Structural behaviour of pre-fabricated composite pad footing foundation using cold-formed steel of lipped channel sections

Abstract

Pad footing foundations are traditionally made of concrete reinforced by high tensile steel bars moulded by timber formwork. This type of fabrication has three main disadvantages, which are large deviation of intended geometry due to weak structural integrity of used timber formworks, wastage of timber material as temporary timber formwork does not contribute to the strength of pad footing and as to be disposed after a certain number of usage, and longer construction time due to the need to remove the timber formwork after the concrete has hardened. Due to these disadvantages, the traditional method of constructing pad footing can cause an increase in construction cost and time, uncertainty in the quality of the final product and also environmental issues from the disposal of used timber formwork. To overcome the existing flaws of pad footing construction, the concept of pre-fabrication construction of pad footing foundation has been introduced using cold-formed steel lipped channel sections to replace timber as permanent formwork, and to replace high tensile steel bars as reinforcement in the pad footing foundation. However, such practice of using cold-formed steels in pre-fabricated pad footing foundation is still uncommon and no design guide has been established yet. This thesis investigates the moment and shear resistances and the failure modes of such pre-fabricated pad footing foundation designed to BS EN 1992-1. A total of 9 specimens were tested, which consisted of six 1000 mm x 1000 mm x 150 mm footings, and three 1000 mm x 1750 mm x 150 mm footings. The experimental result and theoretical calculation was on good agreement and the use of cold-formed steel increased the structural resistance of the footing due to composite effects. As a result, the proposed pre-fabricated pad footing foundation using cold-formed steel lipped channel sections is proved to be feasible in actual construction practice and can be reliably designed by using the existing code in BS EN 1992-1.