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Experimental investigations on ultra-lightweight-concrete encased cold-formed steel structures
Abstract
In the field of structural engineering the design of cost efficient structures is highly important. This led to the development of cold-formed steel structures (CFS). An advanced CFS structure is introduced in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. This material has beneficial insulating and fire protection properties, which makes it a reasonable choice for residential buildings. An experimental programme was performed, to gain information on the flexural and axial behaviour of PAC-encased CFS elements and panels. Both unbraced and braced members were tested to gain information on increment of load-bearing capacity. Several different element sizes were used to be able to investigate the different stability failure modes (i.e. local, distortional and global). Results showed that PAC was able to restrain the global and distortional buckling modes of steel elements, thus providing "full bracing" in most practical cases. These results are introduced in two papers (Part I and II), detailing the failure modes, load increments and the effect of composite action. In this paper - Part II - the background and the results of compression tests are presented, and the bending experiments are detailed in Part I [1].
... Extensive tests were conducted on CFS flexural, compression elements and shear panels. The experiments revealed that PAC significantly impacts CFS's stability, improving its load-bearing capacity [2], [21], [22], [23]. The complexity of these components made their finite element (FE) representation more problematic and time-consuming. ...
... The performance of this modelling technique will be compared against 3-D solid FE model (SMOD) for the case of elastic plate buckling and for ultimate load bearing capacity using GMNIA analysis. As a synthesis of results contained by this paper and [26] the ability of ESM to predict full cross-section resistance of compression elements will be discussed, too, using experimental data reported in [21], [22]. ...
... To examine the validity and limitations of the ESM method, the parameters detailed in Table 1 were used in this study. The ultra-lightweight concrete modulus range is based on the material experiments reported in [21]. Mesh size is the steel plate and infill mesh size in the case of SMOD and the unsupported area between adjacent springs in ESM. ...
An efficient finite element approach was recently developed to analyse encased cold-formed steel (CFS) structures. This new technique replaced encasing material with unidirectional springs, analogous to the Winkler foundation concept, to shorten the analysis time while ensuring accuracy and reliability in predicting the structural behaviour of encased CFS components. In this paper, the validity, and limitations of the simplified spring model to represent outstanding plates were assessed. The investigation demonstrated that the simplified spring model could effectively predict the ultimate load for a wide range of ultra-lightweight concrete moduli (50-250 MPa) with an acceptable error. The analysis indicated that plate elements initially in cross-section class 4 without encasing material become at least class 3, or better as a consequence of encasing. Previously reported experiments were used to evaluate the performance of the ESM. The analysis demonstrated that the ESM can accurately predict the local failure ultimate load of encased CFS sections with an acceptable error percent and significantly less computational effort than a 3D solid model.
... As a filling material, PAC can provide heat, moisture insulation, and fire protection owing to its polystyrene granules and admixtures composition instead of gravel or sand [33]. In [1], [34], [35], [36] , PAC was introduced as a promising and efficient construction material that can be used beneficially in residential buildings. The experimental results indicated that PAC-bracing markedly restrained global buckling failure, improving the stability of centrally loaded CFS columns and flexural strength of tested specimens, resulting in load-bearing capacity enhancements of 10-110 % and 30-190 %, respectively. ...
... The aim of the current paper is to expand the available experimental results already published in [1], [2], [34], [35], [36], [38] with a new loading type, i.e. eccentric compression. The behaviour, load bearing capacity and effect of different cross-sections will be discussed herein which are necessary to make further developments to the proposed design method in [2]. ...
... Hence, due to cement segregation phenomenon, high scatter in PAC properties can be achieved even within one type of mixture. For practical use, the material characteristics can be assessed by the bulk density of the mixture, which is directly correlated with the amount of cement present [34], [35]. ...
Nowadays, cold-formed steel (CFS) has become widely used in the field of lightweight structures. In 2016, the Budapest University of Technology and Economics initiated a research on a unique structural system using CFS and utilized ultra-lightweight concrete as an encasing material. This material serves as a continuous bracing that improves CFS element resistance, stability behaviour, and performance, while also providing heat insulation capabilities, thus helping achieving sustainability goals. This paper is considered a continuation of previous research conducted by the authors. An experimental investigation was carried out on encased CFS columns subjected to eccentric loading. A total of fourteen stub-columns, with two distinct thicknesses, were subjected to various loading conditions for testing. The test results showed that local failure controlled the behaviour of all the tested elements. The reduction in capacity resulting from eccentricity with respect to centric resistance varied between 20% and 52%, depending on the applied load position and the core thickness of the tested steel elements. Moreover, the test outcomes were compared to the Eurocode analytical solution of pure steel elements. The overall load increment ranged from 46% to 18%, with a more noticeable bracing impact observed in the case of slender elements. Material test also supplement the results.
... Their findings demonstrated the importance of the infill material, demonstrating how lightweight foamed concrete enhances structural response, leading to an innovative structural system with a sufficient load-carrying capacity that may be utilized for low-rise structures. Likewise, a novel investigation path was carried out by Hegyi et al. [5,6], who intended to improve the stability of CFS members utilizing polystyrene aggregate concrete (PAC) as encasing material. Intensive experiments were conducted on CFS flexural [2], compression [5] elements and shear panels [1,6]. ...
