Mahen Mahendran

Crest-fixed trapezoidal cold-formed steel (CFS) cladding systems, widely used in Australia and neighbouring countries, are prone to localized pull-through failures around screw fasteners under high wind uplift/suction loading. Unlike corrugated cladding, which exhibits localized dimpling-type failures, and trapezoidal cladding with wide pans, which often fails through transverse splitting, trapezoidal cladding with closely spaced ribs can experience either localized dimpling or splitting-type pull-through failures. These failures result from significant stress concentrations beneath screw heads and the limited ductility of high-strength steel, posing challenges for accurate prediction through analytical methods. As a result, the design of crest-fixed trapezoidal cladding with closely spaced ribs relies on experimental testing, with few design guidelines available to address these specific failure modes and pull-through capacity. This study proposes and calibrates a ductile damage material model specifically for very thin, high-strength cold-formed steel, enabling accurate simulation of damage initiation, progression, and fracture. The model was implemented in an advanced finite element framework capable of reproducing both localized dimpling and transverse splitting pull-through failures under static wind uplift loading. Validation against experimental data showed excellent accuracy with a low coefficient of variation of 0.02, while an extensive parametric study identified the effects of key parameters such as crest height that increased the capacity by up to 90%. The findings improve the understanding of pull-through behaviour and lead to practical design recommendations for optimising crest-fixed trapezoidal cladding systems. The proposed equation predicted the capacities within 5%, demonstrating strong potential for design-code adoption.

Purpose: This paper investigates the influence of using a lightweight aggregate called “Diatomite” in hollow masonry (i.e. cement) blocks for bushfire resistance. Design/methodology/approach: One of the 100-block series category (i.e. 90 mm thick) hollow masonry blocks were fabricated using a diatomite fine aggregate-based cement mix (i.e. cement-sand-diatomite mix). Properties of the mixed ingredients were determined, and the cement-sand-diatomite mix were developed based on the absolute volume method. After 28 days of curing, tests were conducted on hollow blocks, including density, compressive strength, bushfire and building fire resistance, and the results were compared with those of the cement-sand (standard) mix hollow block and one of the commercially available hollow blocks. Findings: The newly developed diatomite mix hollow block satisfies the density requirement for ultra-lightweight masonry units and the strength requirement for loadbearing hollow masonry units. It is the only block that complied with the temperature limit for unguarded interior surfaces of bushfire shelters and showed one-hour additional building fire resistance (−/120/120) than that of cement-sand mix (−/60/60) and commercial hollow blocks (−/60/60). Practical implications: The diatomite mix hollow block developed in this research can be suggested as a suitable loadbearing lightweight hollow masonry block for bushfire shelters and external walls of the buildings in bushfire-prone areas. Originality/value: Limited studies are available for hollow masonry blocks in relation to their bushfire and building fire resistance.

Thermal bridging through cold-formed steel (CFS) studs significantly reduces the thermal performance of light gauge steel frame (LSF) wall systems, particularly in climates demanding higher thermal resistance (R-value). While thermal breaks are commonly used, they increase material costs and construction complexity. According to NCC 2022, the minimum total R-value requirement for external walls ranges between 2.8 and 3.8 m²·K/W depending on the climate zone and building class. This study therefore evaluated web-perforated steel studs as a passive strategy to enhance thermal resistance of LSF walls, analysing 120 configurations with validated 3D finite element models in Abaqus and benchmarking in THERM. The results showed that web perforations consistently improved R-values by 14 to 20%, as isotherm contours and heat flux vectors demonstrated disruption of direct heat flow through the stud, thereby mitigating thermal bridging. Although the axial compression capacity of web-perforated CFS studs decreased by 29.5%, the use of 4 mm hole-edge stiffeners restored 96.8% of the original capacity. The modified NZS 4214:2006 and ASHRAE Modified Zone methods, incorporating steel area reduction and heat flux redistribution, closely matched Abaqus predictions, with coefficients of variation (COV) below 0.009, corresponding to less than 1% relative deviation between analytical and numerical R-values. Furthermore, application of web-perforated CFS studs in five external wall systems demonstrated improved thermal resistance, ensuring compliance with NCC 2022 R-value requirements across all Australian climate zones. Overall, the findings establish web-perforated studs as an effective solution for improving the energy performance of LSF building envelopes.