This study develops a validated finite element (FE) model for T-stub connections with Howick Rivet Connectors (HRCs) and carries out a systematic parametric analysis considering variations in rivet diameter, plate thickness, and steel grade. Using numerical simulations together with previously published experimental data, the accuracy of existing bearing and shear strength formulas is evaluated, revealing substantial discrepancies when these formulas are applied to a wider dataset. To address these limitations, new strength formulas are proposed and validated through reliability analysis, achieving an average test/FEA-to-predicted ratio of 1.04 and correctly identifying failure modes in 91% of cases. Compared with existing design formulas, the proposed equations reduce prediction bias by approximately 18% and decrease strength dispersion by about 5%, demonstrating notable improvements in both accuracy and reliability. Based on the combined numerical and experimental findings, design recommendations are provided to support the practical use of HRC connections in cold-formed steel structures.

Cold-formed steel (CFS) bolted joints formed with back-to-back channel sections are widely used in portal frame construction due to their efficiency and ease of fabrication. However, the discrete force transfer between individual channels produces non-uniform stress distributions within the joint region, leading to localised stress concentrations, shear lag effects, bimoment-induced stresses due to restrained warping, and premature web buckling. These effects can reduce the moment capacity of typical joints by up to 40% compared with the nominal capacity of the connected members; however, this reduction is not explicitly addressed in current CFS design standards, including AISI S100, AS/NZS 4600, and EN 1993–1–3, which treat member and joint capacities independently. To address this gap, this paper presents a comprehensive experimental and parametric investigation to quantify the capacity reduction in CFS bolted joints and provide a reliable design method for practical applications. A detailed finite element (FE) model was first developed and validated against experimental results from CFS portal frame joint tests. Subsequently, an extensive parametric study comprising over 3400 FE simulations was performed to capture the influence of cross-sectional non-dimensional slenderness, as well as a wide range of geometric, material, and joint parameters. Based on these findings, a simplified design equation is proposed to enable reliable prediction of the reduced moment capacity of back-to-back channel bolted joints. The application of the proposed design equation is then verified against both numerical and experimental results of CFS frames, demonstrating excellent accuracy, with predictions within 1–3% of the actual capacities on average and coefficients of variation ranging from 0.06 to 0.09.

Cold-formed steel (CFS) structural members are widely used in residential construction due to their favourable properties and advances in manufacturing. To improve thermal performance, slits are often introduced into the webs of these members. However, this alteration can compromise their axial strength. Although this has important structural implications, few studies have quantified the effect of slits on axial capacity, particularly under eccentric loading conditions. The authors previously examined slitted CFS sections under concentric axial compression and through this research address that gap by conducting a comprehensive parametric study on CFS studs with slits, subjected to combined axial compression and minor axis bending through eccentric loading. A total of 1134 finite element analysis (FEA) models were created, varying parameters such as member length, thickness, cross-sectional dimensions, and six different load eccentricities. These models evaluated how slits influence axial capacity when minor-axis bending occurs due to eccentric loads. The FEA results were compared with predictions from the general interaction equation provided in the Australian/New Zealand Standard AS/ NZS 4600. On average, the design equations underestimated the strengths by approximately 13% for eccentricities ranging from 10 mm to 25 mm, while they overestimated the strengths by about 20% for 50 mm eccentricities. Based on these findings, a new design interaction equation was developed, incorporating element and web slenderness ratios. A reliability analysis within the AISI-S100 framework confirmed that the proposed design modifications satisfy required safety standards.

The use of aluminium for roof claddings provides a durable alternative to cold-formed steel (CFS). However, these claddings can experience localised pull-through failure at the connections under wind uplift. Currently, no design guidelines exist for predicting the pull-through capacity of trapezoidal aluminium roof claddings. This study investigates the pull-through failure behaviour of trapezoidal aluminium roof claddings with wide pans and closely spaced ribs under static wind uplift. A finite element (FE) model was developed and validated against existing CFS trapezoidal cladding experimental tests under static wind uplift, with additional validation for representing the behaviour of aluminium as a material. Further, a comprehensive parametric study involving 698 FE models was conducted by varying material properties, thickness, geometry, cladding span, and screw head/washer diameter. The comparison of the parametric study results with predictions from existing aluminium design guidelines (Aluminium Design Manual (ADM 2020), Australia and New Zealand Standard (AS/NZS 1664), and Eurocode (EN 1999-1-4)) revealed that the design equations in these guidelines were inaccurate for predicting the pull-through capacity of trapezoidal aluminium claddings. Therefore, simplified design equations were developed to determine the pull-through capacity of trapezoidal aluminium claddings. Finally, a reliability analysis confirmed the high reliability of these proposed design equations.

