Analysis and design of stainless steel reinforced concrete structural elements

Abstract

Stainless steel reinforced concrete has seen a large increase in usage in recent years, in response to the ever-increasing demands for structures and infrastructure to be more durable, efficient and sustainable. Stainless steel has excellent corrosion resistance, as well as many other distinctive properties such as excellent strength and ductility, ready availability and a long, low-maintenance, life cycle. On the other hand, one of the fundamental challenges that dramatically limits the lifetime and reliability of traditional carbon steel reinforced concrete is corrosion of the reinforcement, especially in harsh environments such as coastal, marine or industrial settings. With the increased focus on environmentally conscious and reliable design, stainless steel reinforcement represents an ideal solution for the corrosion and deterioration problems faced by reinforced concrete structures, as well as the associated maintenance issues. However, it is also has a higher initial cost, and therefore needs to be used carefully and efficiently. The existing material models provided for the structural analysis of reinforced concrete members in current design standards, such as Eurocode 2, are not appropriate for stainless steel reinforced concrete and lead to inaccurate predictions of the section capacity. Generally, there is a lack of data in the public domain regarding the behaviour of concrete beams reinforced with stainless steel, mainly owing to this being a relatively new and novel topic. This is especially true for the important issue of bond strength and the relationship that exists between the reinforcement and the surrounding concrete. Currently, existing design standards advise using the same design rules for stainless steel reinforced concrete as traditional carbon steel reinforced concrete, owing to a lack of alternative information, although this is not based on test or performance data. As such, there is a real need to develop a full and fundamental understanding of the behaviour of stainless steel reinforced concrete, to achieve more sustainable and reliable design methods for reinforced concrete structures. In this context, this thesis provides a detailed background of the existing information on stainless steel reinforced concrete, as well a discussion on the potential advantages and challenges. Then, attention is given to analysing the behaviour of stainless steel reinforced concrete beams by developing the Continuous Strength Method to predict the bending moment capacity. A finite element model has been developed in order to further assess the performance, and this is also used to conduct a parametric study of the most influential properties. It is concluded that the proposed analytical models provide a reliable solution for predicting the capacity of concrete beams reinforced with stainless steel. In addition, this thesis investigates the bond behaviour of stainless steel reinforced concrete and compares the performance to traditional carbon steel reinforced concrete, through experimental testing and analysis. It also compares the results to existing design rules in terms of bond strength, anchorage length and lap length. It is shown that stainless steel rebar generally develops lower bond strength with the surrounding concrete compared with equivalent carbon steel reinforcement. Moreover, it is shown that existing design codes are extremely conservative and generally underestimate the actual bond strength by a significant margin. Therefore, following detailed analysis, it is concluded that current design rules can be safely applied for stainless steel rebar, although more accurate and efficient methods can be achieved. Hence, new design parameters are proposed reflecting the bond behaviour of stainless steel rebars, so that more efficient designs can be achieved.