Behaviour of Concrete Columns With Gfrp Circular and Rectilinear Confining Reinforcement

Abstract eng:
Glass Fibre-Reinforced Polymer (GFRP) bars are becoming a feasible alternative to steel bars to produce corrosion-free reinforced concrete structures. In an effort to assess the effectiveness of GFRP spirals and rectilinear ties as internal reinforcement in columns, an extensive research program is underway at the University of Toronto. In the experimental part of the program, fifteen 356 mm diameter full-scale circular columns and sixteen 305 mm x 305 mm cross-section square columns were constructed and tested under constant axial loading and cyclic lateral displacement excursions simulating earthquake load. The test parameters included column shape, types of longitudinal reinforcement (steel and GFRP bars), lateral reinforcement ratio, spacing and configuration of lateral reinforcement, and level of axial load. This paper compares the experimental results from a select group of the circular and the square concrete columns in which steel longitudinal reinforcement was used along with GFRP lateral reinforcement. Results are presented in the form of moment vs. curvature response and shear vs. lateral deflection behaviour. A number of ductility parameters related to curvature, displacement, energy dissipation and drift capacity were used to compare the seismic performance of the circular and square specimens. The drift capacity of the columns at failure was in the range of 2.5% to 3.1% for the columns presented here which satisfy the limitations of North American building codes with circular columns performing better than square columns. Strength degradation before the final collapse at large displacement was minimal for both square and circular columns primarily due to the continuing confinement provided by GFRP lateral reinforcement to the concrete core. Based on the data from the tests, it can be concluded that internal GFRP lateral reinforcement in many cases can provide better confinement and better performance of columns than provided by steel.

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