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Modeling of FRP-jacketed RC columns subject to combined axial and lateral loads


To successfully use the fiber-reinforced-polymer (FRP) overlay technique for the seismic retrofit and the blast- hardening of RC columns, the mechanical behavior of the FRP-confined concrete needs to be understood and its response needs to be accurately predicted. Although a number of studies have been conducted to-date, it is still not clear how the main parameters affect the axial stress- strain response of a FRP-confined concrete cylinder. In particular, while it is understood that FRP jackets inhibit dilatancy, current models do not capture the physics that leads to ascending or strain-softening responses vs. the level of lateral confinement. In this dissertation, a dilatancy-based analytical model for FRP- jacketed circular concrete cylinders in axial compression was developed. The proposed theory is applicable to both the heavily confined case with ascending axial loaded vs. axial strain response, and the lightly confined specimen with strain-softening behavior. As an extension of the circular model, a new model for rectangular FRP-confined sections was then developed. In addition to jacket membrane strain, the jacket flexural strains caused by the cross-sectional shape were taken into account, and the rupture strain of the FRP jacket in the corner zone was predicted. The present model was validated via a large set of existing test results, and excellent agreement with experimental data was observed. As the application of the proposed concrete model, a load-displacement model and an associated computational algorithm were developed and validated for the response and failure conditions of RC columns subject to combined axial and seismic-type (lateral) loads. On the other hand, excluding the strain rate effects on material parameters from modeling, an analytical procedure was also developed to predict the resistance function of FRP-jacketed RC columns subject to combined axial and uniform lateral (simulated blast) loads. The model was validated via the results of the UCSD quasi-static tests on "blast columns", and satisfactory correlation with the experimental load-displacement curves were observed. The present models and the analytical procedures proposed in this dissertation can serve as design/analysis tools for the FRP overlay technique as applied to the seismic retrofit as well as the blast- hardening of RC columns

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