International Concrete Abstracts Portal

In order to investigate the seismic behavior of existing reinforced concrete (R/C) rectangular columns which are strengthened by circular steel jackets, a total of twenty column specimens with and without strengthening were designed, constructed, and were tested under three different constant axial-stresses of 5.6, 13.2 and 19.4 MPa, and alternately repeated lateral forces. Test results of retrofitted columns with circular steel jackets are compared with those obtained from the column specimens with and without rectangular steel- and CF sheet-jackets, and circular CF sheet jackets. One of the main conclusions is that the ultimate flexural strengths and deformation capacity of the R/C rectangular columns which are confined laterally by the circular steel- and CF sheet-jacketing are quite effective, especially in case of the columns under high axial-compression.

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.