... Likewise, a novel investigation path was carried out by Hegyi et al. [5,6], who intended to improve the stability of CFS members utilizing polystyrene aggregate concrete (PAC) as encasing material. Intensive experiments were conducted on CFS flexural [2], compression [5] elements and shear panels [1,6]. The braced CFS experiments demonstrated that PAC significantly impacts the stability of CFS, hence increasing its load-bearing capacity. ...
... A modelling framework for structural members was developed where the equivalent spring stiffness was defined based on the critical buckling stress using the approximated equation in [14]. The modelling framework was calibrated to experimental data of compressed C-section members found in [5]. The modelling framework showed acceptable results, but it also has its limitations. ...
Using concrete for filling and bracing is one of the most crucial ways to improve cold-formed steel (CFS) elements' stability behavior and performance. An example is the novel building system made up by CFS encased in ultra-lightweight concrete. The numerical analysis of such structural members using solid finite elements is time-consuming, thus the need for an easy-to-use modelling technique has arisen. As a result, a simple time-efficient equivalent spring model (ESM) has been introduced as a viable method for properly analyzing complex structural behavior in numerous cases, replacing the concrete solid with one-directional springs applying the Winkler foundation. This study aims to examine the validity and limitations of the ESM by comparing it to 3D solid model (SMOD) results for internal plate elements. The analysis results indicate that the ESM could provide accurate results in the b/t range of 100 or less for a wide range of PAC modulus (50–250 MPa) with an error of less than 5%; hence, using spring in modelling PAC within these limits is deemed acceptable. Nevertheless, for larger b/t values up to 175, doubled the calculated spring stiffness is highly recommended. In addition, the results reveal that the applicability of ESM is limited for b/t above 175; the model fails to predict the ultimate failure load, and the failure mode. Finally, this study ends by recommending one equation for calculating equivalent foundation spring stiffness for internal components that ensure optimal performance of the ESM analysis.
... Nowadays, many novel research projects have been conducted to investigate new con gurations of thin-walled steel structures. For example, an experimental project was conducted at the Budapest University of Technology and Economics in Hungary to test CFS elements encased in lightweight concrete [1]. is experimental program was used in this paper to validate the numerical model. ...
... e results showed that they showed better performance compared to normal-strength concrete (NSC) and high-strength concrete (HSC) lled columns. Likewise, the exural [6] and axial [1] behaviors of polystyrene aggregate concrete (PAC) braced CFS specimens were tested. In this case, only the local buckling mode was observed, and the capacity was enhanced. ...
... Consequently, this paper aims to present a simplified numerical model of the experimental tests that were conducted by Hegyi and Dunai [1], where shell and spring elements were used instead of shell and volume elements. ...
The utilization of cold-formed steel (CFS) elements has become more popular recently, due to their cost efficiency and feasibility in constructional work. Nevertheless, since such elements are subjected to a variety of complex stability issues, numerous approaches of strengthening have been examined. Namely, CFS members were braced by using lightweight concrete through a previous experimental program. A simplified finite element model was performed; consistently with the previous experimental work, to estimate the ultimate load of encased CFS members subjected to compression. The main aim of this research was to overcome the difficulties of modeling the concrete block by substituting the volume element with springs. In addition, a practical equation was proposed to predict the stiffness of springs and an imperfection amplitude was set to obtain the design capacity of braced CFS compressed elements.
... However, the observed failure modes for the three types were the same. Moreover, Hegyi and Dunai made use of lightweight concrete as a bracing, where they performed an experimental program to investigate the flexural [9] and axial [1] behavior of polystyrene aggregate concrete (PAC) braced CFS elements and panels. The effect of PAC has led to increment of load-bearing capacity and to restrain the global and distortional buckling modes of steel elements. ...
... The results revealed that the load-bearing capacity was increased by 10-110%. Additionally, seven specimens of fullscale panel tests were conducted, where the main failure mode was related to the load transition zone [1]. Another kind of strengthening is the use of CFRP, whereas Shen et al. [10] studied experimentally and numerically the behavior of partially CFRP-wrapped thinwalled circular NCFST stub columns under axial compression. ...
... This paper presents a numerical simulation of the experimental results reported by Hegyi and Dunai [1]. The aim of the modelling was to simulate the behavior of PAC encased CFS columns. ...
The use of thin‐walled structures has been increasingly spread in the last few decades due to their big advantages in both structural design and construction methods. Therefore, the recent researches have discussed a wide range of thin‐walled structures applications. However, the resistance of such structures will be decreased by buckling effect; hence, different ways of strengthening methods have been investigated. One of this method is the use of lightweight concrete as a filling of thin‐walled members. Previous experimental research at the Department of Structural Engineering at Budapest University of Technology and Economics, was carried out to investigate the axial behavior of polystyrene aggregate concrete (PAC) braced CFS elements [1]. The effect of PAC has led to increase the load‐bearing capacity and to restrain the global and distortional buckling modes of steel elements. The results revealed that the ultimate load was increased by 37‐94%. A simplified nonlinear finite element model was developed in ANSYS software to be able to predict the peak resistance of PAC filled thin‐walled members. GMNI analyses were carried out to validate the numerical model by the experimental tests. The concrete was modelled by using springs with adequate stiffness, where a parametric study was conducted to determine the proper imperfection amplitudes of different element lengths. The numerical model showed good agreement with test results.
