Experimental Testing of Realistically Sized and Loaded FRP-Confined Prismatic Reinforced Concrete Columns

Abstract

An investigation into the achievable gain in axial strength capacity of FRP-confined prismatic reinforced concrete columns compared to unconfined columns when subject to axial and axial-flexural loading has been performed. An experimental test matrix of small-, medium-, and large-scale specimens addressed; size effect, load eccentricity and cross-sectional aspect ratio, allowing for detailed study of the cross-sectional behavioural mechanics and generation of an analytical model capturing the evolution of the cross-sectional behaviour.Experimental results demonstrated that an increase in axial capacity of 48% was achievable in axially loaded specimens, but was limited by cross-sectional geometry, and inevitable second order effects, that were more extensive with increasing load eccentricity. There was a corresponding reduction in confinement effectiveness, thus more FRP plies or straps are required when subject to large bending. Furthermore, with increasing load eccentricity, there is a beneficial increase in lateral deformation capacity. All specimens of rectangular cross-section benefit from FRP-confinement but this decreases with increasing aspect ratio. Lastly, experimental testing highlighted the importance of debonding, as the side length of the specimen between corners increases, small areas to the whole side of the specimen detached.Confinement of prismatic columns is achieved using the resistance generated in the FRP jacket as the concrete laterally expands, generating confining stresses at the convex corners under axial loading. Analysis of FRP strains at mid-height of the specimen show the formation of a cruciform shape originating at the corners, along the diagonals of the cross-section. As eccentric load is applied, the strains evolve into the higher compressive region, moving the effectively confined area over into this compressive region. Variation of the cross-sectional aspect ratio also dictates a change in effectively confined area, with higher strains generated next to the shorter side lengths. This complex behaviour necessitates research into large-scale specimens as the size effect does not encourage scaling of results from small-scale testing.

Date of Award	23 Nov 2016
Original language	English
Awarding Institution	University of Bath
Supervisor	Antony Darby (Supervisor) & Tim Ibell (Supervisor)