This paper proposes the use of cross-laminated timber (CLT) panels in conjunction with back-to-back cold-formed steel (CFS) channel or angle sections in combination with laminated veneer lumber (LVL) beam, for composite CFS-timber beams. Under a hogging and sagging moment, part of the CLT panel will act compositely with CFS-LVL in order to resist compression, while the lower part of CFS-LVL web will be in tension. Whilst shear lag effects have been well-researched for concrete-steel composite beams, there has been little research on this for CLT panels working with CFS-LVL sections. In this paper, the finite element method (FEM) is used to determine the effective flange width (FFW) for CFS-timber beams. In conclusion, the obtained result has shown that the EFW increases with any changes that lead to an increase in the ratio of the transverse layer’s depth to the longitudinal layer’s depth. Moreover, combinations of CFS sections with LVL have significantly resulted in the depth-of-beam decrease.

The use of cold-formed aluminium (CFA) channel sections in harsh environments could be a feasible alternative to cold-formed steel (CFS), where web holes are often provided in the beam member to accommodate electrical and plumbing services. When web depth is limited, elongated holes are preferred over circular ones, though they can considerably reduce flexural capacity. To mitigate this effect, stiffeners are often added around the hole edges. Currently there is very limited research available on the flexural behaviour of CFA channel sections with different types of web holes. This study investigates the moment capacity of CFA channels with various types of web openings, using experimentally validated finite element (FE) models. A comprehensive parametric study is conducted using 1168 FE models to investigate the effects of cross-section size, web hole shape and size, and stiffener length for four different cases: (i) elongated unstiffened, (ii) elongated stiffened, (iii) circular unstiffened, and (iv) circular stiffened CFA channel web holes. It is shown that the moment capacity of the sections considerably decreases as the web hole length-to-depth ratio (b/d) increases, with greater impact at higher hole diameter-to-depth ratios (a/d), on average by 14.3 % and 9.3 % for channels with unstiffened and stiffened web holes, respectively. The results also indicate that the current Direct Strength Method (DSM) design equations are conservative by 11 %, 9 %, 19 %, and 13 % for unstiffened elongated, stiffened elongated, unstiffened circular, and stiffened circular web holes, respectively. As a result, two sets of new DSM-based design equations are proposed for each scenario to predict local buckling and distortional/local-distortional buckling of CFA channel with web holes. Finally, the robustness of these equations is confirmed through reliability analysis, with a reliability index greater than 2.5 for all cases.

Cold-formed steel (CFS) built-up box sections often exhibit axial strengths greater than the sum of their individual components. Since truss members primarily carry axial forces, they are well-suited for replacement with such sections. Incorporating high-performance Howick Rivet Connectors (HRCs) enables these built-up members to substantially improve the load-bearing performance of truss systems. However, related studies remain limited. This study addresses this gap by investigating the structural performance and design methodology of such trusses for potential applications in modular construction. A comparative experimental program, involving 64 specimens, was conducted to evaluate the axial capacity and failure behavior of built-up columns with HRCs versus conventional screw fasteners. Finite element models were developed and validated against experimental results, enabling a parametric study of trusses with built-up chord and diagonal members. Among the truss configurations investigated, replacing only the chord members with built-up sections achieved the highest ratio of serviceability limit strength to self-weight and demonstrated the most structurally efficient performance. A practical design method was subsequently proposed to enhance the accuracy of truss strength predictions by accounting for the effects of eccentric compressive loading in the chord members.

Cold-formed steel (CFS) portal frames, typically consisting of back-to-back channel sections with bolted eaves and apex joints formed through brackets, are commonly used in industrial, agricultural, and commercial buildings in New Zealand and Australasia. In design practice, their design is often simplified by assuming rigid joints, which can underestimate frame deflections by a factor of two (or more), and underestimate the bending moment at the apex by as much as 40 %. Furthermore, particularly for column design, shear lag effects at the eaves are ignored, overestimating strength by around 20 % to 40 %. A combination of these simplifications by practicing engineers can lead to premature failures in the connection zones and potentially result in unsafe design outcomes. This paper presents, for the first time, a simple beam idealization method that engineers can use to predict frame capacity. A detailed non-linear finite element (FE) model of a CFS portal frame is developed and validated against experimental results. Using the validated FE model, the ultimate failure load of a frame can be predicted (assuming that the brackets do not fail first). The validated FE model is then used to assess the influence of joint flexibility, moment capacities of the eaves and apex brackets, and the reduced moment capacity of the channel section due to the shear lag effect in the eaves joints. Based on these findings, the accuracy of the simplified design method is assessed. The simplified approach predicts the load capacity of CFS portal frames within 1 % of detailed FE models.

