The rapid growth of modular construction has increased the demand for accurate and computationally efficient methods for predicting the shear performance of cold-formed steel members. Modular construction-optimised beams, characterised by a mono-symmetric triangular hollow flange geometry, exhibit shear behaviour that is not well represented by existing analytical formulations. This study proposes an explainable machine learning framework to predict the ultimate shear capacity of cold-formed steel modular construction-optimised beams using a validated finite-element dataset comprising 105 parametric models. Six supervised machine learning algorithms are trained and evaluated using resampling-based validation and statistical performance metrics. Categorical boosting achieved the best predictive performance, with a coefficient of determination of 95.9% and a mean absolute percentage error of 6.49% under 50 repeated train and test splits. Model transparency is supported using Shapley Additive Explanations, which confirm thickness and yield strength as the most influential inputs within the investigated domain. In addition, prediction uncertainty was quantified using empirical 95% prediction intervals, and the modelling workflow was strengthened by explicitly defining reproducibility and no-leakage conditions. Overall, the proposed framework provides an efficient and interpretable finite element surrogate tool for rapid design-oriented estimation of modular construction-optimised beam shear capacity within the defined parameter ranges and loading configuration.

This study presents a comprehensive numerical investigation into the combined bending–shear behaviour of hollow-flanged cold-formed steel (HFCFS) beams filled with lightweight concrete (LWC). Although previous research has independently examined the pure bending and pure shear responses of these composite members, their structural performance under simultaneous bending and shear remains unexplored. In this work, advanced three-dimensional finite element (FE) models were developed in ABAQUS to simulate the nonlinear behaviour of LWC-filled HFCFS beams subjected to various shear-span ratios. The modelling approach was validated using published experimental data and extended through a systematic parametric study that considered three beam geometries, two steel yield strengths (350 MPa and 450 MPa), two lightweight-concrete strengths (30 MPa and 50 MPa), and aspect ratios ranging from 1.5 to 3.5. The results demonstrated a clear progression of governing failure modes, from web shear buckling at low aspect ratios to combined shear–flexure interaction at intermediate spans and flexural-dominated failure at larger spans. Normalised shear and bending demand–capacity ratios (V/Vu and M/Mu) were used to identify the dominant limit state, revealing a predictable transition from shear-controlled to flexure-controlled behaviour. The findings enhance the understanding of composite thin-walled steel–concrete systems under combined actions and highlight the need for dedicated design rules for CF-HFCFS beams operating within the bending–shear interaction domain.

Purpose: Load-bearing fire rating is essential for maintaining the structural integrity of light steel frame (LSF) walls during fire events. While most studies examine single-sided fire exposure, two-sided exposure, relevant in some internal wall scenarios, remains underexplored. This study investigates the impact of both side fire exposure on the load-bearing fire rating of LSF walls under various fire conditions. Design/methodology/approach: This research employs finite element modelling (FEM) to simulate the structural and thermal response of LSF walls under two-sided fire exposure. The models were calibrated and validated using experimental data from previous studies to ensure accuracy. Parametric studies were conducted to evaluate the effects of plasterboard thickness, number of layers, cavity insulation and load ratios under varying fire scenarios including standard, prolonged, rapid and hydrocarbon fires. Findings: The results reveal that two-sided fire exposure significantly reduces the load-bearing fire rating of LSF walls compared to single-sided exposure. Under rapid and hydrocarbon fire conditions, the fire rating was reduced by up to 72%. Conversely, standard and prolonged fires resulted in lower reductions. The degradation in performance varies with construction configuration and exposure type, indicating that certain wall assemblies are more vulnerable under both side fire exposure. Originality/value: This study provides the first comprehensive computational investigation into LSF wall performance under two-sided fire conditions. The findings highlight critical gaps in current design practices, emphasizing the need for revised fire safety assessments for internal walls potentially exposed to both side fire scenarios. Designers and engineers can use these insights to improve fire resistance strategies in buildings using LSF systems.

Reinforced concrete structures in wastewater treatment plants (WWTPs) operate under uniquely aggressive conditions, including biogenic sulphuric acid attack, sustained moisture, elevated temperatures, and partial submergence. Although Fiber Reinforced Polymer (FRP) strengthening is well established for bridges and other concrete infrastructure, its application within WWTPs raises concerns regarding bond durability and long-term performance, and field case studies in such environments remain scarce. This paper presents the structural assessment and Carbon Fiber Reinforced Polymer (CFRP) rehabilitation of an industrial WWTP equalisation tank in Sri Lanka, in which a defective construction joint within an interior column had triggered progressive deterioration after 15 years of service, producing slab deflections of over 250 mm (span/32) far exceeding the BS 8110 serviceability limit of span/250. A multistage investigation combining visual crack survey, scanning electron microscopy (SEM-EDX), and three-dimensional finite element analysis identified two coexisting deterioration mechanisms: wastewater ingress through the defective joint, causing reinforcement corrosion and column fracture; and biogenic sulphuric acid attack within the tank headspace, producing ettringite formation in the slab and beam soffits. Rehabilitation was carried out under operational constraints, comprising column reconstruction, epoxy crack injection, externally bonded CFRP strengthening with elevated temperature post curing at 55–65°C to enhance the cured adhesive Tg, and protective finishing. An environmental reduction factor of 0.80, supported by accelerated ageing and lap shear bond data, was adopted in the strengthening design. Post rehabilitation analysis confirmed restoration of the vertical load path, reduction of peak bending moments, and re-establishment of structural continuity. The paper provides a complete diagnostic to rehabilitation workflow and practical guidance on material selection, surface preparation, post curing, and protective detailing for FRP applications in confined and chemically aggressive service environments.