Cyclic axial behavior of concrete columns confined with FRP sheets or with a combination FRP sheets and anchors -

Abstract

Confining concrete columns with external fiber reinforced polymer (FRP) jackets is a well-known technique widely used in strengthening and repairing existing columns. This method relies on the fact that concrete is a pressure-sensitive material that has its axial load capacity and axial failure ductility improved when provided with a confining pressure. In the last two decades, many experimental and analytical studies have been carried out to evaluate the efficiency of FRP in enhancing columns strength and ductility. Most of these studies have concentrated on FRP-confined concrete specimens subjected to monotonic loading. Also, many analytical and design-oriented models have been proposed to describe the axial stress-strain behavior of FRP-confined concrete. However, most of the available models considered the case where the confinement level provided by the FRP leads to improvement of the concrete’s ultimate strength resulting in post peak ascending behavior, very few predicted a post peak descending behavior and none of them predicted the cyclic stress-strain response for FRP confined rectangular column sections. Accordingly, guided by the test results of an experimental program performed at AUB and other test data reported in the technical literature, an axial stress-strain material model of FRP-confined concrete under cyclic loading is developed and validated, which constitutes the first part of this investigation. The model covers all important parameters in a unified manner, and predicts both ascending and descending post peak responses. Despite the high efficiency of external jacketing in enhancing the strength and ductility of columns of circular cross-sections, its efficiency gets reduced when used to confine specimens of non-circular cross-sections. This is attributed to the fact that an externally-wrapped circular cross-section is fully and uniformly confined, however only part of an externally-wrapped rectangular cross-section is effectively confined. For FRP confined concrete columns