Reliability Analysis of RC Columns and Frame with FRP Strengthening Subjected to Explosive Loads

Some structures, both military and civilian, might experience explosive loads during their service life. Owing to high uncertainties in blast load predictions and structural parameters, accurate assessment of the performances of structures under explosion loads is a challenging task. For example, a number of experimental studies using fiber-reinforced plastic (FRP) strengthening of RC structures have been reported in the literature. Most of these studies demonstrate that FRP strengthening is effective in increasing the blast load-carrying capacities of RC structures. However, significant variations in the effectiveness of FRP strengthening have also been observed owing to the large uncertainties in blast loading, RC and FRP material properties, and workmanship in preparing the test specimens and conducting experimental tests. Very few studies that take into consideration these uncertainties in analyzing the effectiveness of FRP strengthening of RC structures on blast loading resistance can be found in the literature. This study performs a reliability analysis to assess the performance of RC columns with or without FRP strengthening in resisting blast loads. Statistical variations of blast loading predictions derived in a previous study are adopted in this study. To define structural performance, pressure-impulse (P-I) curves with a damage criterion on the basis of axial load-carrying capacity that were developed in previous studies for RC columns without strengthening or with FRP strip, FRP wrap, or both FRP strip and wrap strengthening are used. Considering the uncertainties in blast loading predictions and RC column and FRP material properties and dimensions, limit-state functions corresponding to different damage levels of RC columns with or without FRP strengthening are formulated. The statistical variations of blast loading, RC column dimension, longitudinal and transverse reinforcement ratio, and concrete, steel, and FRP material strength and FRP thickness are considered. The failure probabilities of RC columns corresponding to different damage levels with or without FRP strengthening are calculated. The effectiveness of FRP strengthening on the RC column's blast loading resistance capacities is discussed. The importance of considering the random fluctuations on blast loading and RC column parameters in assessing the blast loading effect on RC columns is demonstrated. A structural system reliability analysis is also carried out to examine the probability of structural collapse as a result of blast loading applied to the front of an example two-span multistory RC frame. The results obtained in this study demonstrate the effectiveness of FRP strengthening on structure protection and can also be used to assess RC structure performance under blast loadings.