Modelling of SFRC using inverse finite element analysis

A method of inverse finite element analysis is used to determine the constitutive relationship of SFRC in tension, using primary experimental data. Based on beam bending test results and results from pull-out tests, an attempt is made to explain the physical processes taking place during the cracking stage. Basic models predicting the behaviour of SFRC in tension are proposed. © RILEM 2006

Reuse of tyre steel fibres as concrete reinforcement

To attain economically viable and environmentally friendly tyre recycling, it is necessary to develop new applications and products, which will use tyre by-products (especially the steel cord) as raw materials. The authors demonstrate that the steel fibres recovered from used tyres can be used to reinforce concrete elements. This application has a great potential, as it is estimated that more than 500000 t of high-quality steel fibres could be recovered annually from used tyres in the EU alone. This paper presents the work carried out as part of various ongoing projects on the use of steel fibres in concrete construction. The first part of the paper deals with waste management issues, the methods used to recover steel fibres from tyres, and existing applications of used tyres. The second part presents the mechanical behaviour of concrete elements reinforced with these steel fibres and discusses the relevant design and economic issues. It is concluded that the use of these steel fibres in concrete construction will benefit not only the construction industry, but also the producers and recyclers of used tyres

Behaviour of concrete columns with drilled holes

Holes drilled out to install additional services or equipment, such as for ducts through columns, beams or walls, can lead to loss of strength and possible structural failure. Until now little work has been done on holes in columns and, hence, the present study aims to examine the amount of strength lost owing to the presence of holes in columns. The reported experimental work deals with different parameters such as the number and dimensions of the holes and their relative position. It is shown that, for large diameter holes, a section capacity loss of up to 50% is possible. © 2006 Thomas Telford Ltd

Design issues for concrete reinforced with steel fibers, including fibers recovered from used tires

The writers are investigating the use of steel fibers, recovered from used tires (RSF), as concrete reinforcement, aiming at the development of design recommendations. This paper presents part of this research and examines initially an existing design guideline, developed by RILEM for steel fiber-reinforced concrete (SFRC), in order to assess the suitability of the guideline for the flexural design of concrete reinforced with RSF (RSFRC). This examination indicates that, although the RILEM guideline is in general suitable for the flexural design of RSFRC, there are some fundamental issues related to the evaluation of the tensile stress-strain behavior of SFRC that affect the accuracy of the guideline. Thus, based on this conclusion, a new approach is outlined for the evaluation of the tensile stress - strain behavior of SFRC and models are derived for different types of RSF and industrially produced fibers. These models are applied to the flexural design of concrete reinforced with RSF (RSFRC) and results are compared with those obtained by using the RILEM tensile stress-strain models. It is concluded that the model proposed in this study is more conservative and accurate than the RILEM models. Recommendations are also made on values of tensile strain to be used as the ultimate limit state, when predicting the resistance capacity of SFRC and RSFRC. © 2006 ASCE

Failure-mode-hierarchy-based design for reinforced concrete structures

Innovations in concrete construction can be held back by the inability of codes of practice to accommodate new materials. The current design and safety philosophy (DSP) of reinforced concrete relies heavily on the properties of steel reinforcement. The need to embrace new materials, such as fibre-reinforced polymer (FRP) reinforcement, led to an in-depth examination of the DSP of European concrete codes of practice and resulted in a new philosophy, presented in this paper. The basis of the new philosophy remains the limit-state design and achievement of target notional structural reliability levels, but aims at the attainment of a desired failure mode hierarchy. The implementation of the philosophy, through a proposed framework, utilises the concept of average measure of closeness for the determination of appropriate material partial safety factors. An example of the application of the proposed framework is presented for FRP reinforcement. © 2005 Thomas Telford and fib

Design philosophy issues of fiber reinforced polymer reinforced concrete structures

The conventional design philosophy for reinforced concrete (RC) relies heavily on the ductile properties of steel. These ductile properties are used as a "fuse" and conceal the large uncertainty in the determination of modes of failure caused directly by concrete. Current design guidelines for fiber reinforced polymer (FRP) RC structures have inappropriately adopted the same design philosophy used for steel RC, leading either to the adoption of conservative safety factors or reduced structural reliability. A reliability-based analysis of FRP RC beams shows that the current, very conservative partial safety factors for FRP reinforcement on their own do not influence the structural safety of overreinforced concrete elements. Proposals are made for the modification of the material partial safety factors to achieve target safety levels

Structural safety uncertainties in codes of practice for reinforced concrete

The limit-state design approach, currently used in codified design of concrete structures reinforced with steel reinforcement, is based on semi-probabilistic procedures. Although modern concrete codes of practice are more sophisticated than older codes based on the permissible stress approach, they still have fundamental uncertainties with regards to structural safety. The work reported in this paper investigates these uncertainties for the BS 8110 and Eurocode-2 codes of practice by performing a structural reliability assessment using the Monte-Carlo Simulation method in conjunction with the Latin Hypercube and Conditional Expectation variance reduction techniques. The assessment considers both the flexural and shear failure modes. In the case of BS 8110, it is shown that it may be more appropriate to increase the characteristic value of the tensile strength of steel reinforcement rather than to use the reduced partial safety factor of 1.05. © Kyriacos Neocleous, Kyprous Pilakoutas, Peter Waldron

Thin FRP/GFRC structural elements

This paper presents background work leading to the development of thin structural elements made of GFRC (Glass Fibre Reinforced Concrete) reinforced with FRP (Fiber Reinforced Polymer) bars. Such thin structural elements are suitable for a variety of applications such as cladding, security screens, etc, but this paper focuses on their use as permanent formwork. The first part of the paper deals with optimising a uniform thickness GFRC section to achieve maximum flexural capacity at minimum weight. The second part deals with the interaction between FRP and GFRC, in particular with the issues of bond. The third part presents the performance of a 3 m span thin GFRC permanent formwork panel system reinforced with FRP. Both experimental and analytical studies are presented and it is concluded that FRP/GFRC thin structural elements can be designed using conventional techniques requiring only the use of appropriate material characteristics

FE modelling of bond interaction of FRP bars to concrete

In this paper a computational modelling approach is used to investigate the bond behaviour of fibre-reinforced plastic (FRP) bars in concrete. Two finite element packages (ANSYS and ABAQUS) are used to model the bond interaction of FRP reinforcing bars in cubes and beams. The main purpose of this work is to develop additional understanding of how FRP bars ‘cooperate’ with concrete to sustain the pullout load. Two modelling approaches are presented. In the first approach, a spring describing the behaviour of short embedment lengths in pullout tests was used for predicting the behaviour of longer embedment lengths. In the second approach, spring characteristics obtained from an experimentally determined bond stress against anchorage length envelope are used in FE modelling of beams. Both approaches showed good agreement between analytical and experimental results. However, further development on the analytical modelling of the bond interaction is required, in order to consider the effect of all parameters that influence bond

Assessment of Post-Restrained Shrinkage Mechanical Properties of Concrete

Restrained shrinkage induced cracks can cause issues with serviceability, structural integrity and durability in concrete, but are difficult to predict. This paper proposes a simple, and economical test rig for restrained shrinkage and associated procedures to assess the post-shrinkage mechanical properties (compressive and flexural strength) of concrete. The results show that the restraining factor of the proposed rig is dependent on the time and the stiffness of the concrete. Results of residual mechanical properties show that restrained shrinkage induced cracks can affect the mechanical behaviour (flexural and compressive strength and stiffness) of concrete by up to 21%