FRP-confined capsule-shaped columns under axial and lateral loading

Abstract

The application of externally bonded fiber reinforced polymer (FRP) composites has achieved enormous popularity in recent times for the strengthening and repairing of old concrete bridges and buildings. Specifically, concrete columns and bridge piers in existing structures, which generally have inadequate transverse reinforcement as per old design codes, are vulnerable to seismic attacks and thus they need to be strengthened to enhance their strength and ductility. The externally bonded transverse FRP systems provide additional confinement which lead to an increase in the compressive strength, shear capacity and ductility of the confined columns and piers. Previous studies on FRP-confined columns indicated that the confinement effect is most significant in circular column sections and, to some extent, in square sections rather than in rectangular sections with large aspect ratios. But, in reality, many building columns and bridge piers are rectangular in shape with an aspect ratio of more than 1.5, and as large as 7, which may well be termed ?wall-like? columns. To enhance the confinement effect from FRP systems, reprofiling of rectangular columns is proposed herein by adding two circular concrete segments at the shorter sides and thus forming a capsule-shaped section before applying the transverse FRP reinforcement. The current thesis presents the details and results of a study on the FRP-confined capsule-shaped columns subjected to axial and lateral loads. The main parameters of the study were the effect of section geometry and the number of ply of transverse FRP sheets. The axial load tests showed significant enhancement in axial load capacities of capsule-shaped columns. The proposed confinement models are valid for circular, square, rectangular and capsule-shaped sections and they showed reasonable accuracy to predict the axial load capacity of tested columns. The pushover load tests on FRP-confined rectangular and capsule-shaped columns showed the effectiveness of transversely bonded FRP systems to prevent the shear failure and to enhance ductility significantly. The predicted load-displacement profiles matched very well with the experimental observations. The stiffness and strength degradations in cyclic load test of FRP-confined column were also prevented by the externally bonded FRP reinforcement. A finite element model of FRP-confined capsule-shaped columns was developed and calibrated using the cyclic response obtained from the test and hysteresis parameters were determined. Two case studies consisting of FE analysis of a building frame and a bridge pier were illustrated. In both studies, FRP confinement prevented the shear failure and enhanced the drift ratio of the structure. The seismic adequacy of FRP-confined pier was checked against the seismic demand for Northridge earthquake.