Optimum design of cold-formed steel beams for structural and modular building applications

Abstract

The construction industry focuses on more economical and efficient design solutions to address the present and future challenges. The challenges are the need for improved structural, fire, energy, acoustic performances, and other aspects in sustainability, climate change, and the need for emergency response infrastructures. The thin-walled Cold-Formed Steel (CFS) structural members uniquely produce effective design solutions due to their inherent advantages, including higher load-carrying capacity. CFS structural members are subjected to modifications to achieve enhanced structural, fire, energy, and other performances. These are achieved through optimisation studies, developing innovative profile shapes, and allowing staggered slotted perforations at the web segment. The current design guidelines for the CFS systems are not suitable to assess the performance of innovative profiles. Modular Building System (MBS) based construction method has been identified as an efficient construction method worldwide, especially in the UK. Most of the engineering works are performed off-site and leaving assembly of the pre-engineered modules on-site. This thesis aims to improve the overall performance of CFS beams through optimisation studies, considering innovative cross-sectional shapes and introducing staggered slotted perforations. The outcomes of the thesis would be value-added solutions to the steel-framed modular units in terms of improved structural, fire and other requirements.

The optimisation framework available in the literature for CFS members has prominently considered the bending response. Researchers have not considered other structural actions such as shear and web crippling. This study aims to optimise the CFS beams considering bending, shear, and web crippling actions. The optimisation was performed intending to (a)maximise the structural strength for a given amount of material and (b) minimise theamount of material for a given structural strength. The optimisation framework followed Eurocode 3 (CEN, 2006b, CEN, 2006a) provisions for structural capacity determination and, Particle Swarm Optimisation (PSO) and Wale Optimisation Algorithm (WOA) for optimisation. The optimised capacities were verified with non-linear Finite Element (FE) analyses. The results showed that 65% of bending capacity could be enhanced, and 24% of the material can be saved for the optimised sigma section compared to the reference section. An overall structural optimisation methodology taking all three actions into account was developed, and the results also demonstrated that bending capacity could be enhanced without harming the shear and web crippling capacities.

The development of thermo profile – CFS channels with staggered slotted perforations – has also enabled essential innovations in thermal efficiency as the perforations in staggered manner controls the thermal bridging across the profile. In order to effectively use it in MBS, the structural capacity and behaviour of CFS beams with staggered slotted perforations was investigated through FE models, which was successfully validated with experimental results. New strength reduction factor-based design equations were proposed through a wide range of parametric FE analyses and derived data pools of results. These enable engineers to consider new generations of CFS beams with staggered slotted perforations to enhance the thermal performance with the knowledge of reduction in structural capacity.

The performance of optimised CFS beams in the fire was studied by employing the optimised sections in conventional and modular floor panels. The investigation was performed through the heat transfer FE models validated with the fire test of floor panels designed with CFS beams. The results demonstrated that a modular floor panel could exhibit a substantial structural fire-resistant rating than a conventional floor panel due to its double skin nature. The results showed up to 75% enhancement in structural fire rating for the floor panels designed with optimised sigma sections.

To date, research on MBS focused on investigating the structural, social and economical, and safety performances and indicated that there are challenges (Need of lightweight materials and more access space, transportation restrictions, improving structural, fire and energy performances) associated with their use, yet to be addressed. Therefore, optimisation studies, staggered slotted perforations, and fire performance investigation findings were collectively studied to address these challenges. A conceptual design of MBS was developed, demonstrating the potential for lighter sustainable, and improved structural, fire, energy and healthcare performances. The proposed MBS is ideal for efficient design solutions, including emergencies like the present covid-19 situation.

Date of Award	21 Oct 2021
Original language	English
Awarding Institution	Northumbria University
Supervisor	Keerthan Poologanathan (Supervisor), Brabha Nagaratnam (Supervisor), Marco Corradi (Supervisor), Shanmuganathan Gunalan (Supervisor) & Konstantinos Daniel Tsavdaridis (Supervisor)