No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
Due to their various advantages including excellent corrosion resistance and high strength-to-weight ratios, fibre-reinforced polymer (FRP) composites have been widely used as bonded external reinforcement to enhance the performance of concrete, masonry, metallic and timber structures. In addition, FRP composites have attracted increasing attention for use in the construction of highperformance new structures. In particular, the combined use of FRP composites with one or more traditional materials to create hybrid structural systems is a promising direction for new structures in coastal/marine and other severe environments. This presentation will provide a summary of recent research advances in both areas at The Hong Kong Polytechnic University (PolyU). In the area of strengthening and retrofit of reinforced concrete (RC) structures with externally bonded FRP reinforcement, the following topics will first be covered: (1) suppression of debonding failures; (2) fire resistance and reliability-based design; (3) computational models for FRP-confined concrete and FRP-confined RC columns; (6) Seismic retrofit. Some fundamental issues in the strengthening of steel members with externally-bonded carbon FRP plates/sheets are then discussed. Finally, strengthening of RC beams with near-surface mounted carbon FRP (CFRP) strips, a more recent alternative technique to externally boned FRP reinforcement, is examined. In the area of new construction, this presentation will be focused on structural members based on concrete-filled FRP confining tubes manufactured using the filament winding process. These FRP tubes have fibres oriented close to the hoop direction, so their main functions are to confine the concrete, enhance the shear resonance, protect the column against corrosion, and serve as the stay-inplace formwork. Particular attention will be paid to hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) which consist of a layer of concrete sandwiched between an outer FRP tube and an inner steel tube. The presentation will conclude with an outline of some future opportunities and challenges in the structural use of FRP composites in construction. For example, the use of FRP reinforcement in new structures made of sea-sand seawater concrete should be an interesting area to explore.
Structural members with confined concrete are becoming increasingly popular in civil engineering applications because of their superior strength and ductility. In these structural members, the concrete is subjected to dilation-induced (passive) lateral compressive stresses from the confining device (e.g., a steel tube). Existing research has led to theoretical models that predict closely the stress–strain behavior of concrete under uniform confinement (e.g., concrete in circular steel tubes under concentric axial compression), but theoretical models with a similar capability have not been achieved for the more common situation of concrete under non-uniform confinement (e.g., concrete in rectangular steel tubes). This paper presents a three-dimensional (3D) plasticity constitutive model that is accurate in predicting the stress–strain behavior of concrete in various scenarios of confinement. In the proposed model, a well-established open strength surface with associated open yield surfaces is combined with a hardening/softening rule compatible with both plastic volumetric compaction and dilation. In addition, a novel potential surface with a triangle-like deviatoric trace is proposed and calibrated with available experimental data of non-uniformly confined concrete. The implementation of the constitutive model in finite element analysis with an enhanced stress-return algorithm suitable for the novel potential surface is explained. While the focus of the present work is on monotonic compression-dominated loading, the model can be combined with fracture and damage theories to depict the behavior of concrete under tension-dominated and cyclic loading conditions. The performance of the proposed model is evaluated by comparing its predictions with a wide range of experimental data covering uniform active, uniform passive, and non-uniform passive confinement conditions, which demonstrates the capability and high accuracy of the proposed model.
For the passage of utility ducts and/or pipes, openings often need to be created in the web of a reinforced concrete (RC) beam. Such a web opening can lead to a significant decrease in the ultimate load (i.e., strength) of the beam due to the reduced cross-sectional area and/or the severing of some of the existing steel reinforcement (particularly stirrups). In such cases, an externally-bonded fibre-reinforced polymer (FRP) strengthening system may be installed around the web opening to ensure the safety of the weakened beam. While existing experimental and numerical studies have provided useful information on the structural behaviour of RC beams with an FRP-strengthened web opening, this paper presents a theoretical study on the strength of such beams. First, a relatively simple, iterative numerical procedure (referred to as the iterative method) based on the static method of plastic limit analysis for predicting the plastic limit load (i.e., strength) of RC beams with an FRP-strengthened web opening is proposed, and then a closed-form, algebraic strength equation (referred to as the strength model) for such beams is established as a simplified approach of the iterative method. The accuracy of the proposed iterative method and strength model is verified with test results.