... Foam concrete acts as a filling material due to its effective thermal insulation and ability to withstand fires. Meanwhile, related studies have shown that, due to the interaction between C-shaped steel and foam concrete, foam concrete is considered effective in restraining the early local buckling of C-shaped steel under compression [26,27]. Cement mortar serves as an interior surface The following is how the composite wallboard is made: (1) Erect the side formwork on the formwork platform according to the size of the wallboard, lay the decorative materials on the formwork counter, and spray polymer mortar with a thickness of 3-5 mm; ...
... Foam concrete acts as a filling material due to its effective thermal insulation and ability to withstand fires. Meanwhile, related studies have shown that, due to the interaction between C-shaped steel and foam concrete, foam concrete is considered effective in restraining the early local buckling of C-shaped steel under compression [26,27]. Cement mortar serves as an interior surface layer to facilitate interior decoration. ...
In order to expand the applications of cold-formed thin-walled steel structures, this study proposes a new type of composite wallboard composed of cold-formed thin-walled C-shaped steel and multi-layer concrete, in which C-shaped steel serves as the skeleton, foam concrete acts as the thermal insulation material, and fine aggregate concrete and cement mortar play the part of envelopes. The composite wallboard can be made in a factory assembly line, meeting the requirements of the building (civil and structural) industry. Two steel-frame composite wallboard shear walls were subjected to reciprocating loading, with the connection mode as the design parameter, to investigate the seismic performance of the structure. The failure mode, hysteresis curve, skeleton curve, strength degradation, stiffness degradation, ductility, and energy dissipation capacity of the specimens were analyzed. On this basis, the finite element (FE) model of the steel-frame composite wallboard was established, and the model’s accuracy was verified by comparing the bearing capacity and the skeleton curve. Results show that the structure shows shear failure characteristics, and the cement mortar layer and the fine aggregate concrete layer are separated from the C-shaped steel after being crushed. The infilled foam concrete is also crushed, and the welding seams between the extended C-shaped steel and steel frame of the WP-1 specimen are damaged. The hysteresis curves of the two specimens have a clear pinch, but the area enclosed by the hysteresis loop is large, and the energy dissipation capacity is also present. The yield load and ultimate load of the WP-2 specimen are higher than those of the WP-1 specimen, indicating that the higher the connection strength between the composite wallboard and the steel frame, the greater the ultimate carrying capacity of the specimen. The established FE model can accurately estimate the seismic performance of steel-frame composite wallboard shear walls.
... Apart from these abovementioned works, different types of filling materials are adopted in CFS shear walls to promote the performance. The material using in the CFS shear wall mainly include lightweight mortar [13], lightweight concrete [14], lightweight foamed concrete [15], high-strength lightweight foamed concrete [16], and lightweight flue gas desulfurization gypsum [17]. Nevertheless, available literatures concerning this type of LPM-filled CFS shear wall and the effect of LPM on the CFS shear wall can rarely be found. ...
... The results of the test lateral stiffness and those predicted based on the simplified model are compared in Table 5. The specimens from Ref. [14] and Ref. [15] are also adopted to verified the reliability of Eq. (12) ...
The light polymer material (LPM), prepared with suitable mix proportion and physical method, is a type of low-carbon and environmental-friendly material. Recently, the LPM is developed as structural material for cold-formed steel (CFS) structures to cover the shortages of traditional CFS shear wall. In this paper, material properties of gypsum-based and cement-based LPM including compressive strength, elastic modulus and thermal property were explored by tests. Experimental results demonstrate that LPM exhibits excellent thermal insulation, and the thermal insulation and compressive strength of LPM satisfy the demand of bearing capacity and thermal insulation property of shear walls. To explore the effect of LPM on seismic response and failure modes of CFS shear walls, three specimens are manufactured and tested under cyclic loading. The existence of LPM in CFS shear wall would restrain the failure of wall studs to some extent. Due to the restriction effect of LPM on wall studs and self-drilling screws and the bond-slip performance between LPM and studs, the shear walls exhibit better seismic behavior than traditional CFS shear walls. At last, a modified equivalent bracing model is employed to predict the lateral stiffness of LPM-filled CFS shear walls considering the effect of filling materials, rib lath, and sheathing. The lateral stiffness obtained by the proposed method is compared to the experimental results in this paper and other researches, and the proposed model is proved to supply a conservative result which is safe to be adopted in the design and application of the LPM-filled CFS shear wall.
... Incorporating various load-bearing materials into the infill of the wall frame can provide additional stiffening and prevent local buckling of the CFS frame while improving the wall's axial compression capacity, seismic performance, and ductility. Hegyi and Dunai [8,9] successfully used polystyrene aggregate concrete as a bracing material to restrain the global and ductility. It is expected that this study will provide valuable insights into the design and optimisation of CFS composite structures for various applications in the construction industry. ...
