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Experimental study on ultra-lightweight-concrete encased cold-formed steel structures Part I: Stability behaviour of elements subjected to bending

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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 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].

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... In modern constructions, cold-formed steel (CFS) structure systems have become increasingly used as alternates for common building materials like hot-rolled steel and reinforced concrete. The advantageous properties of this material, including its ease of fabrication, rapid assembly, and lightweight nature, have played a pivotal role in spreading such structures [1]. As load-bearing element, CFS exhibits failure modes related to stability, such as local, distortional, or global buckling and interaction. ...
... 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]. ...
Article
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.
... Section thicknesses of typically ranging from 1.2 mm to 3.2 mm, coldformed members have been fabricated with a common yield stress of 350 MPa up to 550 MPa [6]. The cold-formed steel (CFS) members are relatively easy method of manufacturing, beside the many advantages [3,2,6,7,17,18] such as (1)lightness, (2)high strength and stiffness, (3)fast and easy to transportation and install, (4) reduce delay due to weather, (5) no formwork needed, (6)easy to cut, (7)uniform size, (8)able to accommodate tolerance, (9)and that also has variety of shapes and configuration [2,3,4,6,7]. To take advantages the characteristics, the CFS used double C section with lipped channel as structural members usually produced to built-up section. ...
... Section thicknesses of typically ranging from 1.2 mm to 3.2 mm, coldformed members have been fabricated with a common yield stress of 350 MPa up to 550 MPa [6]. The cold-formed steel (CFS) members are relatively easy method of manufacturing, beside the many advantages [3,2,6,7,17,18] such as (1)lightness, (2)high strength and stiffness, (3)fast and easy to transportation and install, (4) reduce delay due to weather, (5) no formwork needed, (6)easy to cut, (7)uniform size, (8)able to accommodate tolerance, (9)and that also has variety of shapes and configuration [2,3,4,6,7]. To take advantages the characteristics, the CFS used double C section with lipped channel as structural members usually produced to built-up section. ...
... Section thicknesses of typically ranging from 1.2 mm to 3.2 mm, coldformed members have been fabricated with a common yield stress of 350 MPa up to 550 MPa [6]. The cold-formed steel (CFS) members are relatively easy method of manufacturing, beside the many advantages [3,2,6,7,17,18] such as (1)lightness, (2)high strength and stiffness, (3)fast and easy to transportation and install, (4) reduce delay due to weather, (5) no formwork needed, (6)easy to cut, (7)uniform size, (8)able to accommodate tolerance, (9)and that also has variety of shapes and configuration [2,3,4,6,7]. To take advantages the characteristics, the CFS used double C section with lipped channel as structural members usually produced to built-up section. ...
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Cold formed steel (CFS) of lipped C-Channel sections are commonly use because of their simple forming procedures and easy to erect. To improve the flexural strength of the proposed composite beam, the C-channel of Lipped section is arranged toe-to-toe to form into boxed shape section and filled with self-compacting concrete (SCC). Reinforcement bars was used in a tension zone to increase the flexural strength of the proposed beam in this experimental study. A U-shape re-bars was installed to act as shear connections between concrete slab and beam of boxed section filled with self-compacting concrete. Two specimens were prepared and tested until failure. A C-channel section of size 250mm deep, 75mm width, and 2.4mm thick was used for the proposed composite beam section. Longitudinal rebar's size of 16mm and 20mm were installed at the bottom of the beam encased by the self-compacting concrete of 50MPa. A U-shape re-bar if size 12mm in diameter was used as a shear connector and functioned as vertical shear resistance for the beam system. The beam is kept restrained in position by a profiled metal decking installed on top of the beam to form a slab system also cast using by SCC. The specimens were tested under pure bending arranged as simply supported beams. It was found that the moment resistance of the experimental results agreed well with the predicted numerical analysis.
... The applicability and efficiency of polystyrene aggregate concrete (PAC) encased cold-formed steel (CFS) elements was introduced in the first part of the paper [1], where the advantageous behaviour of PAC were also described based on previous research works [2,3,4]. In the first part the behaviour of flexural elements were presented, this paper deals with the behaviour due to axial compression. ...
