Experimental and analytical assessment of ductility in lightly reinforced concrete members

This is the post-print version of the final paper published in Engineering Structures. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.This paper is concerned with the ultimate behaviour of lightly reinforced concrete members under extreme loading conditions. Although the consideration given to the assessment of ductility is of general relevance to various applications, it is of particular importance to conditions resembling those occurring during severe building fires. The main purpose of the investigation is to examine the failure of idealised members representing isolated strips within composite floor slabs which become lightly reinforced in a simulated fire situation due to the early loss of the steel deck. An experimental study, focusing on the failure state associated with rupture of the reinforcement in idealised concrete members, is presented. The tests enable direct assessment of the influence of a number of important parameters such as the reinforcement type, properties and ratio on the ultimate response. The results of several tests also facilitate a detailed examination of the distribution of bond stresses along the length. After describing the experimental arrangements and discussing the main test results, the paper introduces a simplified analytical model that can be used to represent the member response up to failure. The model is validated and calibrated through comparisons against the test results as well as more detailed nonlinear finite element simulations. The results and observations from this investigation offer an insight into the key factors that govern the ultimate behaviour. More importantly, the analytical model permits the development of simple expressions which capture the influence of salient parameters such as bond characteristics and reinforcement properties, for predicting the ductility of this type of member. With due consideration of the findings from other complementary experimental and analytical studies on full slab elements under ambient and elevated temperatures, this work represents a proposed basis for developing quantified failure criteria.Engineering and Physical Sciences Research Council (EPSRC

Experimental Evaluation of the Mechanical Properties of Steel Reinforcement at Elevated Temperature

This paper describes an experimental investigation into the influence of elevated temperatures on the mechanical properties of steel reinforcement. The study includes tests carried out at ambient temperature as well as under steady-state and transient elevated temperature conditions. A complementary test series, in which the residual post-cooling properties of reinforcing bars were examined, is also described. The experimental study focussed on assessing the performance of reinforcement of 6 and 8 mm diameter, although 10 mm bars were also considered in some cases. The specimens included both plain and deformed bars. After providing an outline of the experimental set-up and loading procedures, a detailed account of the test results is presented and discussed. Apart from the evaluation of stress–strain response and degradation of stiffness and strength properties, particular emphasis is given to assessing the influence of temperature on enhancing the ductility of reinforcement. The findings of this study have direct implications on procedures used for predicting the ultimate behaviour of structural floor elements and assemblages during, and following, exposure to elevated temperatures

Bond behaviour of austenitic stainless steel reinforced concrete

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. 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. However, 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 bond behaviour of stainless steel reinforced concrete, to achieve more sustainable and reliable design methods for reinforced concrete structures. This paper investigates the bond behavior 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 very 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 rebar, so that more efficient designs can be achieved. Moreover, a summary of recommendations for the codes of practice is provided

Structural performance of stainless steel reinforced concrete members: A review

Degradation of reinforced concrete (RC) infrastructure because of corrosion of the steel reinforcement is a well-known and expensive global problem. The inspection, repair, maintenance and replacement costs are a huge drain on resources, while the consequent disruption damages productivity. Existing measures to improve the performance of failing RC structures are generally retrospective and do not aid the sustainability agenda, nor do they effectively reduce the maintenance requirements over the remaining design life of the structure. In light of this, the replacement of traditional, corrodible, carbon steel reinforcement with inherently corrosion-resistant stainless steel reinforcement in the design of concrete structures and infrastructure is a viable and attractive solution. There has been a rapid increase in interest in this topic in recent years from the engineering research community, mainly owing to the growing problem of aging and deteriorating infrastructure as well as the lack of available and appropriate performance data and design guidance for stainless steel reinforced concrete. This paper presents a state-of-the-art review of stainless steel reinforced concrete, both at a material and structural level and assembles and thoroughly reviews the known information as well as identifying the key gaps. The paper is aimed at both the research community, to drive future research agendas, as well as practicing engineers so they can employ sustainable and maintenance-free stainless steel reinforced concrete more readily and with confidence