This study presents an innovative design for a cold-formed steel polyurethane (CFS-PU) composite wall panel, combining a cold-formed steel frame, a polyurethane foam infill, and a gypsum fibreboard sheathing. The foam filling process, in which the foam is injected under pressure, ensures uniform distribution, bonding, and interaction of all panel components. The aim of the study is to evaluate the behaviour of the CFS-PU composite panels and the influence of the PU foam and sheathing on the performance of the CFS frame structure. For this purpose, a comprehensive test programme was conducted with nine full-scale specimens, including four CFS-F specimens without infill and sheathing and five CFS-PU specimens with infill and sheathing on both sides. The study examined various aspects of the specimens, including failure modes, stability, stiffness, load-bearing capacity, and ductility index. By analysing these parameters, valuable insights were gained into the performance characteristics of the composite wall panels. The load-bearing capacity of the CFS-PU test specimens was improved by 2.34 times and the stiffness by 1.47 times compared to the CFS-F test specimens. The positive results highlight the potential of foam and sheathing in improving the axial compression performance of CFS walls.
... As the main load-bearing members in CFS structures, CFS walls are typically composed of wall frames covered with a variety of wall sheathings by means of self-drilling screw connections (AISI, 2007;Mohurd, 2018), providing lateral resistance for the structures. To improve the lateral resistance of the walls, CFS walls infilled with different lightweight materials such as lightweight mortar (Liu et al., 2016;Yu et al., 2015), foamed concrete (Xu et al., 2018a(Xu et al., , 2018b, lightweight concrete (Hegyi and Dunai, 2016;Wang et al., 2020), lightweight flue gas desulfurisation gypsum (Wu et al., 2018) and so on have been tested by many scholars. Test results have shown that infill materials can effectively improve the shear capacity and seismic performance of walls. ...
To improve the seismic behaviour of cold-formed steel (CFS) walls, a novel infilled CFS wall covered with different wall sheathings (gypsum wallboard, oriented strand board and fibre cement board) was assessed. Four full-scale specimens were tested under cyclic lateral loads to investigate the impacts of the wall sheathings on the seismic performance of the CFS wall. The failure process, failure mode, load–displacement curve, strength degradation, stiffness degradation, energy dissipation, deformation and strain variation of the walls were investigated. The failure modes of the walls were found to be failure of the connections between the CFS frame and the sheathing as well as crushing of the infill material. Compared with a specimen without sheathing, the peak load and lateral stiffness of the walls with sheathing were increased by 1.25–1.72 times, indicating that the sheathings played an important role in the lateral resistance of the wall. An analysis model and formulas for predicting wall lateral stiffness were developed. Comparisons between the calculations and experimental data showed that the proposed theoretical method was able to predict the lateral stiffness of the infilled CFS walls accurately.
... In recent years, to further improve the bearing capacity of the wall, researchers have proposed to add infill materials to the CFS walls. The filling materials mainly included lightweight concrete [14][15][16], desulfurization gypsum [17,18], lightweight mortar [19], lightweight foamed concrete (LFC) [20] and so on. The results showed that the filling materials can improve the stability and stiffness of the wall, restrain premature buckling of studs, and increase the axial load-bearing capacity of the structure. ...
To study the effect of filling phosphogypsum (PG) on the axial compression behavior of cold-formed thin-walled steel (CFS) walls, four full-scale test specimens were designed and fabricated, in consideration of the filling regions of PG as well as measures with or without wall sheathings. The fabricated specimens were tested under monotonic vertical loads, and the failure processes and failure modes of specimens were elaborated. Each specimen’s axial load-displacement curve, bearing capacity, strain curve, and energy dissipation capacity were investigated in detail. Furthermore, the internal force distributions of wall components and failure mechanisms were revealed. The test results indicated that the failure characteristics of specimens include the buckling of the steel tubes, cracking of wall sheathings, crushing of PG, and distorting of tracks. Compared with the cavity wall specimen, the axial bearing capacity of the specimen filled with PG in the studs only increased by 37.4%, and the bearing capacity of the specimen filled with PG in and between the studs increased by 115.7%. This indicates that filling PG can effectively improve the axial bearing capacity of CFS walls. The bearing capacity of the specimen without wall sheathings is lower than that of the specimen with wall sheathings, indicating that the wall sheathing has a beneficial effect on the bearing capacity of the specimen. In addition, the internal forces of components during the loading process were analyzed. It found that the steel tube and PG made a great contribution to the bearing capacity of the wall. Specifically, the steel tube played a leading role in the early loading stage, while the PG played a leading role in the later loading stage.
... The number of hybrid or multi-material structural solutions in use will increase significantly, targeting enhanced structural performance [17]. The composite behavior of CFS-concrete members has been investigated in the past, where the CFS profiles have also been considered as a replacement for traditional reinforcement bars, and others assessing the benefits and potential of composite structures combining CFS products and concrete [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Several studies were undertaken to investigate the behavior of shear connectors and composite beams [19,20,22,[27][28][29][30][31], showing high levels of ductility and load-bearing capacity. ...