... Similarly, as detailed in Table 3, the ultimate loads of braced elements are in a small region regardless of the element length (Table 4). Specimens with thicker steel plates showed slightly less increment, which agrees well with the finding in the case of beam elements [1]. The increments are in the same range as found previously, which suggests as beneficial behaviour as found in the first test series. ...
... During testing the specimen moved perpendicular to its plane, and finally produced a failure of interaction between bending and compression. The more compressed flange of columns inside PAC buckled as found in the case of beam elements [1] (Fig. 14 c)). This behaviour is caused by the global imperfections resulting from the concentrated load transmitting. ...
Article
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].
... These cost-effective building systems, distinguished by significant benefits such as light weight, fast fabrication, easy manufacturing, and absence of formwork, contributed to the widespread use of CFS elements in various applications. Consequently, CFS elements have become extensively used as primary load-bearing structures in pallet racks, industrial facilities, and residential buildings [1], [2]. Serving as load-bearing elements, CFS components exhibit distinct failure mechanisms regarding stability (i.e., local, distortional, global buckling and interaction). ...
... 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. ...
Article
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.
... These cost-effective structures, characterized by substantial advantages, such as their light weight, speed of production, ease of manufacturing, and no need for formwork, helped spread of these elements. Hence, CFS elements have become widely utilized as major load-bearing constructions such as pallet racks, industrial blinding, and residential houses [1,2]. ...
... 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. ...
Article
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.
... 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. ...
... . Finally, a general polynomial with simplified coefficients (6) has been proposed to provide the engineers with a handy equation to predict the stiffness of the foundation for any case within the investigated range of the parameters. Precisely, few suggestions have been tried out, and the one that gave the least error has been chosen as a final practical formula (6) for both internal and outstand compressed plate elements. ...
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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 ultimate load level was increased by 30-190%. Additionally, five specimens of floor panel tests were conducted which showed that "full bracing" was provided and the yield strength of steel core was exceeded [9]. Likewise, 57 member tests were conducted on both braced and unbraced members and three different element sizes to investigate the compression behavior. ...
Article
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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.
... Péter Hegyi [1] carried out an experiment test on a lipped cold-formed steel channel encased in polystyrene aggregate concrete (PAC) to examine the effect of different PAC mixtures on the compression capacity of the CFS as well as its effect on bracing the CFS. It was discovered that PAC was able to restrict global and distortional buckling and drove all specimens to fail owing to local buckling phenomena independent of CFS height. ...
... Various techniques are employed for stiffening CFS sections, with intermittent stiffening of webs and flanges being the most widely adopted [6][7][8][9][10][11]. Additionally, more advanced and intricate stiffening methods involve the use of corrugated webs in built-up sections during high-load situations, as they demonstrate superior performance in preventing buckling failures compared to flat webs [12][13][14][15][16], with triangular web corrugation being more effective than other profiles. Furthermore, other stiffening methods incorporate the use of external stiffeners [17,18], or stiffening materials like concrete [19][20][21] and lightweight materials like GFRP [22,23], timber [24,25], cardboard [25], high-density polystyrene [24]. Adopting partial stiffeners takes a different approach by strategically placing stiffening elements to enhance buckling stability in critical areas prone to buckling failure, rather than adopting the stiffener across the entire beam span [17]. ...
Article
This research paper presents a new flexural design approach for cold-formed steel (CFS) built-up sections failing in local buckling, developed following an extensive numerical investigation involving two novel closed built-up sections. At first, a finite element (FE) model using the widely adopted ABAQUS software was constructed and carefully validated against pertinent experimental data available in the literature. A comprehensive validation process which included comparing flexural strengths, deformed shapes, moment-curvature, and moment-displacement curves was performed. Afterwards, the validated FE model was extended to a numerical para-metric investigation comprising of 108 simulations involving both three-point and four-point bending cases. Key parameters, including cross-sectional shapes, slenderness, and screw spacing, were varied primarily to facilitate the formulation of the novel design method. The outcomes of this investigation revealed that the current direct strength method (DSM) available in the North American Specifications (NAS) underestimated the bending strength, particularly for the ultra-thin sections. Considering this observation which is consistent with the findings of past research on similar cross-sections, a Generalised Direct Strength Method (DSM-G) was developed by introducing a new mathematical model, which differs from the traditional slenderness limit equations, instead relying on a conservativeness degree-based approach used for modifying the original DSM equations. The DSM-G method demonstrated a better accuracy in predicting the flexural strengths of different built-up sections (including the ones investigated by other researchers), all failing by local buckling. Moreover, the reliability of DSM-G equations was assessed, satisfying the prescribed threshold index limit suggested in NAS. A comprehensive set of guidelines, along with a design example for implementing the DSM-G method, has been presented to facilitate practical application.
