, to overcome the complexities of FE simulation, the FE model of monitored structure is built in SAP2000 software for analyzing the dynamic behavior of the structure. Then, the damage assessment of the structure is set up in the form of an optimization problem in which the objective function is established based on a combination of flexibility matrix and modal assurance criterion (MAC). An improved version of SOS algorithm, called ESOS algorithm, is adopted to solve this optimization problem for detecting and quantifying any stiffness degradation induced by damage. To perform the iterative optimization task automatically, a link between MATLAB and SAP2000 is created by using the OAPI feature of SAP2000. Finally, the numerical investigations on two full-scale structures with considering measurement noise and sparse measured data demonstrate the feasibility of the proposed technique in predicting the actual damage sites and their severities.
This paper discusses on the efficiency of partial replacements of fine aggregate (sand) by waste crumb rubber for improving the deformability and structural ductility of the reinforced concrete (RC) frame and thus resisting progressive collapse. This research experimentally tested the behaviour of four RC frames at one-third-scale under the middle column removal scenario. For comparison, two frames were prepared for 0% crumb rubber as the controlled specimens. The remaining frames were prepared for 20% crumb rubber replacements by volume for sand. The mechanical properties, failure mode, the crack pattern, the load-displacement behaviour, and structural ductility are analysing herein for normal and RuC frames. Results indicated that there was enhanced in structural ductility induced by the addition of crumb rubber in conventional concrete. Meanwhile, the RuC frames showed more deflection than the NC frames. Therefore, RuC is an eco-friendly building material that can be used for enhancing the ductility of RC elements as a new design strategy for preventing progressive collapse.
In practice, infilled frame is a common structure but the contribution of infill walls is typically ignored in previous research on progressive collapse. To this end, numerical models based on solid-element are employed to investigate the behavior of reinforced concrete (RC) frames with concrete masonry infill walls under a middle column removal scenario (CRS). The numerical models of bare and infilled frames are initially validated through previous experimental results. Then the numerical models are used to illustrate the effects of infill walls on the load transfer mechanisms of the frames under a CRS and the interaction between infill walls and frame members. Thereafter, the size effect of the frame models is discussed and the numerical models are further extended to study the effects of pertinent geometric parameters on the progressive collapse behavior, including the height of partial-height infill walls, the opening position and area of wall panels as well as the number of stories. The results indicate that the load transfer mechanism of a two-story infilled frame in a middle CRS is the frame action provided by frame members and the truss mechanism provided by the interaction of infill walls and surrounding frame members, in which the latter remarkably enhances the initial structural stiffness and peak resistance. For the multi-story infilled frame with opening in which the geometric and mechanical properties are identical in each story, the load transfer mechanism is basically independent of the number of stories, whereas for the frame with full-height infill walls, the composite effect of multi-story walls is evident, increasing the peak structural resistance. Therefore, if each full-height infill wall is simplified into equivalent strut models in structural analysis, the results are underpredicted but on the safe side.
Despite the increasing interest in progressive collapse-resistant design and analysis of reinforced concrete buildings that was triggered by accidental and man-made extreme events occurred over the last couple of decades, only few studies, especially numerical ones, have been carried out so far on the role of masonry infill walls. Just like in the case of first earthquake engineering applications, infills are usually considered as non-structural or architectural elements and, hence, their resistance is commonly ignored, given also that current design guidelines do not provide specific indications concerning this point. Although such an assumption leads to an ease in both design and assessment of structures, it may also give rise to misleading and overly conservative results, as the presence of masonry infills may result in extra vertical resistance. Thus, this paper presents the outcomes of a large number of progressive collapse simulations aimed at quantifying the effects of infill walls on the vertical load-carrying capacity of reinforced concrete frames for different levels of damage, thus allowing evaluation of the interaction between these structural elements and the surrounding frame for different regimes/stages of the response. To this end, a macro-model concept was first developed and its effectiveness was then evaluated by comparing numerical results to experimental data from a past test on a one-third scaled planar structure featuring full-height infill walls. After validation, the proposed model was used to predict behavioural changes in the response of infilled reinforced concrete structures as a consequence of parametric variations in the geometry of the selected prototypes. Counterpart bare frames were also analysed in order to present a twofold comparison, in terms of resistance and dissipated energy. Finally, the manuscript describes the results of a further set of analyses, in which uncertainties in the mechanical properties of the masonry infills were modelled and propagated through fibre modelling and pushdown analysis techniques.
