Abstract

     Weft-knitted textiles made from high-strength fibrous materials offer great potential for use as a flexible stay-in-place formwork and reinforcement system since they allow creating complex geometries (i.e. doubly curved or folded) and introducing spatial features such as ribs within the fabric. However, the closed surface of the textile and its placement at the bottom edge of the concrete element present major challenges regarding bond, which may lead to premature failure due to delamination of the reinforcement initiated by a substantial opening of a governing crack. This study investigates the influence of short integral glass fibres and spatial bond ribs on the mechanical behaviour of weft-knitted textile reinforced concrete elements subjected to bending and their potential to increase the shear resistance. To this end, an experimental campaign consisting of 14 four-point-bending tests was conducted, where the specimens were examined regarding their load-deformation behaviour, crack kinematics and failure modes. The contribution of the short glass fibres to the load-bearing mechanism was estimated with Pfyl’s fibre engagement model, based on the material characterisation results from prism tests on fibre reinforced concrete members.

Introduction

     The urgent need for the construction industry to reduce its ecological footprint has led to numerous advances to decrease the volume of concrete consumption. Thereby, the use of conventional steel reinforcing bars presents an intrinsic limitation for lightweight concrete structures due to the minimum concrete cover needed to protect the reinforcement from corrosion (between 20 and 50 mm depending on the regional building codes and exposure). Textile reinforcement allows minimising the thickness of the concrete elements to a few millimetres when using non-corrosive materials such as aramid, carbon or glass fibres [1]. The mechanical behaviour of such fibres is usually linear elastic with high strength (3000–4000 MPa) at a moderate to high stiffness (glass fibre: ca. 70 GPa; carbon fibre: ca. 240 GPa). Textile reinforcement typically consists of rovings formed from multiple filaments, which exhibit lower strength and stiffness than the individual fibres due to several reasons: (i) the failure mode is brittle and does not allow for redistribution of stresses within the roving cross-section once the weakest fibre reaches its tensile strength [2], [3], [4]; (ii) commonly used fibres are sensitive to lateral loading and may be damaged due to deviations at the crack edges [5], [6]; (iii) the loads are transferred via inter-fibre friction within the rovings, which leads to an inhomogeneous stress distribution over the cross-section [7]; (iv) while the ribs in conventional deformed steel bars provide a proper force transfer between reinforcement and concrete [8], the bond of textile reinforcement mainly relies on adhesion and friction [9], [10], [11]. Coating or even fully impregnating the rovings (e.g. with epoxy resin) can attenuate these effects and may significantly improve the mechanical performance of the textile reinforcement [12], [13], [14].

Conclusions

     This study investigated the influence of short integral glass fibres and spatial features to improve the structural performance of concrete beams with weft-knitted textile reinforcement attached to the bottom edge of the specimens, especially regarding their shear strength and their resistance against delamination of the reinforcement. To this end, an experimental campaign consisting of 14 four-point-bending tests was carried out. The mechanical behaviour was examined regarding the load–deflection curves, the stress–strain relationship of the textile reinforcement and the crack kinematics based on the digital image correlation measurements, following the methodology presented in [20] to assess the response of the tension chord for concrete members subjected to bending./

Highlights

Abstract

Keywords

1. Introduction

2. Experimental details

3. Results and discussion

4. Health hazards of ethylene acrylic acid co-polymer

5. Conclusion

Declaration of Competing Interest

Acknowledgements

References

Abstract

Bleached cotton fabric and a water-based polymer coating solution made from ethylene acrylic acid co-polymer which is multifunctional polymer material is used in this experimental study to increase the bending and thermal properties of cotton fabrics. Roller coating and Exhaust methods is used to apply ethylene acrylic acid co-polymer solution on the cotton fabric surface. The coated fabric surface is then cured and dried at a temperature of 60–90 °C using a laboratory oven. The developed fabric samples are then taken for testing for its bending and thermal properties using a fabric stiffness tester and DSC thermal analyzer. The chemical composition and its chemical group finger print analysis is also ascertained using FTIR spectra. The fabric stiffness results of coated fabrics show increased bending properties and the thermal property results from DSC and plotted graphs prove its robustness and resistance to heat. However, Roller coating method seems to be more efficient than exhaust method with respect to the application method employed for coating ethylene acrylic acid co-polymer.