This paper presents an experimental and numerical investigation into the behaviour of cold-formed steel (CFS) lipped channel sections with plain webs, unstiffened circular web openings, and edge-stiffened circular web openings subjected to combined bending and shear. A total of 24 laboratory tests and 378 validated nonlinear finite element (FE) models were used to quantify the effects of shear-span ratio, opening ratio, web slenderness, and stiffener geometry on strength and failure modes. The results show that the shear-span ratio governs the global response, controlling the transition from shear-dominated behaviour to bending-shear interaction, while web openings significantly reduce capacity under shear-dominated conditions by disrupting the diagonal load path and promoting local buckling. Edge stiffeners enhance local stability and partially restore strength, particularly for large openings and short shear spans, although their influence diminishes as global behaviour becomes dominant. Comparisons with AISI S100 indicate that the current interaction equation is conservative for plain-web sections, underestimating capacity by approximately 16%, and that it does not account for web openings. New design equations based on reduction factors are proposed for sections with unstiffened and edge-stiffened openings, with the functional form reflecting the interaction between opening-induced local instability and global bending-shear behaviour. The proposed equations are shown to satisfy target reliability requirements and provide a practical basis for the design of perforated CFS members under combined bending and shear.

Warping restraints at the supports of cold-formed steel (CFS) columns restrict longitudinal flange displacements during distortional buckling, leading to enhanced column strength. Current design guidelines, however, do not account for this effect, potentially underestimating the structural capacity. The paper addresses this gap by providing a deeper understanding of the behaviour and proposing new design approaches for practical applications. The Direct Strength Method (DSM) is employed using two complementary approaches for determining elastic critical distortional buckling loads: (i) the Finite Strip Method (FSM), which assumes free warping, and (ii) Finite Element (FE) eigenvalue buckling analysis incorporating restrained warping at the ends. A comprehensive parametric study is performed on CFS channel columns with varying lengths, thicknesses, and cross-sectional geometries, as well as the inclusion of edge stiffeners and intermediate web stiffeners. The results show that restraining distortional warping can significantly impact the distortional buckling strength, by up to 45%, particularly for short columns with cross-sections featuring both edge and intermediate web stiffeners. In addition, the use of the standard DSM assuming free warping results in an average underestimation of approximately 27% in predicting the strength of CFS channels with edge and intermediate web stiffeners. Based on these findings, new DSM-based design equations are proposed to account for the effects of restrained distortional warping in CFS columns. Finally, a reliability analysis is conducted within the AISI framework on a dataset, including the results of proposed design equations and experimentally validated FE models, to ensure the required safety level.

Self-drilling wing screws are commonly used in hardwood and composite board applications and offer a promising alternative to traditional bolts for connecting thick hot-rolled high-strength steel to timber in Australia and New Zealand because timber cracking is avoided during installation. Despite this potential, the shear behaviour of self-drilling wing screw connections in structural steel-timber systems has not yet been investigated. This study investigates the shear performance and load-carrying capacity of self-drilling wing screw connections between radiata pine timber and hot-rolled steel plates through an extensive experimental programme. Material characterisation included tensile coupon tests, screw bending tests, moisture content measurements, screw pull-out tests, and screw embedment tests to determine the mechanical properties of the steel, timber, and screws. A total of 70 connection tests were conducted with varying steel thickness (8-20 mm), timber thickness (15-45 mm), number of screws (1-3), and screw axis angle (45 degrees-90 degrees). The effects on load capacity, initial stiffness, and ductility were evaluated. Increasing the steel plate thickness from 8 mm to 15 mm increased the average shear capacity by approximately 25%, whereas increasing the timber thickness from 15 mm to 45 mm increased the capacity by 17% for single-screw and 32% for double-screw configurations. Comparisons with Eurocode 5 (2024) show significant inconsistencies: in some cases the design predictions are up to 30% conservative, while in others they overestimate the capacity by as much as 50%. To address these discrepancies, modified design equations based on Johansen yield theory are proposed to predict the shear capacity of self-drilling wing screw steel-timber connections.

