آنالیز تیرهای کامپوزیت فولاد-بتن ضد زنگ Analysis of stainless steel-concrete composite beams

1. Introduction This paper is concerned with the behaviour of composite beams made from stainless steel. Steel-concrete composite members are widely used in the design and construction of modern structures such as bridges and high rise buildings. Depending on the degree of composite action, a significant increase in strength and stiffness performance is gained compared to a bare steel or concrete section. This results in savings not only in construction depth but also in terms of material consumption, which means also lower environmental impact and reduced energy consumption [1]. Composite beams which are subjected to positive bending (i.e. sagging) offer a particularly efficient use of the constituent materials. In this case, the steel section is subjected to tensile stresses whilst the concrete slab acts primarily in compression, thus utilising the favourable characteristics of each material. It is generally desirable for plastic design that composite beams have a ductile cross-section, in which strain hardening develops in the lower flange before the collapse moment is reached [2]. However, for calculating the load-bearing capacity of composite beams, design codes such as Eurocode 4 [3] generally neglect strain hardening effects and employ a rigid-plastic analysis of the cross-section, thus providing conservative predictions of the capacity in many cases, particularly when ductile materials such as stainless steel are employed. Stainless steel has been employed in construction since the 1920s, when the main usage was in building facades. Nowadays, stainless steel has become popular in a wide range of construction and load-bearing applications due to its excellent mechanical properties such as higher strength and ductility, better retention of strength and stiffness at high temperature [4] and excellent corrosion resistance properties, compared with carbon steel. Stainless steel does not require coatings to be applied, thus leading to life-cycle cost savings relative to carbon steel especially for offshore steel structures [5], as well as reducing maintenance and rehabilitation costs. In recent years, stainless steel has been the subject of intensive research in order to provide useful, efficient and reliable design guidance for engineers. The vast majority of research into stainless steel has been focussed on bare steel elements. Researchers have investigated the flexural behaviour of stainless steel columns subjected to compressive loading or combined compression and bending moment (e.g. [6–9]) and beams (e.g. [10–13]) as well as beams and columns under fire conditions (e.g. [14]). The use of stainless steel in composite structures has hitherto received little attention from the engineering community and research studies have generally been limited to investigating the behaviour of concrete-filled stainless steel columns under different loading conditions using experimental and numerical analysis. Lam et al. [15] conducted experiments on the behaviour of axially loaded concrete-filled stainless steel elliptical sections made from normal and high strength concrete. Uy et al. [16] carried out experiments on concrete-filled stainless steel circular, square and rectangular sections of short and slender columns subjected to combined axial compression and bending moment. The behaviour of concrete-filled stainless steel circular and square tubular sections subjected to axial compression under fire conditions has also been studied through a series of experiments [17]. Moreover, nonlinear finite-element analysis was used to investigate the performance of concrete-filled stainless steel tubular columns of square, L-, T-, and + shape sections under axial compression or combined compression and bending moment [18, 19]. To date, there has been no research available in the public domain on traditional composite beams (i.e. a bare steel section connected to a concrete slab through shear connectors) using stainless steel. The following section describes the context in which these members are highly relevant in the current era.