1. Introduction

A water-based polymer coating solution, namely ethylene acrylic acid co-polymer which is multifunctional in nature is coated on bleached cotton fabric with an objective to enhance its bending and thermal properties in this study. The bleached cotton fabric is coated with ethylene acrylic acid by padding and exhaust bath process. In this experimental study, small soft rollers are used for padding the cotton fabrics using ethylene acrylic acid solution. Ethylene acrylic acid is multifunctional co-polymer and is mainly used for textile fabric coatings and many other applications which are of medicinal value, including packaging substrates. This liquid forms a thin film and binds uniformly to the substrate when applied on the surface externally. The liquid also finds many applications in cosmetics and commercial polymer thin film products. The liquid is colorless, with no foul odor and hence is used in many textiles and non-woven textiles. The solution has excellent sealing, adhesion properties coupled with its flexibility and special hardness [1].

Coating formulation and its application on fabrics is a complicated process. Many chemicals and polymer additives are used for coating, since adhesion and durability properties are also important for a coated fabrics. The quality of coating is also determined by the coating method and machinery used for coating. There are many techniques of coating that are used in finishing process. Some of them are done using knife-over-roller method, particularly used for polymer coatings that are solvent based, dip-coating for variety of water-based polymers and fabric treatments [11,12,18]. The chemical formulations are based on the functional properties that is desired and the level of ethylene acrylic acid is also determined keeping the health hazard parameters that ethylene acrylic acid can cause to human skin [13,14].

1- Introduction

2- Shake table tests

3- Numerical model

4- Measured and numerical results

5- Numerical study on seismic response of inclined tower legs

6- Influence of torsional stiffness

7- Conclusion

References

Abstract

More than half of cable-stayed bridges adopt the tower with inclined legs, which can be loaded with a combination of bending, torsion, shear and axial force under earthquakes. To study the seismic response of inclined tower legs, shake table tests were conducted on a 1/20 scaled cable-stayed bridge model with an inverted Y-shaped tower. A description of the model design was introduced and observed damages including horizontal and diagonal cracks at inclined tower legs were presented. A numerical model, considering reduction of torsional stiffness of inclined tower legs after diagonal cracking, was established. The feasibility of the numerical model was validated by a comparison of numerical and test results, which showed good correlation in displacement response at tower top and deck end, and cable force. Based on numerical results, the crack torsional moment of the inclined tower could be easily reached at small peak ground acceleration (PGA), leading to a substantial reduction of torsional stiffness of the section. This reduction helped alleviate the torsional moment demand at larger PGAs and delay the torsional failure of the tower legs. Numerical results also revealed that the bending moment is the primary factor to cause concrete cracks at the lower regions of inclined tower legs whereas complex interaction of large bending moment and torsion results in flexural and torsional damage near the intersection. Conventional ways, which adopt an elastic behavior of torsion, either using stiffness prior to or after diagonal cracking, will lead to intensive overestimation or underestimation of torsional response of the inclined tower legs.

Introduction

In recent decades, with the continual development in design methodology and construction technology, cable-stayed bridges have gained worldwide popularity in spanning large distance, probably up to 1000 m. The ability of a cable-stayed bridge to span such large distance owes much to its supporting system: the decks are supported by cables that are diagonally resisted by strong stiff towers. Acting as the main load-bearing element, the tower is of critical importance to a cablestayed bridge. In general, the tower should be designed to vertically resist large gravity load and also accommodate an amount of lateral loads associated with live loads, wind and seismic actions, and possible others [1]. The tower shape, by affecting load transmitting mechanisms, to some extent determines the success of a tower design. There are several tower shapes that have been successfully applied to practical engineering, namely H-shaped, A-shaped, inverted Y-shaped, single column, diamond-shaped and so forth. Fig. 1(a) shows the typical tower configurations of cable-stayed bridges. A detailed analysis of the bridge tower shape inventory of 70 existing cable-stayed bridges in China shows that approximately 1/3 of cable-stayed bridges utilized H-shaped tower and another 1/3 adopted inverted Y-shaped tower while the rest occupied the remaining 1/3 [2], as shown in Fig. 1(b). Also note that more than half of the bridges utilized the tower with inclined legs (including Y-shaped, A shaped, and diamond-shaped). The preference of the tower with inclined legs owes to the aesthetical appearance, efficiency and stability of the structure.