... Scholars in this field have conducted extensive studies on light-steel skeleton composite wallboards. Hegyi P. and Dunai L. [6] conducted vertical axial compressive tests on steel skeletons without polystyrene aggregate concrete (PAC) filling and cold-formed thin-walled composite wallboards with polystyrene aggregate concrete PAC filling. The ...
Article
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Foamed cement fly ash is a new type of lightweight construction material that can be combined with a light steel frame to form light-steel skeleton–cement–fly ash foam wallboard (LSSCFAFW). The research on the axial compressive performance of light steel and light concrete composite wallboard is relatively limited. Four pieces of LSSCFAFWs were manufactured, and the impact of stand column quantity and various filler parameters on the LSSCFAFW was investigated. The failure mode of the wallboard and the influence of different parameter variables on its axial compressive performance were obtained through experiments. Moreover, the test results indicated essentially the same damage patterns in terms of stand-column buckling, filler crushing, and self-tapping screw failure. The addition of polypropylene fiber to this wallboard can prevent filler from falling off. The axial compressive performance of the LSSCFAFW demonstrates a direct proportion with the number of columns and cement content, improving as the number of stand columns and the cement content increase. However, the addition of polypropylene fiber to the filler has a minimal effect on the axial compressive performance of this wallboard. Compared to the control group, increasing the number of stand columns, adding 0.4% polypropylene fibers, and increasing the cement dosage to 50% improved the ultimate bearing capacity of the wallboards by 12%, 8%, and 56% respectively. The result of this study can provide references for the research and application of light steel frame to form LSSCFAFW.
... 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. ...
Article
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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 a result, traditional concrete is unsuitable for developing lightweight CFS composite members. To overcome this shortcoming, some attempts were carried out to prepare lightweight concrete [32][33][34], but more research is needed to produce conclusive results for such composite elements. ...
Article
Although previous attempts for enhancing the buckling resistance of cold-formed steel (CFS) built-up beams through intermittent stiffening, external stiffening and adoption of concrete as composite sections were successful , they may compromise the lightweight constructional feature of these elements. This paper presents a test program aimed at developing CFS composite built-up beams with superior buckling performance and low self-weight for ensuring lightweight construction. Unlike concrete, lightweight stiff boards of timber and glass fibre reinforced polymer (GFRP) were sandwiched between the CFS channels in the web and flange region to construct the lightweight composite beams. All of the beam specimens were subjected to four-point bending with simply supported boundary conditions. Peak strength, load-deformation curves, initial stiffness, strength-to-weight ratios, failure modes and the normalized yield and plastic moment strengths were compared. This study established the structural feasibility of developing lightweight CFS composite built-up beams from timber and GFRP boards, indicating that the flexural strength and stiffness are significantly improved by 150% and 80%, respectively, as compared to the unstiffened CFS built-up beams. Moreover, the studied composite beams were shown to attain their full yield moment capacities, and in some cases more than 90% of their plastic moment capacity, resulting in built-up members with a higher structural efficiency.
... Previous research studies have successfully developed the concept of CFS concrete composite beams, which have exhibited desired flexural performance, as the CFS component was effective in resisting the tensile part of the flexure, while the concrete resisted the compression part [31][32][33][34][35][36][37][38][39][40]. This method of improving the buckling resistance of CFS sections looks highly promising, except that it takes away the important lightweight feature from the CFS construction. ...