Concrete-filled composite columns are widely used in the construction industry, exploiting the benefits of combining steel and concrete, providing, for instance, high load-bearing capacities and enhanced fire resistance. These solutions are extensively used in high-rise buildings and/or when high fire resistance performance requirements are imposed. In this exploratory research, a new type of concrete-filled composite column is investigated using fire resistance tests. Promoting the use of cold-formed steel products and developing innovative solutions for low-rise buildings with lower passive fire protection requirements led to the solutions presented in this research. Hence, a set of fire-resistance tests were undertaken on concrete-filled closed built-up cold-formed steel columns, where single cold-formed steel shapes are combined and fastened to create a box-shaped cross-section. The experimental results were then compared with the corresponding bare steel solutions to assess, in detail, the observed enhancements. Additionally, the effect of restraint on thermal elongation was assessed.
... With the deepening of researches, various lightweight materials had been filled inside the CFS framing cavities to improve the performance of CFS walls. Hegyi and Dunai [19,20] studied the ...
Introduction of filling materials, such as lightweight polymer material (LPM), is very beneficial for traditional cold formed steel (CFS) walls. A further improvement of CFS walls via introducing LPM is that it is expected to enhance the sound insulation property and thermal insulation. In order to explore the compressive behaviour and bearing capacity of CFS composite walls sprayed with LPM, five full-scale specimens were tested under axial compression loading. Furthermore, effects of infilled material type and sheathing type on the axial compressive response of this type of CFS composite wall were explored. Failure modes, axial force-displacement relationships, axial load-strain responses, axial bearing capacities and ductility indexes of the test specimens were also studied and estimated. The tests showed that the wall studs, infilled material and wall sheathing together resisted the axial compression. Clear evidences were obtained that the axial bearing capacity and axial compressive stiffness of CFS composite wall sprayed with cement-based LPM were significantly higher than those sprayed with gypsum-based LPM. Wall sheathing can improve the axial compressive behaviour of composite walls. Additionally, a formula for predicting the axial bearing capacity of CFS composite wall sprayed with LPM was put forward and verified by the test data. The experimental and analytical results can promote the design and application of CFS composite walls sprayed with LPM in low- or mid-rise.
... The investigated ultra-lightweight building construction is a composite system of a newly developed Expanded PolyStyrene (EPS) concrete and thin-walled steel loadbearing elements. This structure can be a substitute of steel frame houses [1], since polystyrene concrete has a good thermal insulating capability [2], and it is able to restrain the global and distortional buckling modes of steel elements [3], [4]. However, there was research of load-bearing ultra-lightweight concrete as well, that also performs as thermal insulation [5]. ...
The aim of the paper is to investigate the hygrothermal properties of a newly developed building panel, made of ultra-lightweight concrete, encased cold-formed steel elements. It describes the hygrothermal simulations of the wall and roof panels, and based on results, the heat transfer coefficients and linear thermal transmittances are determined. The hygrothermal behavior of main structural joints (wall corner, wall-roof and wall-ground connections) is also simulated using real indoor and outdoor conditions. For validating the results, a model building was investigated.
This paper presents experimental studies to investigate the compressive and shear behaviors of cold-formed thin-walled steel-foam concrete composite walls. Three compressive walls and three shear walls were tested. The failure mode and load-displacement curve of the specimen were obtained from the compressive experiment. The compressive wall infilled with foam concrete mainly experienced distortion buckling of the end stud and local crushing failure of the concrete. The stud openings had a limited effect on the compressive bearing capacity of the composite wall. The failure mode and load-deformation curve were obtained in shear tests. The ductility index, shear stiffness, yield load, peak load, energy dissipation, and stiffness degradation were analyzed. The shear composite wall filled with foam concrete mainly occurred concrete crushing failure, local or distortional buckling failure of the end stud, and cracking failure of the calcium silicate board. The shear stiffness, shear capacity, ductility, and energy dissipation of the composite wall could be significantly improved after filling with foam concrete.
In order to improve the shear capacity and seismic performance of cold–formed thin–walled steel (CFS) walls, in this research, a novel CFS wall filled with phosphogypsum (PG) was developed. Taking PG filling area and covering the wall with sheathing as design parameters, four full–scale test specimens were designed and constructed. Failure mode and seismic performance indexes of each specimen were investigated by performing cyclic loading tests and the effect of PG filler on CFS wall seismic performance was evaluated. Research results showed that PG filler significantly improved the seismic performance and shear capacity of CFS walls. Importantly, the proposed wall presented a remarkable dual–mechanism of lateral force resistance, which was provided by PG filler and wall sheathings, respectively. In addition, analytical models were developed for the calculation of the shear capacity and lateral stiffness of the proposed walls, which presented high prediction accuracy.
A building system, promising cost‐efficient residential buildings, is under development. The system uses cold‐formed steel as load‐bearing member and encases it in polystyrene aggregate concrete, a special ultra‐lightweight concrete, which plays building construction roles, and provides increment of load‐bearing capacity, too. Previous research was focusing on individual member design for axial and flexural effects. In order to provide 3D rigidity for buildings horizontal effects (wind load, earthquake, imperfections) should also be considered. The load transfer of the investigated structural system is significantly different for horizontal and vertical (gravitational) actions thus the previously derived design method has to be expanded to describe the resistance against horizontal actions. This paper briefly introduces the building system and deals with some of the components necessary for providing 3D rigidity. Shear panel tests were carried out in order to identify the stiffness, failure mode and load‐bearing capacity of panels. Then two types of panel connection were investigated: (i) slab‐to‐wall, and (ii) wall‐to‐wall. Tests aimed to study the failure mode and load‐bearing capacity of joints. Test‐based design values were determined based on measured data.