1- Introduction

2- Experimental methods

3- Experimental results

4- Analytical analysis

5- Finite element analysis

6- Application in residential stud walls

7- Conclusions

References

Abstract

Increasing awareness of environmental concerns is leading a drive towards more sustainable structural materials for the built environment. Natural fibres such as flax and jute have increasingly been considered for fibre-resin composites, with a major motivation for their implementation being their notable sustainability attributes. This paper is part of an ongoing effort by the author to demonstrate the structural properties of primary structural elements and members fabricated from natural fibre composites of flax and jute. Previously the structural properties of flat plates, plain channel sections and channel sections with complex stiffeners were investigated under pure compression. This paper presents investigations of channel sections with complex stiffeners under pure bending. A series of sixteen channels with varying geometries, complex stiffener arrangements and composite thicknesses were tested in pure flexure. Material tests indicated that the mean tensile elastic stiffness and strength values were 6386 MPa and 55.1 MPa for flax, and 6941 MPa and 62.1 MPa for jute. The experimental results indicated that flexural failure of the channel sections was governed by tensile fracturing. The ultimate moment capacities varied from 1.043 to 1.501 kNm for four-layered composites, and 2.184 to 2.511 kNm for six-layered composites. The analytical models predicted the experimental ultimate moment capacities well, with a mean and coefficient of variation of the test to predicted ratio of 0.97 and 0.06, respectively. Finite element models used progressive damage analysis via stress-based damage initiation models and damage evolution laws, to replicate the tension fracture failure mode of the channels. The numerical models predicted the experimental ultimate moment capacities well, with a mean and coefficient of variation of the test to predicted ratio of 0.99 and 0.06, respectively.

Introduction

Public concerns about the environment, climate change, energy consumption and greenhouse gas emissions are driving demand for the use of sustainable materials in the built environment. There has been substantial attention given to the use of natural fibres in fibre-reinforced plastics in recent decades, where such fibres may be combined with thermoset or thermoplastic polymers to create natural fibre composites. Such natural fibre composites have particularly been identified for their favourable sustainability properties, including for example: renewable resource; carbon sink; short growth cycle time; low herbicide requirements due to rapid growth; low energy production; recyclable; biodegradable; and low hazard manufacturing and composite handling and working [1-7]. Much of this research has been from a materials science standpoint, assessing materials aspects such as fibre processing techniques, composite fabrication methodologies, matrix materials and their effects on the mechanical properties [8-13]. This research has indicated that composites consisting of natural fibres have general characteristics similar to their synthetic fibre counterparts, such as glass and carbon, however have comparably low intrinsic mechanical properties [2-13]. As a result, identifying structural applications such as those in civil infrastructure have thus far been limited [14-22].

1- Introduction

2- Experimental program

3- Test results and discussion

4- Effect of section size on moment capacity

5- Conclusions

References

Abstract

It has been shown that as concrete strength increases, the size effect becomes more pronounced in both samples and members. However, the effect of section size on the seismic performance of high-strength reinforced concrete columns requires further confirmation. For this purpose, six high-strength reinforced concrete columns were subjected to monotonic and cyclic loading in this study. The experimental results indicate that the relative nominal flexural strength, average energy dissipation coefficient, factor of safety, and local factor of safety all exhibited a strong size effect by decreasing as the column size increased. Moreover, the size effect on the factor of safety was stronger for high-strength columns than for conventional columns. The observed changes in the factor of safety were in good agreement with the Type 2 size effect model proposed by Bažant; so, using the local factor of safety and Bažant’s Type 2 model, the code equation for moment capacity was modified to provide a constant factor of safety regardless of column size.

