International Concrete Abstracts Portal

Over the past decade, fibre-reinforced polymer (FRP) composites have found wide applications in civil engineering, particularly in the retrofit of structures. One important application of FRP composites in the retrofit of reinforced concrete (RC) structures is to provide confinement to columns for enhanced strength and ductility. As a result, a large number of studies have been carried out on the compressive behaviour of FRP-confined concrete. This paper provides a state-of-the-art 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. Both monotonic loading and cyclic loading are covered, although only a limited amount of work is available on the latter. The paper is explicitly limited to concrete confined with FRP jackets, in which the fibres are oriented only or predominantly in the hoop direction, but many of the observations made in this paper are also relevant to concrete confined with FRP jackets with a significant axial stiffness, as found in concrete-filled FRP tubes as new columns.

This paper describes a series of tests on concrete cylinders confined by carbon fiber jackets. The primary variables in the investigation were the thickness of the jackets (and therefore the lateral confinement stress), the size of the cylinders, the loading speed, and the loading type (monotonic vs. cyclic), and the jacket type (individual layers or continuous wrap). Of these parameters, the lateral confining stress was found to have the greatest influence, but the coefficient for the concrete used was found to be slightly lower than the 4.1 that is implicit in ACI318-02. The cylinder size, the loading speed and the cyclic loading regimes were found to have essentially no influence on stress and strain at failure. The continuously wound jackets were found to initiate failure by delamination, rather than fracture of the fiber, and to lower the stress and strain at failure.

The use of high-strength concrete (HSC) tied columns is becoming increasingly popular in engineering practice. Researchers are working to obtain the proper post-peak behavior of tied columns with concrete strength greater than 60 MPa. Many empirical confinement models have been reported in the literature for the prediction of stress-strain behavior under concentric loading. However, nothing significant has been said about the numerical modeling of the problems wherein the nonlinear response of HSC tied columns may be reasonably predicted. In the present study, the nonlinear behavior of concrete material has been idealized by William-Warnke five-parameter model, which, to date, is the most widely accepted and sophisticated criterion. Within the framework of rate independent associative elasto- plasticity, a full backward Euler integration algorithm for stress updating has been implemented in the present work. A fixed crack smeared approach based upon fracture energy concept and non- local material softening law has been employed for the tensile modeling of concrete material. The computational model also involves the provision for cover spalling. A couple of examples have also been presented for validation of the numerical methodology proposed in this work.

It has been widely known that concrete filled steel tubular (CFT) columns have much higher strength and deformation capacities than common reinforced concrete (RC) columns because of beneficent interactive confinement effect between the filled concrete and the steel tube. The confinement effect by steel tube furthermore contributes to improving ductility of high-strength concrete, and enables application of the CFT columns in high-rise buildings located on seismic regions. This paper describes the axial and the flexural behaviors of CFT columns with circular and square sections based on many experimental researches conducted in Japan. The emphasis of this paper will be placed on the stress-strain curve models for concrete in CFT columns, which play the fundamental role in assessing both of the axial and the flexural behaviors of the CFT columns.

In order to evaluate the load carrying capacity and ductility of hinging zone ofthe concrete filled steel tubular (CFT) columns, tests are carried out on 12 circular speci-mens and 18 square specimens subjected to uniform bending under a constant axial load.The experimental parameters are: 1) depth to thickness ratio (D/t ratio) and width to thick-ness ratio (B/t ratio) of steel tube; 2) axial load ratio; 3) material strength; 4) deformationhistory and 5) annealing. One of the features of the test is the wide range of D/t and B/tratio. The range of D/t ratio of the circular CFT columns are 40.5-160 and the range of B/t ratio of the square CFT columns are 32.8-98.0, respectively. The experimental load-de-formation relations are compared with those of the elasto-plastic analysis based on theproposed stress-strain relationships established for the filled concrete and for the steel tube.The analytical results show good agreement with the test results for all specimens. Thisimplies that the proposed stress-strain relationships for CFT columns are useful to predictthe characteristics of the filled concrete and the steel tube.