Analysis and design of stainless steel reinforced concrete structural elements

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonStainless 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.Jerash Universit

Reinforced Concrete Design with Stainless Steel

In the design of reinforced concrete structures, the bond property is crucial. This is important for achieving the composite action between the two materials constituents, allowing loads to be efficiently transmitted. The higher strain hardening and ductility capacity of stainless steel over mild steel are one of its major benefits. International design codes, such as Eurocode 2, do not provide a separate design model for concrete structures with stainless reinforcing bars. The background paper to Eurocode 2 highlighted that there is no technical reason of why the Eurocode 2 design model cannot be used in conjunction with other types of reinforcement, provided allowance is made for their properties and behaviour. While this notion is valid when using a mild steel reinforcing bar, it produces erroneous results when a stainless reinforcing bar with a lap splice is used in a reinforced concrete section. Even though there has been a large number of studies on the behaviour of structure with stainless steel in recent years, most of it has been on plain stainless-steel members rather than reinforced concrete or stainless-steel reinforced concrete with lap splice. As a result, the purpose of this chapter is to evaluate and compare the behaviour of stainless and mild steel reinforced concrete with and without lap splices

Reinforced Concrete Design with Stainless Steel

In the design of reinforced concrete structures, the bond property is crucial. This is important for achieving the composite action between the two materials constituents, allowing loads to be efficiently transmitted. The higher strain hardening and ductility capacity of stainless steel over mild steel are one of its major benefits. International design codes, such as Eurocode 2, do not provide a separate design model for concrete structures with stainless reinforcing bars. The background paper to Eurocode 2 highlighted that there is no technical reason of why the Eurocode 2 design model cannot be used in conjunction with other types of reinforcement, provided allowance is made for their properties and behaviour. While this notion is valid when using a mild steel reinforcing bar, it produces erroneous results when a stainless reinforcing bar with a lap splice is used in a reinforced concrete section. Even though there has been a large number of studies on the behaviour of structure with stainless steel in recent years, most of it has been on plain stainless-steel members rather than reinforced concrete or stainless-steel reinforced concrete with lap splice. As a result, the purpose of this chapter is to evaluate and compare the behaviour of stainless and mild steel reinforced concrete with and without lap splices

Description of the constitutive behaviour of stainless steel reinforcement

This paper presents a comprehensive analysis of the constitutive relationship of stainless steel reinforcement and proposes new material models for both austenitic and duplex stainless steel bars. These are an advancement on existing models which have largely been developed for structural stainless steel plate, rather than for reinforcement bars. Current design guidance for material modelling of reinforcing bars does not include representative stress-strain relationships which capture the unique mechanical properties of stainless steel reinforcement. Codes include idealised elastic-plastic material models which are inappropriate and inefficient for the highly nonlinear and ductile material response of stainless steel. The present study aims to address this issue by first conducting a series of tensile tests to ascertain the stress-strain material responses and then employing this data to examine the validity of existing approaches and propose new material models where required. It is shown that new material models are required and those that are developed are able to accurately capture the stress-strain response of stainless steel reinforcement, and provide a better, more accurate, representation than existing methods

Durability Enhancement of Concrete with Recycled Concrete Aggregate: The Role of Nano-ZnO

The replacement of virgin aggregate with recycled concrete aggregate (RCA) in concrete mixtures offers an eco-strategy to mitigate the environmental limitations linked with traditional recycling techniques of RCA. However, the inferior properties of RCA, in contrast to virgin aggregate, present an obstacle to efficiently proceeding with this approach. Therefore, the aim of this study is to enhance the characteristics of concrete that contains RCA using nano-ZnO particles. Virgin aggregate was replaced with RCA in 30 wt.% and 50 wt.% ratios, followed by the addition of 0.5 wt.% nano-ZnO. The performance of concrete mixtures was evaluated in terms of their physical, mechanical, and durability properties. The addition of nano-ZnO particles to concrete with RCA resulted in refining its pore structure and reducing its water absorption, where the impermeability of concrete with 30 wt.% and 50 wt.% treated RCA decreased by 14.5% and 18%, respectively. Moreover, nano-ZnO treatment increased the compressive strength of mixtures with 30 wt.% and 50 wt.% RCA by 2.8% and 4%, respectively. All mixtures underwent a reduction in their 28-day compressive strength after exposure to a 5% sulphuric acid solution, where concrete with 30 wt.% and 50 wt.% RCA showed 20.2% and 22.8% strength loss, respectively. However, there was a 17.6% and 19.6% drop in the compressive strength of concrete with 30 wt.% and 50 wt.% RCA and treated with nano-ZnO

Prediction of the cross-sectional capacity of cold-formed CHS using numerical modelling and machine learning

The use of circular hollow sections (CHS) have seen a large increase in usage in recent years mainly because of the distinctive mechanical properties and unique aesthetic appearance. The focus of this paper is the behaviour of cold-rolled CHS beam-columns made from normal and high strength steel, aiming to propose a design formula for predicting the ultimate cross-sectional load carrying capacity, employing machine learning. A finite element model is developed and validated to conduct an extensive parametric study with a total of 3410 numerical models covering a wide range of the most influential parameters. The ANN model is then trained and validated using the data obtained from the developed numerical models as well as 13 test results compiled from various research available in the literature, and accordingly a new design formula is proposed. A comprehensive comparison with the design rules given in EC3 is presented to assess the performance of the ANN model. According to the results and analysis presented in this study, the proposed ANN-based design formula is shown to be an efficient and powerful design tool to predict the cross-sectional resistance of the CHS beam-columns with a high level of accuracy and the least computational costs

Correction to: Reinforced Concrete Design with Stainless Steel

In the design of reinforced concrete structures, the bond property is crucial. This is important for achieving the composite action between the two materials constituents, allowing loads to be efficiently transmitted. The higher strain hardening and ductility capacity of stainless steel over mild steel are one of its major benefits. International design codes, such as Eurocode 2, do not provide a separate design model for concrete structures with stainless reinforcing bars. The background paper to Eurocode 2 highlighted that there is no technical reason of why the Eurocode 2 design model cannot be used in conjunction with other types of reinforcement, provided allowance is made for their properties and behaviour. While this notion is valid when using a mild steel reinforcing bar, it produces erroneous results when a stainless reinforcing bar with a lap splice is used in a reinforced concrete section. Even though there has been a large number of studies on the behaviour of structure with stainless steel in recent years, most of it has been on plain stainless-steel members rather than reinforced concrete or stainless-steel reinforced concrete with lap splice. As a result, the purpose of this chapter is to evaluate and compare the behaviour of stainless and mild steel reinforced concrete with and without lap splices