Effects of Variation of Axial Load and Bi-Directional Loading on the FRP Retrofit of Existing B-C Joints

Abstract eng:
Most of the experimental studies on the seismic assessment and retrofit of existing, poorly detailed, beam-column joints have typically concentrated on the 2-dimensional (2D) response, based on uni-directional cyclic loading testing protocol under constant axial load. However, in order to obtain a more realistic understanding of the behavior of deficient exterior beam-column joints prior and after retrofit intervention, consideration of the 3-dimensional (3D) response under a) bi-directional and b) varying axial loads are necessary. In this contribution, these two effects on the assessment and retrofit of exterior beam-column joints using GFRP composite materials are discussed. A series of 2/3 scale, 2D and 3D exterior (corner) beam-column joint subassemblies representative of pre-1970s construction practice were tested quasi-statically. Performance-based retrofit approach has been adopted in order to achieve the desired ductile failure mode by modifying the hierarchy of strength within the beam-column joint system. A critical comparison of the existing and retrofitted joints with regard to the observed damage and the global hysteresis behavior are shown, emphasizing the effects of axial load variation and bi-directional loading. The experimental results provided satisfactory confirmations of the efficiency of the proposed retrofit solution, aimed at protecting the panel zone region, while activating a flexural behavior in the beam in order to achieve a more desired weak beam-strong column global inelastic mechanism.

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