Extensive research has been conducted on fiber-reinforced polymer (FRP)-confined plain and RC columns, leading to a large number of stress–strain models. Most of these models have been developed for FRP-confined plain concrete and are thus applicable only to concrete in FRP-confined RC columns with a negligible amount of transverse steel reinforcement. The few models that have been developed for concrete under the combined confinement of FRP and transverse steel reinforcement are either inaccurate or too complex for direct use in design. This paper presents an accurate design-oriented stress–strain model for concrete under combined FRP-steel confinement in FRP-confined circular RC columns. The proposed model is formulated on the basis of extensive numerical results generated using an analysis-oriented stress–strain model recently proposed by the authors and properly captures the key characteristics of FRP-steel-confined concrete as revealed by existing test results. The model strikes a good balance between accuracy of prediction and simplicity of form and is shown to provide close predictions of test results and perform significantly better than existing stress–strain models of the same type.
Firstly, a plastic-damage constitutive model for concrete complying with the laws of thermodynamics is proposed based on continuum damage mechanics theory. The damage constitutive equations, damage evolution equations and plastic deformation of concrete are derived. Secondly, Fiber damage analysis model(FDAM) for RC beam-column member is established by analyzing section of fiber beam column element, which was developed with VUEL subroutine based on ABAQUS/Explicit platform, with the uniaxial damage constitutive relations of concrete proposed in present paper being used. The member damage index is defined, which can describe the nonlinear damage behavior of RC members under any loadings. Accuracy of the model is identified preliminarily by comparing with the analysis results of solid element. Finally, a numerical analysis model based on finite element program ABAQUS combined with the proposed damage model is built to analyze the seismic damage of a high-rise structure, and the structure analysis results are compared to the data from shaking table test.
One important application of fibre reinforced polymer (FRP) composites in the retrofit of reinforced concrete (RC) structures is to provide confinement to columns for enhanced strength and ductility. As a result, many theoretical and experimental studies have been carried out on the compressive behaviour of FRP-confined concrete. This paper provides a critical review of existing studies on this subject, with the emphasis being on the revelation of the fundamental behaviour of FRP-confined concrete and the modelling of this behaviour. Although the paper is explicitly limited to concrete confined with FRP jackets in which the fibres are oriented only or predominantly in the hoop direction, many of the observations made in this paper are also applicable or relevant to concrete confined with FRP jackets with a significant axial stiffness, as found in concrete-filled FRP tubes as new columns.
Structurally deficient civil engineering infrastructure: Concrete, metallic, masonry and timber structures Fibre-reinforced polymer composites used in rehabilitation Surface preparation of component materials Flexural strengthening of reinforced concrete beams with fibre-reinforced polymer composites Shear strengthening of reinforced concrete beams with fibre-reinforced polymer composites Strengthening of reinforced concrete columns with fibre-reinforced polymer composites Design guidelines for fibre-reinforced polymer strengthened reinforced concrete structures Strengthening of metallic structures with fibre-reinforced polymer composites Strengthening of masonry structures with fibre-reinforced polymer composites Flexural strengthening application of fibre-reinforced polymer plates Durability of externally bonded fibre-reinforced polymer composite systems Quality assurance/quality control, maintenance and repair Case studies.
In the FRP strengthening of steel structures, cohesion failure in the adhesive is the preferred mode of debonding failure at FRP-to-steel interfaces so that the design theory can be established based on the properties of the adhesive. In this paper, results from a systematic experimental study are presented to exam-ine the effects of steel surface treatment and adhesive properties on the adhesion strength between steel and adhesive. The test results show that adhesion failure can be avoided if the steel surface is grit-blasted prior to bonding and the treated surface can be characterised using three key surface parameters.
7th International Conference on FRP Composites in Civil Engineering, CICE 2014, Vancouver, 20-22 August 2014
No abstract is provided for this article.
Extensive research has been conducted on the replacement of steel rebars with fibre-reinforced polymer rebars to eliminate the steel corrosion problem in conventional steel bar–reinforced concrete structures. However, as the performance of fibre-reinforced polymer rebars is substantially inferior in compression (due to issues such as fibre micro-buckling) than in tension, their use in concrete columns is generally not recommended; this poses a significant challenge when a steel-free structure is needed. This article presents a novel steel-free hybrid rebar developed at The Hong Kong Polytechnic University that overcomes the above-mentioned problem. Such a hybrid rebar typically consists of a central fibre-reinforced polymer rebar, an external fibre-reinforced polymer confining tube and an annular layer of high-strength cementitious material such as ultrahigh-performance concrete. To demonstrate the performance of these hybrid rebars, results from a series of preliminary tests and associated modelling work are presented in the article. These results indicate that (1) the fibre-reinforced polymer rebar at the centre is well supported against bar buckling and fibre micro-buckling, (2) the compressive strength of the fibre-reinforced polymer material can be fully mobilized and (3) the stress–strain response of hybrid rebars can be designed to resemble an elastic–plastic response with some post-yielding hardening.