This study conducts experiments on Q345 cold-formed steel (CFS) screw connections at ambient and elevated temperatures; investigates the effects of the number of screws, arrangement, and loading system on the mechanical properties; and investigates the load transfer and group effects in multiple screw connections. The results reveal that below 400 degrees C, the main failure mode of multiple screw connections is screw tension-shear failure, whereas above 400 degrees C, it shifts to screw tilting accompanied by hole wall pressure failure. The arrangement of the screws and cyclic tensile actions had minimal effects on the ultimate load capacity of the multiple-screw connection. Under cyclic tensile action, both the unloading stiffness and the reloading stiffness increased with increasing number of screws but decreased with increasing temperature. With fewer than five screws, the group effect on the number of screw connections was insignificant, with the deviation between P (experimental value) and P2 (the limit load of a single-screw connection multiplied by the corresponding number of screws) remaining within 10 %. However, as the number of screws exceeded five, the group effect became more pronounced, leading to an increase in the deviation between P and P2. This deviation reached a relative value of 38 % with twelve screws. During the loading process, the central screws initially bore the primary load before being redistributed to the end screws. The load-carrying capacity of the end screws usually first increases. Prediction models for the ultimate load and load-displacement curves of screw connections at ambient and elevated temperatures were developed.

This study investigates experimentally and analytically the performance of a new Three-Dimensional Seismic Isolator (3DSI) designed to control the horizontal-vertical coupled responses of multi-story buildings. The proposed isolator system adopts the concept of Super-High-Damping-Rubber (SHDR) to achieve vertical isolation by decreasing the vertical effective stiffness and increasing the vertical effective damping, thus minimizing the imparted vertical acceleration into the superstructure. Three different case-study buildings, including dual 5-story steel frames with Fixed Base, Conventional Seismic Isolators (CSI), and the proposed 3DSI, were analysed using OpenSees software based on experimentally validated models under a set of 12 earthquake records. The vertical period of the isolator system was tuned to reach 0.3 s, at which most of the vertical ground motions are degraded to less than 2.0 g. The results indicate that the proposed 3DSI system can considerably decrease the vertical and horizontal responses by up to 65% and 20%, respectively, compared to the CSI system. It is shown that using the 3DSI system minimizes the potential damage by reducing the magnitude of the vertical responses, while it also leads to smaller compression and tension axial loads and less inter-story drifts. In contrast, Fixed Base and CSI buildings experienced significantly escalated vertical accelerations, particularly on long-span beams, potentially leading to extensive non-structural damage during strong earthquake events.

Cold-formed steel (CFS) channel sections are regularly used as floor joists, and such sections are vulnerable to web crippling, especially as span lengths increase, leading to potential failure under combined web crippling and bending. Over the past decade, the industry in New Zealand has developed CFS channel sections with circular edge-stiffened web holes. However, no experimental tests or numerical studies for these channel sections when subject to combined web-crippling and bending have been reported in the literature. This paper presents a numerical investigation using non-linear finite element analysis (FEA) to study the combined web crippling and bending behaviour of these CFS channel sections that have not only edge-stiffened web holes but also unstiffened holes. Validated FEA models enabled a parametric study on CFS channel sections, encompassing 2268 FEA results. Those FEA results were compared with the interaction equations in three CFS design standards. Moreover, the effectiveness of design equations presented in the literature was also evaluated. New design equations with the form of combined web crippling-bending strength reduction factors (R-p) are proposed. Finally, a reliability analysis was conducted to ensure the proposed equations are accurate in predicting the combined web crippling-bending strength of CFS channel sections with unstiffened and edged-stiffened circular web holes.

This study presents a novel application of explainable machine learning techniques to investigate the web crippling behaviour of Cold-Formed Steel (CFS) lipped channel beams under Interior-Two-Flange (ITF) loading condition. Three Machine Learning (ML) models, including Extreme Gradient Boosting (XGB), Random Forests (RF), and Artificial Neural Networks (ANNs) were developed to predict web crippling capacity under ITF loading. Considering a wide range of geometries for CFS lipped channels, a dataset of 400 instances was generated through validated numerical modelling to train and test ML models. All models demonstrated high reliability, exceeding the target reliability index of 2.5. Among these, XGB outperformed other models, achieving an R2 score of 0.996 on the testing data. The predictive performance of the XGB model was further evaluated using 33 unseen experimental data points collected from the literature and compared with existing design formulas for web crippling capacity. XGB demonstrated superior accuracy, achieving the lowest error of 6.87 %. Shapley Additive Explanations (SHAP) were employed to elucidate the influence of geometric parameters on web crippling strength. The SHAP-based interpretations aligned with established domain knowledge, confirming the validity of the findings. This study presents a time-efficient, accurate, and interpretable approach to predicting web crippling strength, offering a valuable complementary approach for the design of CFS lipped channel sections.

