This paper evaluates the strength of unlipped channel columns using the Direct Strength Method (DSM), which applies to the sections with either intermediate or edge stiffeners. The local buckling ...behaviour of plain cold-formed steel sections (CFS) with fixed-ends is studied by investigating the results of (i) 25 experimental studies published in the literature and (ii) a numerical study of 105 CFS sections. This paper reveals that the aspect ratio (web height to flange width ratio) of the cross-section significantly affects the local buckling strength of plain unlipped channel sections. The DSM local buckling strength as specified in the codes of practice ignores the effect of this parameter, resulting in unconservative designs for such columns. The difference in strength prediction can be up to about 15% for columns with a web height to flange width ratio of 3.0. At this aspect ratio, the inter-element stiffness contribution in the post-buckling stage is the minimum, resulting in a lower strength estimation. To account for this inadequacy, this paper suggests a modified DSM design procedure that accounts for the effect of stiffness contribution from the aspect ratio of the cross-section in the post-buckling stage. The proposed modified DSM design equations agree well with the results of experimental and numerical studies and preserve the target reliability of AISI- S100 (2016) for LRFD.
During bushfires, one of the building elements that is directly exposed to embers, radiant heat and direct flames is the “wall” element. This study investigated the feasibility of using expanded ...perlite aggregate in masonry (i.e., cement) blocks to enhance their bushfire resistant characteristics. The chemical, physical, and thermal properties of expanded perlite aggregate were determined first and then masonry block cement mixes were developed by replacing sand in the conventional mix with expanded perlite aggregate by volume at different percentages (100, 80, 60, and 40%). The properties of fresh and hardened cement mixes (slump, density, compressive strength, and water absorption) were measured. The developed masonry blocks were exposed to Bushfire Flame Zone conditions (i.e., 20–842 °C) and the standard fire curve for three hours (i.e., 20–1110 °C) to assess their resistance to bushfires and building fires, respectively. The properties of Cement–Expanded Perlite mixes were compared with those of the standard Cement–Sand mix. The test results showed that the use of perlite aggregate reduced the workability, density, and compressive strength of the cement mix while increasing the water absorption and fire resistance level. All the developed perlite blocks were lightweight and had three hours of fire resistance level (-/180/180). When exposed to bushfire flame zone conditions, the blocks made with 100, 80, and 60% perlite satisfied the maximum ambient surface temperature limit. Of these, masonry blocks made with 60% perlite aggregate are the most suitable for use in external walls of bushfire shelters and residential and commercial buildings in bushfire-prone areas.
The use of light-gauge steel framed (LSF) wall systems in low- and mid-rise buildings has increased due to the fast and clean construction and robust structural performance. Cold-formed steel studs ...used as the primary load-bearing component in LSF walls are often subjected to combined axial compression and bending actions caused by loading eccentricity. Research on the effects of loading eccentricity on the compression capacity has been limited while the currently used AS/NZS 4600 and AISI-S100 DSM design guidelines significantly underestimate the load bearing capacities. In this study, 35 lipped channel columns of 0.6 to 1.5 m lengths were tested under concentric and varying levels of eccentric axial compression loading and the resulting load versus axial shortening curves and failure modes were analysed. Non-linear finite element models of tested columns were developed and validated using the test results. Comparison of the ultimate capacities obtained from the tests and finite element analyses against those predicted by the DSM design guidelines showed that the current DSM design guidelines underestimate the capacities whereas a closer agreement was obtained from the improved DSM design guidelines proposed in a recent research study. This paper recommends the improved DSM design method to enable economical and safe designs.
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•Conducted concentric and eccentric axial compression tests of 35 thin-walled and high strength lipped channel sections.•Proposed a new test setup using a clamping mechanism for conducting eccentric compression tests of columns.•Developed and validated FE models of lipped channel sections subject to large loading eccentricities up to 75 mm.•Investigated the accuracy of current and proposed DSM beam-column equations for thin and high strength lipped channels.•Demonstrated the benefits of the new DSM for sections buckling in local, distortional, local-distortional and global modes.
•Conducted tests to determine post-fire mechanical properties of cold-formed steel hollow sections.•Determined post-fire mechanical properties of hollow sections of different grades and ...thicknesses.•Test results did not agree with those obtained from previous studies and design standards.•Proposed suitable equations to predict post-fire mechanical property reduction factors.•Strength enhancement techniques were proposed for fire damaged hollow sections.
Cold-formed steel hollow sections are extensively used in building construction due to their potential benefits over hot-rolled and open cold-formed steel sections. Their performance in fire is important for successful structural applications while their post-fire residual capacities are also important to assess the extent of their fire damage and reusability with and without strength enhancing techniques. This paper presents the details of an experimental investigation on the post-fire mechanical properties of cold-formed steel hollow sections. Tensile tests were performed on coupons exposed to elevated temperatures varying from 100 to 800 °C and then cooled down to room temperature. These coupons were cut from cold-formed steel square and rectangular hollow sections with varying thicknesses and grades. The results from this investigation provided post-fire stress-strain curves, yield strengths, ultimate strengths and elastic modulus, and their reduction pattern. They show that the post-fire mechanical properties of cold-formed steel hollow sections are different to those of open cold-formed channel and hot-rolled sections. New predictive equations were proposed to determine the post-fire mechanical property reduction factors. Post-fire mechanical properties were also compared with their elevated temperature mechanical properties to evaluate their strength gain after cooling down. This paper also evaluates various strength enhancement techniques for use with fire damaged cold-formed steel hollow sections.
