Development of innovative modular construction beams

Kanthasamy, Elilarasi (2024) Development of innovative modular construction beams. Doctoral thesis, Northumbria University.

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Abstract

Modular construction is certainly an emerging revolution in this century, where the UK and many developed nations have set several sustainability-related targets including net zero carbon emission. However, Modular Building System (MBS) faces challenges in enhancing sustainability while improving its structural performance. The application of cold-formed steel (CFS) has become more popular in recent years due to its inherent benefits which offer high strength-to-weight ratio, high recyclability rate, lower embodied carbon, and lightweight. Prefabrication of CFS to the specific demands often leads to novel CFS sections and thus achieves the structural requirements of the current construction industry. This thesis aims to investigate numerous ideas such as novel beam profiles containing hollow flanges and web stiffeners, optimised beam profiles, high-strength materials, diverse CF materials, and built-up open and closed sections to come up with innovative beam profiles and impressive recommendations for MBS. The outcomes will demonstrate elements with enhanced structural performances and recommendations for the building industry to achieve sustainability goals.

A wider range of CFS sections have been tailored and are in application currently in the building industry to meet the structural as well as other requirements, Modular Construction Optimised (MCO) beam and SupaCee beam are among them. MCO beam was introduced based on the ‘six-sigma’ approach and identified that MCO beams have potential structural advantages such as reducing the weight of floor joists by 18% compared to built-up Rectangular Hollow Sections (RHS). The section moment capacity of MCO increases by up to 25% compared to the Lipped Channel Beam (LCB) for the same amount of material. Also, it is declared that higher web-flange juncture fixity (90%) would lead MCO beams to behave better under shear conditions due to increased Stiffness and better load distribution which. Web crippling strength investigation of MCO revealed that around 30 % to 50 % increment can be obtained by MCO compared to similar LCB sections. SupaCee sections are another novel section that contains web stiffeners and curved lips making them extremely strong. The structural performances of the SupaCee section indicated that the SupaCee sections perform well compared to the LCBs when undergoing shear and bending. Enhancement in bending capacity of the SupaCee section varies from around 13 % to 90 % whilst comparisons indicated almost 3 % to 30 % shear capacity increment in the SupaCee section. The modified equations were proposed along with the structural investigations of the MCO and SupaCee sections. The results and proposed equations may be referred to for the application of MCO and SupaCee sections in the industry.

The conventional building industry and MBS demand long and tall structures that are considered cost-effective and environmentally friendly elements. Built-up sections are capable of bearing high structural loadings and are applicable for larger spans. Hence, the buckling behaviour of open and closed built-up sections was studied whilst the effect of different screw arrangements as well as screw spacings was also carefully investigated. The increment in section moment capacity of the built-up section was more than doubled for open and closed sections. A maximum of up to 156% increment was observed for the built-up sections compared its single sections for the selected parametric study. The optimised profiles were extracted from the literature and section moment capacities of open built-up beams were further investigated which performed well under local buckling failure. The outcome can be considered for efficient structural components in MBS.

The construction industry is still required for various aspects for its betterment. CFS with high-strength materials are greater in strength and toughness. CFS is vulnerable to web crippling compared to other structural failure due to the nature of thin-wall elements. Therefore, the web crippling behaviour of CFS using high-strength materials was also investigated to adopt them in the applications. Also, accommodation of service integrations in buildings is used to adopt in the CFS sections using openings in the web area, which practice came up with effective utilization of floor space and optimised floor height. Even though web opening adversely affects the structural performances of CFS, a few recommendations such as edge-stiffened openings are introduced. Therefore, an investigation on stiffened openings also was carried out to provide recommendations.

Diverse cold-formed materials such as CFS, Cold-Formed Aluminium (CFA), and Cold-Formed Stainless Steel (CFSS) can be applied in Engineering practice considering their structural performances to come up with cost-effective proposals. A few numbers of analyses were carried out to investigate their structural performance in terms of local buckling capacities. The conclusion has been drawn that CFSS performs well compared to CFS and CFA when considering similar material strength. However, detailed analyses of different CF materials should be carried out further to widen their structural applications.

There have been several research studies focused on investigating various aspects of MBS such as the structural, social, economic, and safety performances. However, there are still challenges for more efficient structural elements with sustainability aspects, demand for longer spans and minimized material usage to enhance their benefits in terms of environmental and economical (require for lightweight materials and more access space, transportation restrictions, improving structural, fire and energy performances). Therefore, innovative beam profiles, optimised beam profiles, high-strength materials, built-up open and closed sections, and various CF materials have been studied broadly. Overall outcomes and recommendations have been proposed in this thesis to attain the sustainability aspects along with enhanced structural performances of MBS. Also, a few innovative beam profiles have been proposed, ideal for efficient design solutions, identifying the UK’s housing crisis.

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