Introduction

As the scale of engineering structures increases, the safety of their larger components has become one of the primary topics of concern, especially when taking into account the use of high-strength concrete [1]. The size effect, defined as the change in structural behavior with changing size rather than material, though not yet captured by the conventional design process, is increasingly accepted in theory [2–10]. Indeed, a large number of experimental results have demonstrated that the size effect exists in plain concrete samples and structural concrete components, such as plain concrete columns [11,12], reinforced concrete (RC) beams [13–15], RC columns [16–18], and RC beam-column joints [19–20]. Moreover, the size effect has been found to be more significant in high-strength concrete than in conventional concrete [1,12,21,22], but the size effect on the seismic performance of highstrength RC columns remains to be determined. In this study, the classical model of the size effect law was first investigated so that the correct theoretical model could be applied to a structural design. The scaling problem of primary interest is the effect of a structure’s size on its nominal strength [2]. The structural ultimate load predicted by any deterministic strength theory (e.g. the elastic, plastic, or elastoplastic strength criteria) applied to ductile materials exhibits no size effect. In 1921, Griffith [3] proposed linear elastic fracture mechanics (LFEM) and introduced fracture mechanics into the study of size effect. For brittle, geometrically similar structures, linear elastic fracture mechanics shows that nominal strength decreases as structure size increases, following the trend of an inclined asymptote with a slope of −1/2. Then Weibull [4,5] derived an equation capturing the size effect on mean structural strength based on the Weibull distribution. This approach is certainly valid for various fine-grain ceramics and for metal structures embrittled by fatigue. Bažant identified the Type 1 size effect [2,8], the Type 2 size effect [6], and the universal size effect law [9]. These laws are suitable for quasi-brittle materials, such as plain concrete samples and components, whose properties are between those of ductile and brittle materials.

1- Introduction

2- Experimental details

3- Results and discussion

4- Conclusions

References

Abstract

This paper presents the influence of the off-axis angles on the flexure behaviors of three-dimensional (3D) woven carbon/epoxy composites. Four kind of samples with different angles, 0 degree, 30 degree, 45 degree and 90 degree, are experimentally tested via three-point bending method. The immersion focused ultrasound imaging and micro-computed tomography (Micro-CT) techniques are employed to investigate the deformation and damage mechanisms in the specimens fractured in bending. Results indicate that the stress-deflections of on-axis (0 degree and 90 degree) samples exhibit obvious quasi-brittle behaviors, whereas those of off-axis (30 degree and 45 degree) samples show important ductile features. Furthermore, the dominant failure mechanism of on-axis samples are identified to be inter-ply delamination and fiber bundle fractures, whereas those of off-axis samples are matrix cracks and tows debonding.

Introduction

3D woven preforms and their composites as structural components are being used increasingly for the aircraft and space applications owing to their excellent out-of-plane properties for delamination resistance and impact damage resistance [1-3]. In the past few years, researchers have mainly focused on the in-plane mechanical behaviors, while the bending large-deformation and failure mechanisms are still systematically unclear. This can be attributed to the variability and complexity of the microstructure, and the limitation of the experimental technology. Furthermore, 3D woven composites are highly anisotropic, leading to the obvious orientation-dependence. In practice, 3D woven composite materials acquire the load carrying capacities not only along the two principal directions coinciding with the warp and weft axes, but also along any other bias directions. Consequently, an improved understanding of the off-axis bending behaviors and failure characterizations of 3D woven composites will be helpful for researchers in designing and constructing the high-performance materials.

This study investigates the potential of fine particles of recycled construction and demolition waste (CDW) aggregate to undergo alkali-activation when mixed with an appropriate alkaline solution. The fine is a natural by-product of the milling process and includes particles from four main material sources (i.e., recycled concrete, recycled asphalt, crushed bricks and tiles, and natural aggregate and excavated soil) and other occasional elements which are too small for identification. The fine was obtained by sifting the material through a 125 mm sieve. Since the reactivity of unselected material depends on its constituents, these were also individually investigated. Firstly, the four constituents of CDW recycled aggregates were separated, then milled to a size smaller than 125 mm, before being tested to measure their reactivity to an alkaline solution. A preliminary chemical and mineralogical characterization of the five powders was carried out to identify the main crystalline phases and ascertain the presence of aluminosilicates needed for the alkali-activation process. Particles of each powder were afterwards mixed with three concentrations of the same alkaline solution with a liquid/solid mass ratio of 0.4, cast in prismatic moulds, and cured at room temperature. Mechanical tests after 3, 7, and 28 days of curing demonstrated that powders react positively in a basic environment, showing an increase in strength without any thermal treatment. Hardened pastes of undivided fine aggregate and recycled asphalt exhibited the best results in terms of flexural and compressive strength with the more concentrated solution. A Field Emission Scanning Electron Microscopy analysis was also carried out to observe the microstructure and to support an interpretation of the mechanical strength data. Results demonstrated the feasibility of using a solution to activate unselected CDW fine particles to stabilize CDW aggregates. In full scale applications, CDW aggregates can be stabilized without the addition of any binder.