Article
Previous attempts to develop lightweight cold-formed steel (CFS) composite sections have successfully improved their buckling strengths but have been limited to unstiffened profiles only. This paper reports the results of an experimental program on the flexural behaviour of newly developed CFSGFRP (Glass Fiber Reinforced Plastic) composite built-up open-section beams. In total, six large-scale specimens were tested under four-point loading with simply supported boundary conditions. To counter the inherent limitation of premature local buckling in the thin-walled CFS sections under compressive stresses, various combinations of intermittent stiffening and GFRP plank packing were adopted to improve the performance of the CFS GFRP lightweight composite beam specimens. The intermittent stiffening and GFRP plank packing were used judiciously in the compression flange and the web region of the specimens. A conventional open-section built-up beam was fabricated using two plain channels fastened through the web as a benchmark to evaluate the flexural performance of the composite beams. Furthermore, a hot-rolled steel beam with equivalent dimensions was also tested to give a broader comparison. The flexural performance of all the beams was assessed in terms of peak strength, initial stiffness, load-deformation response, failure modes and strength-to-weight parameter. The results confirmed the structural feasibility of adopting GFRP to form CFS lightweight built-up beams. The incorporation of GFRP planks significantly improved the flexural capacity by about 180% compared to the conventional CFS built-up beams. They also helped in attaining about 80% of the equivalent hot-rolled steel beam's flexural strength, resulting in highly efficient built-up beams for practical applications.
... 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. ...
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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. ...
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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.
... Through the full-scale indoor static load test of multi-cavity steel plate concrete composite floor, the ultimate bearing capacity and failure mode of composite floor were studied, and compared with other forms of precast composite floor; numerical simulation was carried out by ANSYS software. The mechanical properties of composite floor in the elastic stage were studied and compared with the test results; the influences of different steel plate thickness, composite floor thickness, cavity size and span on the mechanical properties of composite floor were analyzed by numerical simulation [11][12][13][14][15]. ...
Article
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This paper proposes a novel multi-cavity steel–concrete composite floor. The mechanical properties of multi-cavity steel–concrete composite floor were studied by static load test. Based on full-scale tests on 2500 × 1000 × 120 mm multi-cavity steel–concrete composite floors, the bearing capacity and failure characteristics of the composite floor were analyzed. Compared with the existing prefabricated floor, the reliability of the test was verified by finite element simulation. The influence of steel plate material thickness, floor thickness, cavity size and span on the mechanical properties of composite floor was analyzed. The results showed that the composite floor had stronger bearing capacity and better ductility and integrity than the existing precast floor. The bearing capacity and stiffness of composite floor were positively correlated with the thickness of steel plate and floor, and negatively correlated with the cavity size and span.
... These beams possess the following benefits: (1) The encased concrete is an effective structural support for the external CFS section, which is thinwalled so that the local buckling of the steel can be impeded for a while or possibly even completely prevented. This is in contrast to the H-section of the open steel found in the traditional steelconcrete composite beams for which the width to thickness ratio has to be constrained; (2) Together with the encased concrete, the external CFS is able to obtain a greater shear capacity which helps it avoid brittle shear failures; (3) The sections have no need for any temporary formwork for the in-filled concrete; this is because the steel plays the role of a formwork during the construction stage and as a reinforcement during the service stage [3][4][5][6][7]. ...
Article
In order to achieve greater ductility and strength, as well as to produce a more economical design, a novel composite beam and floor system have been developed to achieve higher strength and ductility, as well as to yield a more economical design purpose. This paper has put focus on this newly developed composite beam system which consists of a profiled metal decking slab made with self-compacting concrete (SCC). It has been joined cold-formed steel (CFS) built-up beams. These beams have been infilled with SCC by means of U-shaped rebar used as shear connectors. The researcher, in order to construct an open section, put together two CFS Clipped channel sections in a back-to-back formation, and to construct a closed section, the formation was made to be toe-to-toe. The flexural behaviour of the partly encased composite beam was evaluated through experimentation by the researchers. So that the researchers could observe the failure modes and flexural capacity of the construction, a four-point bending test procedure was performed on two samples taking into consideration both closed and open built-up beam sections. The results of the test demonstrated that the open sections were able to exhibit a 24 percent higher ultimate moment capacity as well as greater stiffness and higher vertical deflection. As can be seen from the results of the experimental bending test, the built-up design had a great impact on the capacity and deflection of the section, and the section that was encased was able to reach the ultimate strength when the proposed shear connector was placed in the composite action. In order to validate the present test results, the design and analysis of the new composite beams have been evaluated.
