Evaluation of Reduction Factor for concrete coatings of underground structures under blast loading

In general, underground structures exhibit nonlinear behavior when applying dynamic loads such as earthquakes and explosions. One of the most important parameters for loading, analyzing and designing this type of structures is the dynamic load factor of the behavior coefficient. This coefficient contributes to the nonlinear behavior of the structure in linear analysis, or in other words, is a factor affecting the nonlinear behavior of the structure in linear analysis. By applying this coefficient, linear analyzes can replace conventional nonlinear analyzes in the analysis and design of explosive-proof structures, which are mostly time-consuming and complex. Investigations show that the acceptable amount or range for reduction factor of concrete coating of underground structures under the influence of explosive loads is not determined totally. To find this factor, the tunnel structure must first be modeled by a software that is able to calculate the interaction between the structure and the soil. In this research, plastic hinges were introduced into the SAP2000 software, and a pushover analysis was carried out on a concrete coating of a tunnel under an explosive charge pattern By output of this analysis, the force-vertical displacement diagrams is plotted for each of the tunnel performance levels and the Reduction Factor is obtained for pattern of explosive charge by using the relationships that explained in paper. It can be seen that the Reduction Factor for such structures depends only on the two parameters of ductility and over strength of structure.