Thermomechanical-Coupled Distress for Reinforced Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer

This paper presents detrimental synergies resulting from mechanical distress coupled with elevated temperatures on the behavior of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. Thermal loadings ranging from 20 to 170 degrees C (68 to 338 degrees F) are associated with various mechanical loading configurations for 18 beams-monotonic, incremental cyclic, and anomalous cyclic. Of interest are the flexural responses, failure modes, and energy development of the strengthened beams subjected to the coupled loadings. The capacity of the beams decreases with an increase in temperature, whereas their individual performance is controlled by the mechanical loading schemes. A threshold temperature is noticed, which classifies the response domains of the cyclically loaded beams. The implications of the monotonic and cyclic loadings become similar above the threshold temperature due to the deteriorated CFRP-concrete interface. The failure modes of the beams are dominated by the thermal loading, rather than the mechanical loadings. Regarding the energy development of the test beams, the influence of the incremental cyclic loading is pronounced relative to its anomalous counterpart. The degree of energy dissipation tends to stabilize as long as the anomalous excitation does not exceed the magnitude of the sinusoidal cyclic loading. To characterize the performance of the strengthened beams under the thermomechanical-coupled loadings, an analytical approach is proposed.