... 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 ...
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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]. ...
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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.
... Its low density and higher strength/weight ratio [4] are advantageous especially in case of slab structures. It can also be applied in Cold-Formed Steel structures (CFS), since the polystyrene aggregate concrete can provide continuous bracing [5]. This material is also resistant to biological degradation [6]. ...
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The aim of the paper is to investigate the hygrothermal properties of a newly developed ultra-lightweight polystyrene concrete, based on laboratory measurements. It describes the measuring process of thermal conductivities, and determines the declared thermal conductivity. The temperature and moisture conversion coefficients are determined, and new approximate functions are introduced. The paper describes the sorption and desorption isotherms, and gives polynomial approximate functions. The paper also investigates the temperature dependency of sorption curves. It determines the water absorption coefficient and the free water saturation. Furthermore, it describes the measuring process of the water vapor permeability. The water vapor resistance factor and water vapor diffusion-equivalent air layer thickness are calculated.
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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.
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In this study, a novel hybrid wall structure of a hot-rolled steel frame fabricated with a cold-formed steel (CFS) composite wall is proposed. Ceramsite concrete is lightweight concrete that is used in CFS composite walls. The seismic performances, including the failure mode, hysteretic behavior, shear capacity, stiffness, ductility, and energy dissipation performance, of four specimens of steel frame fabricated with CFS composite wall and one specimen of conventional CFS composite wall were evaluated under low-cyclic loading. The experimental results showed that the collaborative working performance of the steel frame and infilled CFS composite wall was optimum, and the proposed fabricated wall structure had a significant effect on the bearing capacity, stiffness, and energy dissipation capacity. The infilled CFS composite walls were damaged earlier than the steel frames. The damage was primarily characterized by the compressive failure at the corners of fillers, loss of diaphragm effect, screw connection failure, and bond-slip failure between the CFS framing and fillers. However, the steel frames exhibited no obvious damage, which effectively restrained the infilled CFS composite walls and prevented them from severe collapse. In addition, enhancing the strength of the fillers and increasing the section area of the studs improved the bearing capacity of the structure; however, they were detrimental to the ductility. Wall opening reduced the bearing capacity and initial stiffness of the structure; however, it improved the ductility. Furthermore, a superposition method was used to calculate the bearing capacity of the proposed structure. The calculated results showed a superior accuracy in comparison with the experimental results.
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Composite steel-concrete beams have been widely used in long span construction and high rise buildings due to their favorable behavior in terms of high strength, stiffness, and ductility. In this research, the flexural behavior of an innovative steel-concrete composite section is investigated experimentally and verified numerically using ABAQUS software. The studied section is composed of steel tubular specimen or steel hollow pipe totally encased in concrete in the absence of any flexural or shear reinforcement. Instead, steel mesh wraps are used around the tubular steel specimen to provide sufficient steel-concrete bond. All of the studied beams have the same 3m length and T-section dimensions to provide adequate comparison of results. The influence of using different percentages of steel mesh wraps around the steel specimen and the structural steel shape effect on the failure mode and ultimate flexural capacity were investigated. It was found that the ABAQUS model has provided excellent simulation of the flexural response of the studied beams with acceptable difference in results as compared to those obtained from experimental testing. Besides, the presence of steel mesh wraps at highly compressive damaged locations have prevented concrete spalling and crushing in these zones by ensuring sufficient steel-concrete bond.
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The use of thin-walled sections in the construction of residential and industrial buildings is very common. Thin-walled section elements are vulnerable to local buckling due to their slender nature. As a result, they will be unable to fulfil their minimum yielding capacity. Due to their high slenderness, mono-symmetric nature, eccentricity of shear centre, and low-torsional rigidity, they suffer from certain buckling modes due to their simple forming techniques and easy connectivity. Hence, it is necessary that these buckling modes are either delayed or eliminated to increase the ultimate capacity of thin-walled members. In multi-storey towers, where the Buckling Restrained Braces (BRBs) are thicker than the thin-walled portions, BRBs are widely used as lateral load resistant systems. The amount of strength required to prevent buckling of thin-walled parts would be less than that required by BRB. As a result, similar techniques cannot be employed due to the infill weight and tube sections involved. Therefore, a mechanism to avoid buckling must be created in order to enhance the efficiency and failure modes of such sections. The review comprises research that has been done to examine the consequences of buckling mode and its behaviour under various loading conditions. Buckling restraining the thin-walled part using UltraLightweightConcrete Composite (ULCC) can be used instead of BRBs. Keywords : Buckling Modes, Buckling Restrained Braces, Local Buckling Thin-Wall Member, Ultra-Lightweight Concrete Composite (ULCC).