Flexure Response of Stainless-Steel-Reinforced Concrete (SSRC) Beams Subjected to Fire

This paper examines the behavior of stainless-steel-reinforced concrete (SSRC) flexural members subjected to fire. Stainless steel (SS) reinforcement has gained popularity due to its corrosion resistance and long maintenance-free life. However, there is an insufficiency of performance data and design guidance in the present literature. This paper presents a numerical assessment of SSRC structural elements using a material model based on experimental tests. A finite element model was utilized to simulate and analyze the response of SSRC beams under fire. This study compared the behavior of SSRC beams with traditional carbon-steel-reinforced concrete (CSRC) beams, demonstrating that SSRC members have a higher load carrying capacity and can sustain fire exposure for longer durations. Additionally, SSRC beams exhibited higher deflections during fire exposure compared to CSRC beams

Ultimate behaviour and serviceability analysis of stainless steel reinforced concrete beams

Stainless steel reinforcement has become a very attractive option for reinforced concrete structures owing to its distinctive properties including outstanding corrosion resistance, excellent fire behaviour, long life cycle as well as low maintenance requirements. Additionally, stainless steel reinforcement offers exceptional ductility and strain hardening characteristics compared with other common materials, which are very desirable in design to avoid sudden collapse. However, most global design standards do not incorporate an appropriate design approach for reinforced concrete members with stainless steel. The substantial strain hardening characteristics of stainless steel are typically not represented in standardised material models and therefore this attractive characteristic is not exploited in design resulting in structural and economic inefficiencies. Hence, the aim of this paper is to propose and validate a new deformation-based design approach for stainless steel reinforced concrete beams based on the continuous strength method, with reference to the current design rules provided in Eurocode 2. This approach is shown to be an effective design tool that exploits the distinctive characteristics of stainless steel reinforcement in an efficient and reliable manner. It is shown to provide a more efficient design with less over-conservatism and greater accuracy, compared with other methods. A comprehensive parametric study is conducted using Abaqus software to study the influence that various geometric and material properties have on the capacity of the members. Moreover, the serviceability limit state is also explored through a detailed analysis of the deflection behaviour

Experimental investigation on the flexural behaviour of stainless steel reinforced concrete beams

The durability of reinforced concrete (RC) structures and infrastructure has been the subject of significant attention from the engineering research community in recent years, mainly owing to the deterioration of RC elements due to corrosion of the embedded steel reinforcement. In this context, stainless steel reinforcement can provide an efficient solution to enhance the expected lifetime of concrete structures, reducing the damage due to corrosion of the reinforcement and carbonation and deterioration of the concrete. However, current international design standards for reinforced concrete structures do not include appropriate guidance for stainless steel reinforced concrete (SSRC). In order to investigate the behaviour of stainless steel RC beams, a series of six beam tests was conducted and is discussed herein. The key performance measures for RC beams such as load-deflection response, cracking behaviour and deflections at service load are assessed. The validity and applicability of existing design rules, which were developed for carbon steel RC, are also examined for stainless steel reinforced concrete members. Other recently developed design procedures, based on the Continuous Strength Method and including an accurate material model for the stainless steel bars, are also examined

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

Yb-Fibre Laser Welding of 6 mm Duplex Stainless Steel 2205

Copyright © 2016 The Author(s). Duplex stainless steel (DSS) is one of the materials of choice for structural and nuclear applications, having high strength and good corrosion resistance when compared with other grades of stainless steel. The welding process used to join these materials is critical as transformation of the microstructure during welding directly affects the material properties. High power laser welding has recently seen an increase in research interest as it offers both speed and flexibility. This paper presents an investigation into the important parameters affecting laser welding of DSS grade 2205, with particular focus given to the critical issue of phase transformation during welding. Bead-on-plate melt-run trials without filler material were performed on 6mm thick plates using a 5 kW Yb-fibre laser. The laser beam was characterized and a Design of Experiment approach was used to quantify the impact of the process parameters. Optical metallographic methods were used to examine the resulting microstructures