Purpose – The purpose of this study is to improve the lateral capacity of Cold-Formed Steel (CFS) frame walls filled with lightweight foamed concrete (LFC) and supported with straw boards by introducing structural foamed concrete and/or bracing.
Design/methodology/approach – Finite element models are developed and calibrated based on previous experimental work. Then, these models are extended to conduct a parametric study to quantify the effect of filling CFS walls and structural LFC and the effect of supporting CFS walls with bracing.
Findings – Results of the study conclude that the finite element analysis can be used to simulate and analyze the lateral capacity of CFS walls effectively since the maximum deviation between calibrated and experimental results is 10%. The structural LFC usage in CFS walls improves the lateral capacity considerably by (25–75) % depending on the wall properties. Besides, the application of lateral bracing does not always have a positive
effect on the lateral performance of these walls.
Originality/value – Although CFS walls are preferred due to it is light in weight, low in cost, easy to install and recyclable, low seismic performance, buckling vulnerability, poor thermal insulation and sound insulation properties, low lateral stiffness, and low shear strength limit their use. This study proposes the use of structural foamed concrete and a different bracing method than what is available in the literature. This can overcome the
drawbacks of the CFS walls alone which can permit the usage of such walls in mid-rise buildings and other applications.
In this paper, an innovative high-strength foamed concrete (HFC)-filled cold-formed thin-walled steel (CTS) composite wall sheathed with straw-fiber boards (HFCS composite wall) was proposed. Six full-scale specimens of HFC-filled and unfilled CTS composite walls were tested under compression loading. The influence of HFC strength, stud cross-sectional area, wall thickness and sheathing as main parameters on axial compressive behavior of HFC-filled composite wall were analyzed. Test results indicated that using of HFC changed the failure mode of CTS frame from straw’s shear failure to stud’s local failure, and improved the wall’s axial resistance capacity due to the restrictive effect of HFC on CTS-frame. Moreover, increasing HFC compressive strength further enhanced the bearing capacity of the HFCS composite wall, with little effect on its failure mode. Increasing CTS section area and wall thickness effectively avoided early the stud’s local buckling, thereby improved the wall’s compressive capacity. However, numerical analysis results showed that the most contribution of the wall components to axial compressive capacity of the HFCS composite wall is CTS studs (52.1%), followed by HFC (42.3%) and straw boards (5.6%), whereas straw board has no obvious effect. Finally, a practical formula for predicting the wall’s axial resistance capacity was built by superposition method. The calculated results exhibited better agreement with test and numerical results.
An alternative structure for RC beam is a challenging factor in the field of structural engineering. Various studies had been conducted to introduce a cost-effective light weight structure which can replace RC structure. Studies on Glass Fiber Reinforced Gypsum (GFRG) panel sandwitched with Cold Formed Steel (CFS) is one such recent alternative technique to RC structure. In this paper, a GFRG laminated beam developed and strengthened by encasing Cold Formed Steel (CFS) internally and externally is analyzing using ANSYS 16.1 Software for evaluating flexural behaviour of developed beam. It is expected that this combined arrangement of GFRG panel and CFS will provide a cost-effective, light weight and load bearing structure with substantial strength to replace RC.
High-strength lightweight foamed concrete (HLFC), as a new type of load-bearing structural material, was developed using suitable mix proportion and physical method in this study. Material properties of HLFC with dry density of 500 kg/m³ and 700 kg/m³ were studied by a series of tests. To investigate the effect of HLFC on seismic behavior of cold-formed steel (CFS) shear walls, three shear wall specimens were fabricated and tested under in-plane cycle loading. The effects of HLFC on failure mode, load-bearing capacity, ductility, stiffness degradation and energy dissipation capacity of the walls were analyzed. Test results indicated that HLFC with density grade of A05 and A07 exhibit higher compressive strength and better thermal insulation than conventional foamed concrete. Furthermore, the compressive strength and thermal insulation of HLFC meets the requirements of both the load-bearing capacity and thermal insulation property of shear walls. Moreover, the use of HLFC in CFS shear wall changes failure mode of the walls from local failure to shear failure. Due to compressive strength of HLFC, restriction effect of HLFC on steel frame and bond-slip behavior between HLFC and studs, HLFC-filled CFS shear walls are superior to conventional CFS shear wall in terms of load-bearing capacity, ductility, stiffness and energy dissipation capacity. Finally, based on shear strength of the HLFC-filled CFS shear walls, the existing formula proposed by the standard CNS 383-16 is suitable for predicting the shear strength of HLFC-filled CFS shear walls, and the differences between the experimental and calculated results were within 10%.
