A New Methodology for Performance-based Seismic Evaluation of Low-rise Reinforced Concrete Buildings Using Nonlinear Required Strengths

Abstract

This study proposes a new methodology based on nonlinear required strengths for evaluating the seismic performance of low-rise reinforced concrete (RC) buildings composed of members controlled by both shear and flexure. The required strengths, which represent the relationships among the strength of members controlled by shear (C_su) and flexure (C_fy) as well as earthquake levels (α) in terms of ductility demand (μ), are equated using regression analysis to estimate α-levels applied to the structure corresponding to μ, C_su, and C_fy. The residual seismic performance (R, damage state) of RC buildings controlled by both shear and flexure is evaluated based on strength capacity in terms of ductility demand by applying the procedure outlined in the Japanese Standard for Damage Level Classification and the Japanese Standard for Seismic Evaluation. We propose a new methodology for performance-based seismic evaluation of low-rise RC buildings with dual lateral-load resisting systems on the basis of the relationships between the R-index and earthquake level evaluated in terms of the ductility ratio. We applied the proposed method to two existing low-rise RC buildings and compared the results to those of nonlinear dynamic analyses where each member was modeled with its flexure spring and shear spring serially connected. We also evaluated the seismic performance of eight actual buildings that suffered damage in the 1995 Hyogoken Nambu and the 1993 Nanseioki earthquakes to demonstrate the effectiveness of this proposed methodology and estimate the degree of damage. Furthermore, we applied the proposed method for seismic evaluation to ten low-rise RC buildings with seismic protection indices of E_S = 0.6, which is the Japanese standard for the critical value required to prevent moderate or greater damage to structures under a rare earthquake with the ground motion acceleration level 0.23g like the 1968 Tokachi-oki EQ and 1978 Miyagiken-oki EQ and to prevent heavy damage under a very rare earthquake with the ground motion acceleration level much higher than 0.23g like 1995 Hyogoken-Nambu EQ. We also compared the relationship between the results of the proposed method and the seismic protection index. The proposed methodology reasonably predicted the earthquake damage sustained by actual buildings, and its results agreed closely with those from detailed nonlinear dynamic analyses and the second-level procedure in the Japanese standard based on E_S = 0.6. The proposed seismic evaluation method was efficient; it provided a means to evaluate the seismic performance considering a specific level of desired structural performance for a specific level of earthquake demand. The new methodology presented in this study can thus be effectively used for performance-based seismic evaluation of low-rise RC buildings composed of members controlled by both shear and flexure.