Introduction

The continuous production of waste from construction and demolition activities is a major environmental concern in European countries. EU Commission estimates reveal that construction and demolition waste (CDW) accounts for approximately 25e30% of all waste generated in Europe (European Commission, 2011). Several researches have demonstrated the potential for the reuse of this waste as an alternative material in civil engineering (Cardoso et al., 2016; Contreras et al., 2016; Vieira and Pereira, 2015). This is due to the presence of solid particles from a variety of construction materials which can form new aggregate grains of variable toughness and hardness, depending on composition, which in turn is conditioned by the type of construction and/or demolition work. In fact, an unselected CDW usually includes constituent materials in different proportions including (recycled) concrete fragments (RC), ceramic products such as crushed bricks and tiles (BT), reclaimed asphalt pavement grains (RA), natural aggregates and excavated soils (NA), together with occasional small particles of glass, wood, metals, and plastic (Jimenez, 2013
). Member states are being encouraged by the European Directive 2008/98/EC (European Parliament, 2008) to increase the use of recycled non-hazardous waste resources in place of natural materials to a minimum of 70% (by weight) by 2020. Consequently, construction activity has witnessed the increased use of alternative materials and recycled aggregate from CDW in numerous civil works (Vandecasteele et al., 2013).

Current design and assessment guidelines define several seismic performance levels, aiming to ensure that structures exhibit adequate behaviour at different seismic intensity levels. Typically, the acceptance criteria at different performance levels are met by ensuring that local deformation demands are lower than pre-defined capacities. Despite the proven effectiveness of such an approach, it provides an ambiguous measure of the performance of the building, which, in most cases, is neither meaningful nor appropriate for building owners, stakeholders or decision-makers. The main objective of the research presented in this paper is to evaluate the expected direct economic seismic losses of steel moment-resisting frame structures designed according to Eurocode 8 (EC8). A set of 120 archetype buildings, representative of the current building stock in Portugal, were designed according to Part 1 of EC8 using three different behaviour factors, q: a) code-prescribed upper bound limits for medium and high ductility classes; b) behaviour factor defined according to an Improved ForceBased Design (IFBD) procedure. The PEER-PBEE methodology with the improvements proposed by Ramirez and Miranda [1] was employed for the estimation of expected seismic losses evaluated for the seismic intensity levels considered in Part 3 of EC8. The results obtained indicate that the buildings designed in accordance with EC8 comply with the non-collapse criteria. However, the level of damage could imply significant repair costs. Importantly, the results also highlight that a rational selection of the behaviour factor can result in a reduction of steel weight but still ensuring acceptable levels of expected annual losses.

Introduction

Current seismic design guidelines allow for the inelastic behaviour of the structure to be explored during the design earthquake intensity level and, therefore, some degree of damage is therefore expected to occur. Although this is acceptable from an engineering point of view, given the ductile nature of structures designed according to modern provisions, stakeholders and building owners generally perceive that seismic design ensures both the safety and the development of minor damage levels for any seismic intensity level. It is therefore crucial to provide meaningful metrics of seismic performance (e.g. expected levels of earthquake-induced economic losses, fatalities, business interruption time, etc.) to support the decision making process of these agents in order to help stakeholders and building owners to take an informed selection of design options. Seismic design according to current practices and standards aims, primarily, at the protection of life-safety, with a heavy focus on strength control, incorporating comparatively minor provisions for deformation and damage control [1,2]. However, even though code design procedures seek to ensure that buildings meet certain levels of seismic performance, the actual performance is not normally assessed throughout the design process [3]. The concept of performance-based design was firstly introduced in Vision 2000 [4] after the 1994 Northridge and 1995 Kobe earthquakes. In these earthquakes, even though most structures exhibited acceptable non-collapse performances, there were high financial losses due to downtime, damage on non-structural components and losses/damage in building contents.