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In the civil engineering field design of cost efficient is highly important. So we prefer cold-formed steel structures(CFS) for construction. An advanced CFS structure is implemented in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. Three cold formed built-up sections have been chosen, which are channel section connected back to back by welding, back to back channel section connected by welding and it is encased by Expanded Polystyrene beads(EPS) concrete and box section which is infill by EPS beads concrete. The project comprises the review of the existing literature on the flexural behaviour of cold-formed steel sections and testing of materials are conducted for cement, fine aggregate, lightweight aggregate (EPS). Mix design for EPS beads concrete also derived. The beam is to be experimentally tested under two-point loading and load bearing capacity of different sections will be compared. Keywords: cold-formed steel, polystyrene aggregate concrete, flexural behaviour, Mix design
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This paper studies the four-point bending response and failure mechanisms of sandwich panels with corrugated steel faces and either plain or fibre-reinforced foamed concrete core. Mechanical properties of both plain and polyvinyl alcohol fibre-reinforced foamed concrete were obtained, which are needed for the design of sandwich panel and numerical modelling. It is found that the fibre-reinforcement largely enhances the mechanical behaviour of foamed concrete and composite sandwich panels. Finite element code Abaqus/Standard was employed to investigate the influence of face/core bonding and fastening on the four-point bending response of the sandwich panels. It was found that face/core bonding plays a crucial role in the structural performance while the influence of fastening is negligible.
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The objective of this paper is to provide technical background and illustrative examples for stability analysis of cold-formed steel members using the conventional and constrained finite strip methods as implemented in the open source program CUFSM. Numerical stability analysis combined with an accurate identification of the buckling modes is an enabling first step in the implementation of new design methods such as the Direct Strength Method. In this paper conventional finite strip method analysis identical to that employed in CUFSM is derived from first principles. The methodology closely mirrors that of standard matrix methods for structural analysis, widely used by engineers, and can be readily programmed by the interested reader. An example of the stability solution for an industry standard lipped channel is provided. Recently, CUFSM has been extended to include application of the constrained finite strip method. Using formal mechanical definitions of the buckling classes: global, distortional, local, and other deformations, the constrained finite strip method can provide both modal decomposition and modal identification to a conventional finite strip solution. Modal decomposition allows the conventional finite strip solution to be focused on any buckling class (e.g., global, distortional, or local only), resulting in problems of reduced size and definitive solutions for the buckling modes in isolation, as demonstrated for an example section. Modal identification allows the results of a conventional finite strip solution to be judged with regard to the participation of the buckling classes; and thus provide a measure of buckling mode interaction. The conventional finite strip method combined with the constrained finite strip method provides a powerful tool for understanding cross-section stability in cold-formed steel members.
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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.
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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].
Article
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.
Experimental study on ultra-lightweight-concrete encased cold-formed steel structures, Part II -Stability behaviour of elements subjected to compression
  • L Dunai
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Dunai, L., Hegyi, P.: Experimental study on ultra-lightweight-concrete encased cold-formed steel structures, Part II -Stability behaviour of elements subjected to compression, Thin-Walled Structures, 2014 (under publication)
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 publications No. 15., Technical University of Budapest, 1975 (in Hungarian)
Special concretes III
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Balázs, Gy.: Special concretes III., Akadémiai Publisher, 2010, Budapest, Hungary (in Hungarian)
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Experimental study on ultra-lightweight-concrete encased cold-formed steel structures, Part II - Stability behaviour of elements subjected to compression, Thin-Walled Struct
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  • L Dunai
Thermal insulation capacity of concretes by expanded polystyrene aggregate
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