Progressive collapse is defined as the spread of an initial damage from one member to another, leading to extensive partial or total collapse of the structure. In this research, the potential of progressive collapse due to a sudden removal of vertical load-bearing elements in reinforced concrete buildings structures with different floor plans such as geometrical regular and irregular floor plans as well as floor plans with and without torsional irregularity were assessed. The buildings were designed according to ACI 318-14 provisions and Iranian seismic code. The progressive collapse potential of the structures was assessed following of a sudden column or shear wall removal in different locations in their first floor using nonlinear dynamic analysis (NDA). Displacement sensitivity and column sensitivity indexes were utilized to compare different cases of load-bearing element removal in each model. Results indicated that in all geometrical regular floor plan, floor plan with reentrant corner and floor plan with torsional irregularity, the most critical case of column removal was removing columns located in outer corners of the plan. In addition, removing external columns was more critical than internal columns. In buildings with shear walls, removing shear walls led to much more critical scenarios than removing columns. Furthermore, results revealed that buildings with torsional irregularity floor plan, designed according to Iranian seismic code, had a lower potential of progressive collapse rather than those buildings with no irregularity.
Structural safety for extreme loads that may cause local damage to single primary components or even the progressive collapse of the structure has been probabilistically assessed in a few studies, hence neglecting uncertainties in loads and system capacity. As such, this paper moves from a deterministic to a probabilistic framework, proposing new progressive collapse fragility models based on pushdown analysis of low-rise, reinforced concrete framed bare structures. Two building classes representative of structures designed for either gravity loads or earthquake resistance in accordance with current European codes were investigated. Monte Carlo simulation was used to generate random realizations of 2D and 3D structural models. Fiber-based finite element models were developed within an open source platform. The primary output consisted of fragility functions for each damage state of interest, given the loss of corner column at the ground floor. The fragility models were compared to those derived through incremental dynamic analysis (IDA) to assess the inaccuracy of progressive collapse fragility functions derived through pushdown analysis. Load capacity predictions provided by those analysis methods were used to develop regression models for a quick estimation of dynamic amplification factor at a given dis-placement/drift level. The analysis results show a significant influence of both seismic design and secondary beams on robustness of the case-study building classes.
In the last decade, a great care is exercised in progressive collapse analysis of structures to avoid the catastrophic consequences of such a system-level problem. The majority of the previous research works dealt with the quantification of resisting mechanisms such as the compressive arching action using two-dimensional frameworks. The three-dimensional (3D) studies are also limited to considering the initial damage as instantaneous removal of one or simultaneous removal of multiple supporting elements. This paper studies the 3D nonlinear dynamic response of reinforced concrete structures subjected to sequential column removal scenarios. A sequential nonlinear time-history analysis algorithm alongside with a macro modeling approach is utilized to predict the dynamic redistribution of the gravity loads. The efficiency of such a numerical framework is verified through comparison of computational results with the available experimental data from a past 3D half-scale test. Good agreement is observed for the global and for the local response quantities. Furthermore, a practical strengthening technique is applied into the computational model of the structural system for artificially activating the catenary mechanism. Analysis results show that strengthening of peripheral beams with externally bonded steel plates significantly increases the rotational ductility at beam-sections and in turn, enables the damaged structure to accommodate larger deformations. Finally, the influence of the removal sequence on the 3D force redistribution mechanism is investigated. Permanent plastic deformations and maximum sectional forces of a sequential removal scenario are found to be larger on average compared with those obtained from an at-once removal scenario. It is demonstrated that the time-lag between the column removals considerably affects the 3D redistribution of gravity loads, and shall not be neglected in case of considering an extreme initial damage.
Floor systems composed of beams and slabs are critical structural elements of frame structures to resist progressive collapse. Previous experimental studies have focused mainly on beam–column or continuous-beam substructures and have ignored the influence of the slab. To study the progressive collapse-resisting mechanisms of reinforced concrete (RC) floor systems, seven 1/3-scaled one-way substructure specimens, including five beam–slab specimens and two continuous-beam specimens without slabs, were tested under a middle-column-removal scenario. The effects of various structural parameters, including sectional dimensions (beam height, slab width, and slab thickness) and seismic reinforcement, on the progressive collapse resistance were studied by analyzing material strains and load–displacement curves. Under small deformations, the progressive collapse resistance was largely affected by the beam height, slab width and seismic reinforcement in the beams. However, the effect of the slab width, upon exceeding the effective flange width, became insignificant. Note that increasing the slab thickness simultaneously increased the amount of slab reinforcement according to the minimum requirement of reinforcement ratio for slabs, such an increase will in turn enhanced the progressive collapse resistance. In addition, the existence of the slab led to an over-reinforced damage in the compressive zones of the beam ends, which accelerated the bending failure and the presence of the catenary action of the specimens. Under large deformations, the progressive collapse resistance was mainly influenced by the reinforcement area of the entire beam–slab section. The total reinforcement area of a beam–slab substructure designed to meet a higher seismic requirement was not significantly increased, and consequently, the progressive collapse resistance of the substructure under the catenary mechanism was not notably improved. This finding stands in stark contrast to those of previous tests of beam–column specimens without slabs.
