A New Method for Defining the Optimal Separation Gap Distance and the Acceptable Structural Pounding Risk on Multistory RC Structures

A proposal to control the structural pounding hazard imposed on multistory reinforced concrete (RC) structures is presented. The main goal is to guarantee the seismic performance of a structure with an acceptable (predefined) risk-targeted parameter without the need to eliminate structural pounding collisions. The key target parameters of this study are the annual probability of exceeding an engineering demand parameter (EDP) capacity level and the separation distance d_g between adjacent structures. In this direction, a method that ensures the performance level of critical EDPs due to structural pounding conditions is proposed. The new method involves two decision frameworks that define (a) the optimal separation gap distance $\left({\mathrm{d}}_{\mathrm{g},\mathrm{m}\mathrm{i}\mathrm{n}}^{{\mathrm{P}}_{\mathrm{t}}}\right)$ at a targeted value of pounding risk (probability per year) P_t (Decision A) and (b) the minimum acceptable structural pounding risk ${\mathrm{P}}_{\mathrm{m}\mathrm{i}\mathrm{n}}^{{\mathrm{d}}_{\mathrm{g},\mathrm{t}}}$ at a targeted value of separation gap distance d_g,t (Decision B). The demand parameters that are incorporated in the proposed method are the peak relative displacement δ_max at the top level of colliding without considering pounding conditions and any other critical EDP due to the structural pounding effect. The overall method is based on two distinct acceptable performance objectives, the POs-δ_max and the POs-EDP, defined as a function of P vs. d_g. For this purpose, a seismic hazard curve compatible with Eurocode’s 8 hazard zone is adopted, and the corresponding demand hazard curves of δ_max and EDP are developed. The proposed method is implemented to study the floor-to-floor structural pounding hazard of an eight-story RC frame taking into account different risk-targeted scenarios. The results show that the seismic risk (probability per year) of exceeding the EDP’s capacity level is significantly increased due to structural pounding in comparison to the case of no pounding. Calibration of the structural pounding risk can be obtained by adjusting the separation gap distance d_g between the adjacent structures based on the acceptable POs. The POs-δ_max is not always an accurate criterion for verifying the capacity level of the critical EDP. Finally, with the proposed method, a variety of POs-EDPs can be used to control the structural pounding risk in terms of ${\mathrm{d}}_{\mathrm{g},\mathrm{m}\mathrm{i}\mathrm{n}}^{{\mathrm{P}}_{\mathrm{t}}}$ and/or ${\mathrm{P}}_{\mathrm{m}\mathrm{i}\mathrm{n}}^{{\mathrm{d}}_{\mathrm{g},\mathrm{t}}}$.