Behaviour and design of stainless steel and stainless steel-concrete composite beam-to-column joints with end-plate connections

Abstract

The application of stainless steel in construction has attracted steadily increasing interests over the past few decades. Compared with conventional carbon steel, stainless steel has a number of advantages including excellent durability and corrosion resistance, higher ductility, enhanced fire performance and reduced life cycle maintenance cost. However, the relatively high cost of production has long been restricting the broader application of stainless steel in structural engineering. This drawback could be partially overcome by stainless steel-concrete composite structures, which could provide a cost-efficient and sustainable solution for future steel and composite construction. In line with this background, this thesis focuses on the behaviour and design of bolted beam-to-column joints in stainless steel-concrete composite structures. A complete series of investigations are carried out from basic structural components, i.e. stainless steel bolts, to bare stainless steel end-plate connections (joints) and stainless steel-concrete composite joints. For stainless steel bolts, more than 300 bolt samples (complete bolts or machined coupons) are tested under tension, shear and combined action. The tested bolts include commonly used austenitic grades (A4-70 and A4-80) as well as high strength austenitic and duplex grades which are yet to be incorporated in existing design standards. The test data are subsequently used to appraise the applicability of the current design provisions which were initially developed for carbon steel bolts. Modified design formulae are thereafter proposed to predict the strength of stainless steel bolts. Following the investigation on stainless steel bolts, six full-scale tests are conducted for bare stainless steel joints with flush and extended end-plate connections. A particular focus is placed on the ultimate behaviour and rotation capacity of the joints. The materials of the fabricated sections (austenitic or lean duplex) and bolts (austenitic and duplex) are carefully selected to ensure a consistency of corrosion resistance within each of the joints. The experimental tests are supplemented by a comprehensive numerical parametric analysis incorporating an advanced fracture simulation technique. For stainless steel-concrete composite joints, three full-scale tests are conducted along with more than 100 numerical analyses performed based on finite element models. The main variable considered in the tests and analyses include the material of bolts and members (austenitic or lean duplex), the section of column (I-section or concrete-filled steel tubular section), the shear connector type (welded stud or bolted shear connector), and the reinforcement ratio of the slab. Based on the experimental and numerical data, a detailed assessment is carried out regarding the applicability of existing design methods (initially developed for carbon steel joints) to bare stainless steel and stainless steel-concrete composite joints. Simple modifications to the original method are proposed in order to make more reasonable predictions for stainless steel-concrete composite joints.