Cold-formed steel members are widely used in residential, industrial and commercial buildings as primary load-bearing elements. During fire events, they will be exposed to elevated temperatures. If ...the general appearance of the structure is satisfactory after a fire event then the question that has to be answered is how the load bearing capacity of cold-formed steel members in these buildings has been affected. Hence after such fire events there is a need to evaluate the residual strength of these members. However, the post-fire behaviour of cold-formed steel members has not been investigated in the past. This means conservative decisions are likely to be made in relation to fire exposed cold-formed steel buildings. Therefore an experimental study was undertaken to investigate the post-fire mechanical properties of cold-formed steels. Tensile coupons taken from cold-formed steel sheets of three different steel grades and thicknesses were exposed to different elevated temperatures up to 800°C, and were then allowed to cool down to ambient temperature before they were tested to failure. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield stress, Young׳s modulus, ultimate strength and ductility). It was found that the post-fire mechanical properties of cold-formed steels are reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 300°C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of cold-formed steels. Such post-fire mechanical property assessments allow structural and fire engineers to make an accurate prediction of the safety of fire exposed cold-formed steel buildings. This paper presents the details of this experimental study and the results of post-fire mechanical properties of cold-formed steels. It also includes the results of a post-fire evaluation of cold-formed steel walls.
•Experimentally investigated post-fire mechanical properties of cold-formed steels.•Cold-formed steels regain 85% of the original elastic modulus after being exposed to temperatures below 800°C.•They regain 80% of the original yield strength after being exposed to temperatures below 500°C.•Proposed a new set of equations to predict post-fire mechanical properties of cold-formed steels.•Conducted a post-fire evaluation of LSF walls.
Cold-formed steel (CFS) roof and wall cladding systems comprising thin, high strength steel battens and claddings are popularly used in the building industry worldwide. These cladding systems have ...been observed to encounter failures under combined snow and strong wind actions during blizzards. Significant damage is caused by the disengagement of the entire roof/wall cladding when localised pull-through failures occur in thin-walled steel battens at the batten to truss/rafter screw connections due to a splitting mechanism around the screw head. This study uses detailed finite element analyses of the pull-through failures of a range of batten configurations under combined wind and sub-zero temperature conditions. Suitable finite element models capable of simulating the pull-through failures of battens were developed and validated using experimental results, followed by detailed numerical parametric studies. The main outcomes of this study are accurate design equations and capacity reduction factors essential for predicting the pull-through capacities of CFS battens at sub-zero temperatures.
•Investigated the splitting caused pull-through failure of thin battens under wind suction loading at sub-zero temperatures.•Developed numerical models with suitable failure criterion for varying batten configurations and sub-zero temperatures.•Numerical models were validated and used in a parametric study to identify key parameters affecting pull-through capacity.•Existing cold-formed steel design equations were found to be inadequate.•New design equations were proposed for the pull-through capacities of batten screw connections at sub-zero temperatures.
•Investigated the effects of geometric imperfections on the capacities and failure modes of eccentrically loaded studs.•Used simple single stud FE models to investigate the behaviour of sheathed LSF ...walls under eccentric compression.•Developed an advanced FE model for LSF wall panels by including sheathing, tracks and screw connections.•Validated the advanced model through comparison of failure modes, capacities and load-displacement curves from experiments.•Highlighted the benefits of using advanced numerical modelling over basic single stud modelling for LSF walls.
The current numerical studies and design of light-gauge steel framed (LSF) wall and floor systems are largely confined to individual members with idealised boundary conditions. Idealised single stud models of LSF walls that have been extensively used in the past are unable to capture the complex behaviour associated with stud-to-sheathing and stud-to-track connections. The ultimate capacities and failure modes predicted by these models may not always be accurate because of which designers have to resort to expensive and time-consuming full-scale testing. Advanced numerical models that explicitly model all LSF wall components are available in recent literature. However, they are limited to LSF walls under axial compression. In this study, the behaviour of LSF walls made of lipped channel studs under eccentric axial compression was investigated by developing a sheathed stud model simulating the sheathing material, tracks and connections using ABAQUS. This advanced model incorporated material and geometrical non-linearities, contact interactions, non-linear behaviour of stud-to-sheathing connections and explicit modelling of gypsum plasterboard sheathing, and was validated using experimental results. The failure modes, ultimate capacities and load versus axial shortening and lateral deflection curves predicted by the advanced model were compared with those predicted by the simple single stud models and suitable recommendations were proposed for finite element modelling of LSF walls under combined loading actions. This paper presents the details of the development of advanced models of LSF walls subject to compression and bending actions and its findings.
