Mani Anbarasu

Traditional hot mix asphalt for pavements has a high carbon footprint, necessitating cleaner alternatives like cold mix asphalt (CMA) with strong mechanical performance. Cementitious fillers improve CMA properties, while waste steel shavings further enhance them for more durable pavements. Accordingly, this study was aimed at exploring the influence of waste steel shavings on the mechanical response of the compacted CMA. The fine aggregate was replaced by waste steel shavings in five variations ranging from 10% to 50% by weight of the fine aggregate. The specimens were prepared in accordance with the requirements brought out for the Marshall Stability tests, given in American Specification ASTM D6927-06 (2015). The mix design conforming to Indian Standard IRC: SP-100 (2014) was adopted in the current study. Unreinforced specimens with no steel shavings were also prepared to serve as benchmark specimens for better interpretation of results. Three types of tests, namely, Marshall stability test, indirect tensile strength test and resilient modulus test, were carried out. Comparison of unreinforced and reinforced specimens revealed that incorporating waste steel shavings significantly improves CMA’s mechanical properties. The optimal fine aggregate replacement with shavings for maximum performance was identified as 30%.

Purpose: Tubular members are widely used in structural applications such as trusses, frames and lattice towers, where joints play a crucial role in transferring loads effectively. The purpose of this study is to evaluate the structural performance of cold-formed steel (CFS) T-joints with square tubular sections (STS) under combined axial compression and bending. By focusing on enhancements through side-plate reinforcement, the study examines the impact of reinforcement on joint strength, load capacity, stiffness and failure delay.Design/methodology/approach: The study involves experimental testing of six CFS T-joints with a brace-to-chord width ratio of unity, fabricated through automatic gas metal welding. To enhance load capacity, stiffness and delay joint failure, side plates of varying lengths were welded at the brace-chord junction. Performance indicators – maximum load, stiffness and deformation at failure – were analysed. A numerical analysis explored the influence of critical ratios, such as brace-to-chord width and thickness, on joint strength. Comparative assessments with Eurocode 3 (EC3) and CIDECT predictions highlighted inadequacies, leading to proposed amendments in CIDECT incorporating a reduction factor, validated through reliability analysis.Findings: Current predictions of joint strength by EC3 with and without considering the reduction factor, as well as CIDECT without considering the reduction factor, were found to be inadequate in accurately predicting the joint strength of CFS square tubular T-joints reinforced with side plates. Finally, this study proposes amendments to be incorporated into CIDECT, accounting for a reduction factor to enhance the accuracy of predicting T-joint strength. Furthermore, the reliability of these proposed changes was confirmed through rigorous reliability analysis.Originality/value: This study provides valuable insights into the behaviour of CFS T-joints with STS under combined axial compression and bending – an area with limited existing research. By incorporating side-plate reinforcements, the study demonstrates enhanced load capacity, stiffness and delayed failure in T-joints, offering a novel approach to improving joint performance. Additionally, it critically examines and identifies inadequacies in current strength prediction models (Eurocode 3 and CIDECT), proposing a modified CIDECT approach with a reduction factor for better accuracy. These findings offer valuable contributions to the design and application of reinforced CFS T-joints in structural engineering.

In recent years, there has been a compelling need to adopt cold‐formed ultra‐high‐strength steel (CFUSS) in the construction industry owing to its numerous advantages, such as a higher strength‐to‐weight ratio, flexibility in achieving desired shapes, and adaptability over longer spans. Among the various applications, CFUSS lipped channel sections are commonly used as purlins and joists in steel structural systems. However, these sections are susceptible to different failure modes, particularly web crippling, which presents significant challenges. Currently, the current design rules lack specific guidelines for estimating the web crippling capacity of CFUSS sections. To address this crucial gap, the present study focuses on a comprehensive numerical investigation of the web crippling response of CFUSS lipped channel sections under interior‐two‐flange (ITF) loading conditions. Finite element (FE) models were developed using the ABAQUS package, verified against published test data, and subsequently used in an extensive parametric study. The ultimate web crippling capacity obtained from the parametric study was used to evaluate the accuracy of the current design equations in various design standards. The findings revealed that the existing design equations inadequately predicted the ultimate web crippling capacity of CFUSS lipped channel sections subjected to the ITF loading condition. Consequently, a modified design equation is proposed, utilizing the same approach as the current design standards, and a new direct strength method (DSM) approach is developed and verified through reliability analysis. The proposed modified design equations offer promising solutions to ensure safer and more reliable design practices for CFUSS structures in the construction industry.

In the companion paper, test results were presented to explore the flexural performance of cold-formed ferritic stainless steel (FSS) closed built-up beams. Each specimen was fabricated by joining two lipped channels in a face-to-face configuration and securing them with spot welds at intermediate points along the beam span. Sectional aspect ratio, compression flange’s sectional slenderness and moment gradient were the key parameters varied to explore their influence on the flexural response of such members through tests. The current paper establishes a simplified finite element (FE) model of cold-formed FSS closed built-up beams and verifies it against the test results. Further, an extensive parametric study is carried out using the validated FE model to generate a large pool of data points. A wider database comprising of test results, numerical results obtained from this study and numerical results available in the companion paper were used to critically examine the adequacy of the current Australian Specifications (AS/NZ), American Standard (SEI/ASCE-8), European Code (EN 1993-1-4), Modified Eurocode approach suggested by Gardner and Theofanous, and Direct Strength Method (DSM) in North American Specification (AISI-S100: 2016), Modified DSM approach proposed by the authors in the literature and Continuous Strength Method (CSM) for cold-formed steel (CFS) flexural members. This makes the current study the first to extensively assess the accuracy of the various design guidelines available in the codes and other relevant literature, which explicitly highlighted their grave limitations. Accordingly, through suitable modifications and recommendations, new design rules are proposed to reliably and safely predict the flexural capacity of cold-formed FSS closed built-up beams.

High-performance steel has emerged as an advanced structural material in the construction practice of industrial buildings, due to its excellent properties. However, fire poses a significant threat to cold-formed steel structures, as they are prone to deform and buckle under the exposure, potentially leading to building collapse. This study aimed to evaluate the post-fire web-crippling behaviour of high performance CFS sections for End Two Flange (ETF) and Interior Two Flange (ITF) load cases. Two types of specimens were used: CFS webs without holes and CFS webs with circular holes. All test specimens were heated according to the ISO 834 standard fire curve and were subsequently cooled by air or water. A total of 52 specimens (ambient and post-fire) were tested under ETF and ITF load conditions. The load-deflection behaviour and failure modes were evaluated through experimental and numerical analysis. Finite element modelling was used to compare the load-deflection behaviour and failure modes of CFS members with experimental results. The experimental results indicate that the web load-carrying capacity of the high-performance steel member decreases drastically as the heating duration increases. Furthermore, the ITF load case specimens exhibited a lower strength loss than the ETF load case specimens at elevated temperatures. There was an excellent agreement between the experimental and FEM results in terms of the load-carrying capacity and failure modes of high performance CFS.