The piled-raft is a geotechnical foundation consisting of the three elements raft, piles and soil. Burland (1977) proposed that the piles can be used to reduce the settlement of the raft foundation. In piled-raft foundation, the total load of the superstructure is partly carried by the piles and the raft. The distribution of total load among the piles, raft and soil depends on their relative stiffnesses. Based on the dimensions of the raft and piles, the piled-raft has been classified as a small piled-raft (Br/Lp < 1) and large piled-raft (Br/Lp > 1) (Viggiani, 2001; Sanctis and Mandolini, 2006; Mandolini et al., 2013). In a small piled-raft, the flexural stiffness of the raft is usually high and the differential settlement does not represent a problem. Here, the primary reason to add the piles is to achieve a sufficient factor of safety against the bearing failure. However, in a large piled-raft, piles are added essentially to reduce the settlement. Poulos (2001) indicated that the 3-D numerical modeling is the most reliable method for the analysis of the piled-raft foundation in a clay soils. The maximum settlement, differential settlement, raft bending moments and shear force, axial loads and pile bending moments are considered as crucial parameter for optimum design of piled-raft foundation. Several researchers have been investigated the settlement (Prakoso and Kulhawy, 2001; Cho et al., 2012; Sinha and Hanna, 2016) and bearing behavior (Reul, 2004; Sanctis and Mandolini, 2006; Lee et al., 2010) of a piled-raft foundation on clay soils by numerical modeling. Oh et al. (2008) conducted a study on the piled-raft foundation in sandy soil by numerical modeling. They reported that with increase in raft thickness and pile spacing, the bending moment of the piled-raft increased. The different design aspects of the piled-raft foundation have been reported by Seo et al. (2003), and Reul and Randolph (2004). Ghalesari et al. (2015) suggested that the piled-raft foundation can be adopted as offshore foundation to reduce the settlement and to enhance the bearing capacity of the foundation. Furthermore, Poulos and Devdas (2005), Poulos and Bunce (2008), Poulos et al. (2011), Rabiei and Choobbasti (2016) indicated that the piled-raft can be used as an effective and economic foundation alternative for tall buildings to control the settlement and to enhance the bearing capacities. In addition to this, Nguyen et al. (2014) conducted a parametric study of large piled-raft foundations in sandy soil through finite element modeling. They indicated that the concentrated pile arrangement method can help to considerably reduce the settlements and bending moments of the raft. However, very few parametric studies by means of numerical modeling have been reported for the large piled-raft foundation on a clay soils. Therefore, the effect of different parameters on large piled-raft foundation needs to be investigated. The intended large piled-raft foundation can be used for the construction of residential or commercial buildings situated near onshore line where mostly undrained conditions prevail.