Roof cladding, a vital component of any structure, is fabricated from material that is durable, affordable, and weatherproof. Metal roof claddings, known for their lightweight nature, durability, cost-effectiveness in construction and maintenance, and impressive strength-to-weight ratio, have been widely adopted worldwide. However, despite these advantages, metal roof claddings are particularly prone to failure during extreme wind events, such as storms, cyclones, and hurricanes. The two primary categories of metal roof claddings are long-run profiles and tray profiles. This study conducts a comprehensive review of research focused on standards used for quantifying wind loadings on roof structures, as well as the wind resistance capacity of various profiles of metal roof claddings under wind uplift loading. The review encompasses both experimental and numerical studies, exploring test methods, numerical modeling techniques, and modes of failures associated with different roof cladding profiles under wind uplift loading conditions. Additionally, the paper examines studies related to fragility and vulnerability analysis, along with risk assessment, pertaining to metal roof claddings. In conclusion, the paper offers critical remarks and provides recommendations for future work based on identified research gaps. The aim is to guide future studies in addressing challenges related to the wind performance of metal roof claddings and contribute to the development of more resilient and secure roofing systems.

Cold-formed steel (CFS) channel sections with web openings are widely used to accommodate services in light-frame construction. However, their structural performance under combined axial compression and bending, particularly when openings are either unstiffened or edge-stiffened, remains poorly understood. This study develops a validated nonlinear finite element model that accounts for material nonlinearity and initial imperfections to assess the behaviour of such sections under eccentric loading. A comprehensive parametric study involving 3078 simulations was conducted to quantify the effects of slenderness, width-to-thickness ratio, hole configuration (number, size, location), stiffener ratio, and eccentricity about both principal axes. Results show that unstiffened web holes can increase the axial-bending interaction ratio by up to 60 % beyond the limits of AISI S100 and AS/NZS 4600, while edge stiffeners effectively limit this increase and improve capacity by 15 % on average. The detrimental effects of unstiffened holes diminish with increasing eccentricity and become negligible beyond specific eccentricity thresholds. Based on the simulation results, new design equations are proposed to account for geometric and loading parameters explicitly. These equations reduce prediction error by 20 % and address key conservatism and non-conservatism issues in current design standards, offering a pathway toward safer and more economical CFS member design.

In this research, a comprehensive study was conducted involving 85 specimens to investigate the axial capacity of cold-formed steel (CFS) studs with swaged sections. The study included 15 tests and 70 finite element analyses. To replicate real-world conditions accurately, self-drilling screws were used to connect the noggin and tracks to these studs. The specimens included tests with and without a noggin for comparative purposes. The study found that although having a swaged section in the middle of a stud slightly decreases the axial capacity, the presence of a noggin compensates for this reduction and even increases its axial capacity by 15.5 %. Finite element models, considering material nonlinearity and geometric imperfections, were validated against these test results. Parametric studies explored how variations in swaged section cross-section dimensions affect axial loads. Results indicated that web stiffeners with lengths between 0.6 and 0.8 times the web depth lead to higher axial loads, recommending this range for swaged section design in CFS studs. Comparing experimental test results (PEXP) with design strengths (PDSM) from the Direct Strength Method, the average PEXP/PDSM ratio was found to be 1.06, with a coefficient of variation of 0.07. The findings provide practical guidance for the design of CFS framing systems, particularly in prefabricated and modular construction, where swaged sections are widely used to enhance assembly efficiency.

This study introduced a novel approach to derive a design equation using Machine Learning (ML) to estimate the shear strength of Cold-Formed Steel (CFS) Rectangular Hollow Flange Beams (RHFBs) with unstiffened and edgestiffened circular openings in web. Based on experimental data, a comprehensive series of numerical modelling was conducted to develop data for ML models. Machine learning models, namely, (a) Extreme Gradient Boost (b) Light Gradient Boosting Machine (c) Random Forest and (d) Support Vector Regressor were trained and validated using the data obtained from parametric numerical models. The XGB model showed the best predictive accuracy for shear strength. Additionally, Shapley Additive Explanations (SHAP) were used to interpret the model predictions. The developed ML models showcased better accuracy compared to the existing semi-empirical equations. As a novel complementary approach, this study developed a simplified equation for the first time using XGB and Shapley values to estimate the shear strength reduction factor of doubly symmetric RHFBs with both edge-stiffened and unstiffened circular openings. The proposed equation obtained a reliability index (beta) of 2.78 and outperformed the existing semi-empirical formulations, resulting in an improved design formula for RHFBs.