To improve the seismic behavior of cold-formed steel (CFS) shear walls, cold-formed steel high-strength lightweight foamed concrete (CSHLFC) shear walls with straw boards are proposed. This study conducted tests of six full-scale shear wall specimens to investigate the failure mode, load-bearing capacity, ductility, stiffness characteristic and energy dissipation capacity. The test parameters included HLFC density grade, stud section area, wall thickness and vertical load. Test results indicated that HLFC has greater effect on seismic performance and failure mode of the shear walls. The failure modes were cracking and crushing of HLFC, cracking of straw boards, local buckling of studs, and relative slippage between HLFC and studs, which made the wall exhibit good ductility and energy dissipation capacity. Compressive bearing capacity of HLFC and restrictive effect of HLFC on steel frame increased the shear strength and stiffness. The most effective way of improving seismic performance was to increase wall thickness, followed by increasing HLFC density grade and stud section area, but increasing vertical load had an adverse effect on seismic performance. Based on experimental results and mechanism analysis of shear walls, a simplified design formula for predicting the shear strength was proposed base on strut-and-tie model. The calculated results obtained by the proposed formula showed better agreement with the experiment results compared with the results from ACI 318-14, EC8 and CNS 383-16 standards.
A new direction of development in the field of light-gauge building systems is when the load bearing elements made of cold-formed steel (CFS) sections are encased in an ultra-lightweight material. This material, apart from heat insulation and fire protection effects, can provide bracing effect to the CFS elements, too, therefore can increase the resistance against stability failures. Such lightweight material is the polystyrene aggregate concrete (PAC). Based on previous experimental results this paper develops design method for calculating local, distortional and global resistance of PAC-encased CFS C-sections. The proposed design method is based on the specifications of Eurocode, therefore applies the effective width method for calculating local buckling. The proposed procedure considers the effect of continuous bracing of PAC by replacing it with an elastic half-space, similar to sandwich beam theory. Close form equations are derived to be able to calculate the effective width of plate elements by hand calculation. Distortional buckling is treated as buckling of an equivalent beam resting on elastic foundation, considering the additional stiffness provided by the infill material. The global flexural buckling failure modes of columns are dealt with separately using different mechanical models. Each calculation procedure was compared to existing experimental results in order to evaluate them.
In the field of structural engineering the design of cost efficient structures is highly important. This led to the development of cold-formed steel structures (CFS). An advanced CFS structure is introduced in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. This material has beneficial insulating and fire protection properties, which makes it a reasonable choice for residential buildings. An experimental program was performed, to gain information on the flexural and axial behaviour of PAC-braced CFS elements and panels. Both unbraced and braced members were tested to gain information on increment of load-bearing capacity. Several different element sizes were used to be able to investigate the different stability failure modes (i.e. local, distortional and global). Results showed that PAC was able to restrain the global and distortional buckling modes of steel elements, thus providing "full bracing" in most practical cases. These results are introduced in two papers (Part I and II), detailing the failure modes, load increments and the effect of composite action. In this paper - Part I - the background and the results of bending tests are presented, and the experiments on the compression elements are detailed in Part II [1].
Cold-formed steel wall studs generally are I, Z, or channel shaped with or without stiffening lips and with webs perpendicular to the plane of the wall. Because of their configuration and dimensions, these sections are quite unstable by themselves. However, the stability and, thus, the load-carrying capacity of such studs are increased substantially once they are connected to the wall board material. In this paper the general behavior is formulated and a design procedure is presented. The analytical results are verified on the basis of an experimental investigation.
In the field of structural engineering the design of cost efficient structures is highly important. This led to the development of cold-formed steel structures (CFS). An advanced CFS structure is introduced in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. This material has beneficial insulating and fire protection properties, which makes it a reasonable choice for residential buildings. An experimental program was performed, to gain information on the flexural and axial behaviour of PAC-braced CFS elements and panels. Both unbraced and braced members were tested to gain information on increment of load-bearing capacity. Several different element sizes were used to be able to investigate the different stability failure modes (i.e. local, distortional and global). Results showed that PAC was able to restrain the global and distortional buckling modes of steel elements, thus providing "full bracing" in most practical cases. These results are introduced in two papers (Part I and II), detailing the failure modes, load increments and the effect of composite action. In this paper - Part I - the background and the results of bending tests are presented, and the experiments on the compression elements are detailed in Part II [1].
This research aims to identify and characterize the behavior of dissimilarly sheathed cold-formed steel (CFS) lipped channels (studs) under axial load and bending. These experiments are part of a larger effort to improve design methods and general understanding of CFS columns and their components, utilizing standard construction methods and sheathing configurations: Oriented Strand Board (OSB) and gypsum board. Previous work on sheathed studs and full-scale walls (Vieira, 2011) under axial compression alone demonstrated that sheathing on both sides of the member triggered a local buckling limit state and further restricted global and distortional modes. This was found to be true even for dissimilarly sheathed members, excepting walls and studs sheathed only on one side. In the tests conducted herein single CFS studs, sheathed with OSB or gypsum, or left bare (and any combination thereof on the two sides of the stud) are tested in axial compression and bending. Axial compression was applied to a pre-determined percentage of axial peak capacity (varying from 10% to 80% of the axial capacity of the stud) and then a horizontal load located at specimen mid-height was applied until failure. This configuration results in axial load, bending, and a direct torsion on the CFS stud. To stabilize the stud, tracks at the stud ends were clamped to the top and bottom of the testing rig to avoid liftoff during application of the horizontal load and to better simulate the response of full-walls, with multiple studs and wider sheathing. The immediate goal of the tests is to define the strength of similar and dissimilarly sheathed studs under combined loads. Sheathing type as well as configuration with respect to the loaded face was found to significantly effect the specimen response. Results are compared to nominal section strength. The combination experimental and analytical results will be utilized in full-scale CFS building experiments, modeling, and recommended changes to the AISI specification.
