Stress-strain models for FRP-confined thermally damaged concrete

Fiber-reinforced polymer (FRP) jackets have been increasingly used for the strengthening and confinement of concrete columns. Despite extensive research efforts yielding various concrete confinement models that can be broadly classified as design- and analysis-oriented, an accurate model is lacking for the design of FRP-strengthened thermally damaged concrete columns. This paper presents a comprehensive review of existing experimental studies on FRP-confined thermally damaged concrete columns and collects a large database of the corresponding test results. Then, a theoretical analysis is conducted to evaluate the accuracy and reliability of typical concrete confinement models (originally proposed for undamaged concrete) through extensive comparisons with the corresponding test data. The analytical findings have revealed that none of the existing models can accurately predict the compressive behavior of FRP-confined thermally damaged concrete. Two novel confinement models, design-oriented and analysis-oriented, are proposed for FRP-confined thermally damaged concrete. These novel models have appropriately considered the effects of high-temperature exposure on the confining pressure of FRP jackets and the lateral deformation characteristics of thermally damaged concrete. The proposed models are then validated by comparing the model predictions with the corresponding test results, indicating that these models can accurately predict the compressive stress-strain responses and dilation behavior of FRP-confined thermally damaged concrete.