This article presents a nonlinear static pushdown analysis to evaluate the progressive collapse-resisting capacity curves of typical reinforced concrete frames under different deformations. Unlike the previous studies in which only a few typical columns, such as a column on the bottom storey, are removed, this study examines the column removal scenarios for various typical locations from different stories. The primary findings are as follows: (1) the Vierendeel action causes different internal forces in the beams of different stories, which reduces the progressive collapse resistance under the beam mechanism and delays the development of the catenary mechanism. This may result in the beams failing successively from one floor to another in a frame system, which differs from the theoretical assumption that the beams are damaged simultaneously on different floors; (2) seismic designs significantly improve the progressive collapse resistance under the beam mechanism, especially for lower stories. However such an improvement is less significant for the catenary mechanism and little improvement is found for the top regions of the frame structures. Furthermore, a nonlinear dynamic analysis is conducted to validate the predicted resistances of the reinforced concrete frames in satisfying the requirement of collapse prevention. The design parameters as specified in the existing codes are also discussed.
Results of recent research on the dynamic response, failure mechanism, and changes in the load-transfer paths of a half-scale three-story, three-bay, and three-span reinforced concrete frame subjected to a series of sudden column removals are presented. Three phases of testing were carried out, including the removal of a corner column and a column adjacent to the corner column along the short span direction, two middle exterior columns along the long span direction, and one interior column. The column removal was enabled by using a gas cannon. The dynamic response at critical locations after the imposed failure of the respective columns was observed. The removal of the corner column followed by the adjacent column resulted in only an essentially elastic response of the structure. The removal of an interior column resulted in only small deflections. The removal of the two first-story exterior columns resulted in significant vertical deflections of the middle exterior columns and significant yielding at adjacent beams that framed into the two middle exterior columns. The vertical deflection of these two columns progressed for approximately 14 minutes, at which point the exterior frame collapsed on to preset steel shoring columns. The shift from moment-resisting mechanism to catenary mechanism was identified and the response and failure of the building are discussed using simplified analyses.
One approach to evaluate progressive collapse of structures is to study the effects of instantaneous removal of a load-bearing element such as a column. In this paper using experimental and analytical results, potential progressive collapse of an actual 10-story reinforced concrete (RC) structure following the explosion of an exterior column is evaluated. Development of Vierendeel action is identified as the dominant mechanism in redistribution of loads in this structure. The concrete modulus of rupture is identified as an important parameter in limiting the maximum recorded vertical deformation of the system to only 0.25 in. (6.4 mm). The changes in the directions of bending moments in the vicinity of the removed column and their effects such as potential reinforcing bar pullout (bond failure) are studied. Potential failure modes and their consequences are studied. Some shortcomings of integrity requirements in current codes are pointed out and effects of beam reinforcement detail on the development of catenary action are discussed.
Computational simulations for analyzing progressive collapse resistance of structures following initial damage require specific attention to structural modeling of floor systems. In collapse analysis of RC structures, it is shown that the degrees of freedom of nonlinear beam, joist, and slab sections must include flexural and axial deformations. It is also shown that ignoring torsional cracking of beams can lead to a significant overestimation of the progressive collapse resistance of structures. Evaluating the response of a seven-story RC structure following 15 simulated single column removal scenarios, it is shown that a top floor column removal is more likely to cause structural collapse than failure on a lower floor. This is in part due to the lack of Vierendeel frame action after a top floor column removal. For the simulated scenarios in which the structure resists progressive collapse without experiencing large vertical displacements, the resistance is primarily provided by Vierendeel frame action and axial compressive force-moment interaction of beams. The importance of the floor system in-plane action in axial-flexural response of beams is discussed. The effect of accounting for the elevation difference between the centerlines of floor slabs and beam elements within the building model is studied.
