Hysteretic Uncertainty and Anomaly Quantification of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer and Ultra-High-Performance Concrete in Thermocyclic Distress

Seismic strengthening with carbon fiber reinforced polymer (CFRP) sheets is a proven technique for improving the capacity and ductility of concrete members and has been used worldwide. In this study, the effects of multi-hazard loading on the behavior of reinforced concrete beams strengthened with CFRP and ultra-high-performance concrete (UHPC) jackets are investigated. This work is an unprecedented initiative in the rehabilitation sector. Based on a previously conducted experimental study, where load reversals are performed at elevated temperatures varying from 25 to 175 ℃, analytical responses are investigated focusing on the performance degradation, uncertainty quantification, hysteresis, and pinching mechanisms of the retrofitted beams. The uncertainty index, which measures the extent of the anomaly caused by the multi-hazard loading, clarified that the pinching of hysteresis loops during loading processes is the predominant factor causing a loss of energy dissipation capacity in the thermocyclic distress. The development of uncertainty correlated with the degree of drift ratios, demonstrated by the increased uncertainty index of 0.37 at 175 ℃, and the beam pinching is controlled by the retrofit schemes. The adjusted stiffness of the loops represents the accumulated damage and deformation resistance; meanwhile, the evolution of irreversible pinching alters hysteretic configurations in the subsequent unloading phases. The Eigen hysteretic properties of the beams are extracted to understand the contribution of individual modes to the progression of uncertainties. The first mode dominates the fourth mode by a factor of up to 127.9. Design recommendations are suggested to estimate thermocyclic damage in the strengthened beams with performance degradation factors ranging from 1.00 to 0.45, contingent upon temperature.