•Investigated the effects of screw restraints on the distortional buckling behaviour of LSF walls.•Investigated the accuracy of numerical methods and idealised screw restraints on distortional ...buckling.•A detailed parametric study was conducted using a validated sheathed stud FE model.•Investigated the effects of screw connections and stud slenderness on the distortional buckling capacity.•Developed improved DSM design methods for the distortional buckling capacity of LSF walls.
With the new advancements in constructions technologies, the use of cold-formed steel (CFS) construction is becoming popular due to its inherent advantages over conventional construction materials. These high performing CFS sections, such as the web stiffened lipped channel studs, are more likely to be subjected to distortional buckling under compression load. Although many numerical and experimental studies have been undertaken on unsheathed CFS columns subjected to distortional buckling, there is limited research on light gauge steel framed (LSF) walls subject to distortional buckling. The behaviour of sheathed wall studs is significantly different to that of columns due to the complicated boundary conditions provided by the stud-to-sheathing contact interactions and screw connections. Although CFS design standards recognize the sheathing boards as a means of providing lateral and rotational restraints, they do not provide any information on their effects on studs subject to distortional buckling. In this study, the suitability of currently available numerical modelling techniques on predicting the distortional buckling behaviour of LSF walls was investigated. It was identified that the distortional buckling capacity is highly sensitive to the in-plane restraints provided by screw connections. The effects of stud geometry, stiffness of screw connections and stud length on the distortional buckling capacity were investigated in a detailed numerical parametric study involving more than 3500 finite element analyses. Finally, the accuracy of the current direct strength method was investigated and suitable modifications are proposed. Moreover, alternative simplified design methods and their accuracy are also discussed.
Cold-formed steel (CFS) roof and wall cladding systems are used worldwide, and are constructed using high-strength, thin steel battens and claddings. In North American countries, which are frequently ...subjected to blizzards (winter storms), these cladding systems are particularly vulnerable to pull-out failures during combined windstorm and snowy conditions. Despite extensive research studies investigating the pull-out failure mechanism and the critical parameters of screw connections between cladding and battens at ambient temperature, the behaviour of these connections under blizzard conditions has not been experimentally investigated. To fill this knowledge gap, an experimental study was undertaken that included 144 laboratory tests of screw connections in battens of varying grades and thicknesses, and three distinct types of screws. The pull-out failure capacities of screw connections in battens were evaluated under wind suction loading at four different temperatures, including ambient and sub-zero temperatures. The results of the study provided insights into the pull-out failure mechanisms of screw connections in battens and enabled the development of suitable design rules for combined wind action and sub-zero temperature conditions. The findings of this study are expected to be of significant value to engineers and building designers who are involved in the construction of lightweight cold-formed steel buildings.
•Investigated the safety of external steel cladding systems under wind and blizzard conditions.•Conducted a detailed experimental study on the pull-out failures in thin steel cladding systems at sub-zero temperatures.•Identified the critical parameters that influence the pull-out failure capacities of batten screw connections.•Demonstrated the inadequacy of current pull-out design equations in cold-formed steel design standards.•Developed new pull-out capacity equations for the design of batten screw connections at sub-zero temperatures.
•Developed finite element models of load bearing LSF walls under standard fire.•Validated models using 11 LSF wall fire tests with various configurations.•Models included thermal bowing, local ...buckling and neutral axis shift of wall studs.•Provided useful load ratio versus time curves to predict fire rating of LSF walls.•Confirmed the superior fire performance of externally insulated wall panels.
Light Gauge Steel Framing (LSF) walls are made of cold-formed, thin-walled steel lipped channel studs with plasterboard linings on both sides. However, these thin-walled steel sections heat up quickly and lose their strength under fire conditions despite the protection provided by plasterboards. A new composite wall panel was recently proposed to improve the fire resistance rating of LSF walls, where an insulation layer was used externally between the plasterboards on both sides of the wall frame instead of using it in the cavity. A research study using both fire tests and numerical studies was undertaken to investigate the structural and thermal behaviour of load bearing LSF walls made of both conventional and the new composite panels under standard fire conditions and to determine their fire resistance rating. This paper presents the details of finite element models of LSF wall studs developed to simulate the structural performance of LSF wall panels under standard fire conditions. Finite element analyses were conducted under both steady and transient state conditions using the time–temperature profiles measured during the fire tests. The developed models were validated using the fire test results of 11 LSF wall panels with various plasterboard/insulation configurations and load ratios. They were able to predict the fire resistance rating within 5min. The use of accurate numerical models allowed the inclusion of various complex structural and thermal effects such as local buckling, thermal bowing and neutral axis shift that occurred in thin-walled steel studs under non-uniform elevated temperature conditions. Finite element analyses also demonstrated the improvements offered by the new composite panel system over the conventional cavity insulated system.
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