The main goal of this research is to better understand progressive collapse mechanisms of buildings, and to evaluate the current modeling and analysis techniques and design methodologies. Field experiments and numerical simulations were performed to investigate the progressive collapse potential of several reinforced concrete and steel frame buildings. Up to four first-story columns were physically removed from the buildings to understand the subsequent load redistribution within each building. Experimental data from the field tests were used to compare and verify the computational models and analysis results. Due to the scarcity of data from full-scale tests, the experimental data of this research is a valuable addition to the state of knowledge on progressive collapse of buildings. The design guidelines typically recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This research investigates the effectiveness of such commonly used progressive collapse evaluation and design methodologies through numerical simulation and experimental data.
Explosions almost instantaneously damage the structures. The direct action of the high intensity blast on the exposed surfaces of the building may causes damage to the primary structural components like columns and structural walls. Damage can be in form of loss of non-structural element, damage to structural components, and collapse of structural element leading to progressive failure of part or whole building. The failure of a member in the primary load resisting system leads to redistribution of forces to the adjoining members and if redistributed load exceeds member capacity it fails. This process continues in the structure and eventually the building collapses. This phenomenon is referred as progressive collapse of the structure. When a multi storey building is subjected to sudden column failure, the resulting structural response is dynamic, typically characterized by significant geometric and material nonlinearity. Analysis methods used to evaluate the potential of progressive collapse varies widely; ranging from the simple two dimensional linear elastic static procedures to complex three dimensional nonlinear dynamic analyses. In the present study the demand capacity ratios of reinforced concrete four storey and ten storey frame structure are evaluated as per GSA guidelines. The linear static and nonlinear static analyses are carried out using software SAP2000. For progressive collapse analysis, a nonlinear static analysis method employs a stepwise increment of amplified vertical loads which can be referred as vertical pushover analysis. The demand capacity ratios found using linear static analysis at critical locations are compared with the hinge formation obtained from nonlinear static analysis. Comparison of linear static and nonlinear static analysis reveals that hinge formation starts from the location having maximum demand capacity ratio calculated from static analysis.
In light of current world developments, engineers are increasingly being required to consider progressive collapse mitigation as a basic design criterion. Progressive collapse requirements, however, must typically be incorporated into a structure without substantial increases in the cost of the structural system. One method of achieving this goal efficiently is to utilize a multi hazard approach to structural system selection. This paper illustrates how progressive collapse criteria can be economically incorporated into typical structural systems. Although three very different examples are presented, the overall design approach is basically the same. Structural Steel Office Building – The use of some types of moment frames to resist lateral wind and seismic loads can also provide the additional ductility and redundancy required for progressive collapse resistance. Reinforced Concrete Office Building – Analysis of an example existing building indicated that seismically designed reinforced concrete moment frames have an inherent capability of providing progressive collapse resistance. Reinforced Concrete Apartment Building – One cost effective construction method for apartment building construction is the tunnel-form concept. Analysis methods indicate that with minor modifications these structures can be designed to withstand the loss of a supporting wall without experiencing progressive collapse.
A stress‐strain model is developed for concrete subjected to uniaxial compressive loading and confined by transverse reinforcement. The concrete section may contain any general type of confining steel: either spiral or circular hoops; or rectangular hoops with or without supplementary cross ties. These cross ties can have either equal or unequal confining stresses along each of the transverse axes. A single equation is used for the stress‐strain equation. The model allows for cyclic loading and includes the effect of strain rate. The influence of various types of confinement is taken into account by defining an effective lateral confining stress, which is dependent on the configuration of the transverse and longitudinal reinforcement. An energy balance approach is used to predict the longitudinal compressive strain in the concrete corresponding to first fracture of the transverse reinforcement by equating the strain energy capacity of the transverse reinforcement to the strain energy stored in the concrete as a result of the confinement.
This paper presents a plain strain analytical model, based on the elasticity theory, to determine the confining pressures of transverse reinforcements on the concrete core of a reinforced concrete member. The analytical evaluation of the confining pressures was first carried out on reinforced sections with square and circular stirrups, and subsequently on reinforcement configurations of greater complexity with square and rectangular stirrups and supplementary cross ties. Finally, the model has been used to evaluate the confining pressures applied by external wrapping in any material [fiber-reinforced polymer (FRP), S-glass, steel, etc.] and to design better combinations of techniques and confinement materials. In order to obtain the stress–strain curves due to passive confinement, an analogy between square and circular sections has been introduced. In this way, any active confinement model derived by triaxial tests on cylindrical specimens can be used. The model has been validated by comparing its predictions with results from existing models and experimental tests.