Engineering structures are subjected to different loads during their lifetime, which may cause damage or secondary loading effects. Among loading effects on structures, explosion and earthquake may also cause fire. A damaged structure can experience a different response under fire loading in comparison to the intact structure. In addition to strength loss, damaged reinforced concrete (RC) frames may be exposed to cracking and spalling of concrete cover at various damage levels. These phenomena affect heat transfer in the structural section. In this study, Markov probability chain analysis is used to determine the probability of the occurrence of first failure in a 7-story RC frame damaged at different levels is evaluated under fire loading. The time of the first failure in structural elements is also calculated and presented for each damage level. The results show that increased damage levels in RC frame results in a greater probability of failure and reduced time of failure under fire loading scenario. The failure probability was found as zero at damage indices of 0, 0.1 and 0.2, with non-zero probabilities for greater damage indices. The framework developed in this paper outlines the performance assessment procedure for a damaged structure that is later exposed to fire loading. Manuscript profile

Since the analysis of underground structures in seismic conditions was more based on non-linear terrestrial environment and linear structure, regarding nonlinear behavior of soil and tunnel against earthquake was of paramount significance in order to achieve real responses in practice. The use of polypropylene fibers in concrete materials can help improve the performance of concrete members. In this regard, after verifying the behavioral model of fiber-reinforced concrete seen in the structure of the tunnel and using an article by Conforti et al., the nonlinear seismic analysis of the ground and the structure of the water transmission tunnel of Amirkabir Dam to Tehran refinery no. 6 was performed by a time-history method and through ABAQUS software and concrete damage plasticity model for concrete lining and mohr-coloumb model for host soil of tunnel. Simulations were performed for the fibers with percentages of 0, 0.7, 1 and 1.5. Then, compressive and tensile stresses, compressive and tensile strains, and compressive and tensile failures were obtained while tunnel lining in the mentioned conditions. Since then, normal and shear stresses and normal and shear displacements of the longitudinal joints of the tunnel were examined. Finally, this paper studied the analytical relationships that existed in the ACI 544.7R-16 regulations and the moment-force diagram for the different percentages of fibers for the joint with the maximum normal stress under earthquake records were compared. Manuscript profile