This research is focused on the experimental study of the structural strength of cold-formed steel wall frames with sheathing under monotonic shear loading. Two aspect ratios, 1.0 and 2.0 were utilized in the design of wall specimens. Three different kinds of sheathing material, gypsum board, calcium silicate board, and oriented-strand board, with two different thicknesses (9 and 12mm) were adopted in the test specimens. The ultimate strength, stiffness, energy absorption, and ductility ratio were studied for each test specimen. In final, the ductility ratios of the cold-formed steel wall frames similar to the wall configuration conducted in this study are proposed.
The stability and strength of cold-formed steel lipped C-section columns (studs) with sheathing attached to the flanges is the subject of this paper. Stud configurations both with and without sheathing, either oriented strand board or gypsum board, are tested for failure in compression. A total of twenty-six tests covering short, intermediate and long specimens, varied sheathing configurations, and varied end boundary conditions are completed. Dimensions and geometric imperfections of the specimens are measured in detail. The measured geometric imperfections are reduced to scalar magnitudes consistent with local, distortional, and global buckling modes. During the testing, mid-height cross-section deformations are recorded using five position transducers. The deformations indicate the impact of the different combinations of sheathing, and of the end boundary conditions, on the strength and stability of the studs. Composite action between the stud and sheathing, and isolating direct loading of the sheathing, are shown to be significant in determining the strength and controlling limit state of the stud. Tested strengths are compared with existing North American (American Iron and Steel Institute) specification methods and potential improvements are explored.Research highlights► Tests on sheathed cold-formed steel studs. ► Influence of sheathing type (e.g., gypsum) and stud length explored. ► Sheathing insures local buckling limit states. ► Dissimilar sheathing (different on the two sides) is effective in the observed tests. ► Observed capacities are greatly in excess of current prediction methods.
Gypsum plasterboard is a common lining material used in cold-formed steel wall frame systems. It is used either with lipped or unlipped (plain) C-section studs in the construction of both the load bearing and non-load bearing walls in residential, industrial and commercial buildings. The design of these wall frames does not utilise the full strengthening effects of the plasterboard in carrying the axial loads. An experimental study has shown that the strength of the studs in compression was increased significantly when they were lined with plasterboard on one or both sides. In order to fully understand the behaviour of both sides lined steel wall frames, a finite element model was developed and validated using experimental results. This was followed by a detailed parametric study using finite element analyses. This paper presents the details of the finite element modelling of both sides lined wall frames and the results. A design method based on appropriate effective length factors was developed within the provisions of Australian/New Zealand Standard for cold-formed steel structures to predict the ultimate loads and failure modes of both sides lined steel wall frames.
Thermal insulation capacity of concretes by expanded polystyrene aggregate, The Fourth International fib Congress, Proceedings
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Lublóy, É., Balázs, L. Gy., Kopecskó, K., Tóth, E., Dunai, L., Hegyi, P., Drávucz, O.:
Thermal insulation capacity of concretes by expanded polystyrene aggregate, The Fourth
International fib Congress, Proceedings, pp. 750-751., Paper No.214., 2014, Mumbai, India
Polystyrene aggregate lightweight concrete
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Balázs, Gy., Kovács, K., Papp, A.: Polystyrene aggregate lightweight concrete, Scientific
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Special concretes III
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Balázs, Gy.: Special concretes III., Akadémiai Publisher, 2010, Budapest, Hungary (in
Hungarian)
Full-scale testing of sheathed cold-formed steel wall stud systems in axial compression
- L C M Vieira
- B W Schafer
Vieira Jr., L.C.M., Schafer, B.W.: Full-scale testing of sheathed cold-formed steel wall stud
systems in axial compression, Proceedings of the Structural Stability Research Council -Annual Stability Conference, Orlando, FL. pp. 533-552, 2010
Experiments on sheathed cold-formed steel studs in compression
- L C M Vieira
- Y Shifferaw
- B W Schafer
Vieira Jr., L.C.M., Shifferaw, Y., Schafer, B.W.: Experiments on sheathed cold-formed steel
studs in compression, Journal of Constructional Steel Research, Vol.67/10, pp. 1554-1566,
2011, DOI: 10.1016/j.jcsr.2011.03.029
Monotonic shear tests of CFS wall frames with sheathing
- C L Pan
- M Y Shan
Pan, C.L., Shan, M.Y.: Monotonic shear tests of CFS wall frames with sheathing, Thin-walled
Structures, Vol.49/2, pp. 363-370, 2011, DOI: 10.1016/j.tws.2010.10.004
Thermal insulation capacity of concretes by expanded polystyrene aggregate, The Fourth International fib Congress
- É Lublóy
- L Gy
- K Balázs
- E Kopecskó
- L Tóth
- P Dunai
- O Hegyi
- Drávucz
Polystyrene Aggregate Lightweight Concrete, Scientific Publications No. 15
- Gy Balázs
- K Kovács
- A Papp