The lateral force resistant ability of high-rise building is very essential in its design. The lateral force resistance of common frame structures could be significantly improved by adopting steel plate shear walls (SPSWs), and this technique has been utilized in practical engineering structures worldwide. Yet, some disadvantages exist in the frame structures with SPSWs as follows: (1) Generally, out-of-plane bending rigidities of steel plates are quite small, especially for those with small thickness. Hence, when the SPSW is subjected to lateral forces induced by earthquake or wind effects, it easily buckles and its post-buckling strength would be produced through yielding of the diagonal tension field, leading to a loud noise. (2) For the structure with its frame and SPSWs installed simultaneously, the vertical loads transmitted from upper structures would be applied to the SPSWs, thus producing pre-compression and influencing the shear resistance of the SPSWs [1]. With those considerations, the infilled steel plates could commonly be replaced by steel corrugated plates, forming the steel corrugated shear walls (SCSWs). Numerous investigations were conducted by researchers to perform the comparison of the shear resistance and hysteretic behavior between SPSWs and SCSWs [2–6]. Berman et al. [2,3] performed the comparison of hysteretic performances among SPSWs, ordinary concentrically braced frames (OCBFs) and SCSWs, in which the corrugations were set in a diagonal direction with an inclination angle of about ° 45 . Emami et al. [4,5] conducted hysteretic tests of SPSWs and SCSWs, in which the corrugations installed horizontally and vertically were respectively considered. Kalai et al. [6] conducted FE analyses of SPSWs and SCSWs under cyclic shear loads to perform comparison, in which the effect of corrugation shapes on the hysteretic performances of SCSWs was investigated. According to these researches, by utilizing SCSWs in frame structures, the shear buckling loads could be significantly promoted owing to the increase of bending rigidities of the steel corrugated plates. In addition, based on the investigations performed by Tong and Guo [7], the vertical pre-compression loads could be efficiently released for the SCSWs with their corrugations laid horizontally. Due to these advantages of SCSWs, they have been widely used in practical building structures as lateral force resistance systems in recent years, as shown in Fig. 1. Current researches on SCSWs mainly focused on the shear resistance of SCSWs with small thickness (i.e. t = − 0.5 1.5mm), and numerous experimental and numerical investigations have been published [8–16]. The SCSWs with small thickness are easily to be profiled into trapezoidal corrugations. However, they are only suitable for the applications in low-rise buildings since the thickness of SCSWs inevitably limits their upper bound of shear resistance. In order for the applications of corrugated plates with small thickness in high-rise buildings, multiple corrugated plates would be required to improve the ultimate resistance. Otherwise, SCSWs with large thickness (i.e. t = −4 8mm) should be adopted in high-rise buildings, which benefited from both the improvements of the steel ductile properties and the equipment for cold rolling. Correspondingly, the shear resistant behavior of SCSWs with large thickness is worth of investigation for high-rise structural applications.

Nowadays, in the light steel framing construction industry, individual profiles with different cross-section shapes (C, U, R, etc.) are used to fabricate built-up members. A built-up coldformed steel (CFS) structural member can span more distance and present higher load bearing capacity and torsional stiffness. Moreover, usually, built-up members are symmetric, eliminating eccentricities between shear and gravity centers, leading to improved member stability. Built-up cross-sections are built fastening individual profiles with self-drilling screws or alternatively using seam weld (Stone and Laboube, 2005; Li et al., 2014; Wilson and Guzmán, 2011). Research has been focused mainly on open sections such as plain and lipped channels, with simple and complex edge stiffeners, with and without holes and angles (Young and Rasmussen, 1998a; Young and Rasmussen, 1998b; Kesti and Davies, 1999); however, in the past few years, some research on the behaviour of built-up CFS members has been conducted (Georgieva et al., 2012; Yuanqui et al., 2014; Young and Chen, 2008). Currently, the effective width method (EWM) is used worldwide, and the direct strength method (DSM) (Schafer, 2008) is used in North America, for design of CFS structural elements. Design guidelines in EN 1993-1-3 (2004) for built-up members are still vague. For instance, the EN 1993-1-3 (2004) only predicts that the buckling resistance of closed built-up members should be determined using the buckling curve b in association with the basic yield strength fyb and buckling curve c in association with the average yield strength fya if Aeff = Ag. In fire situation, the design methods presented in the EN 1993-1-2 (2005) for hot-rolled steel members are also applicable to CFS members with Class 4 cross-sections, establishing the same reduction factors for the mechanical properties of hot-rolled and CFSs. Some studies show that the reduction factors for CFS (Outinen, 1999; Kankanamge and Mahendran, 2011; Ranawaka and Mahendran, 2009a) are different from those prescribed in EN 1993-1-2 (2005). Also, the EN 1993-1-2 (2005) for Class 4 cross-sections limits the critical temperature to 350°C, which may be overly conservative if the load ratio is not considered (Ranawaka and Mahendran, 2009b; Heva, 2009). Moreover, there are no specific design guidelines regarding the influence of restrained thermal elongation in the overall behavior of CFS columns in fire. Several studies on this matter were already conducted but for heavy hot-rolled steel columns (Franssen, 2000; Ali and O’Connor, 2001). The great majority of the conducted research on the fire behaviour of CFS columns has been focused on the local and distortional buckling phenomena using both experimental and numerical analysis (Feng et al., 2003a, 2003b; Lee, 2004; Ranawaka and Mahendran, 2006).