Displacement Reduction Factors for the Design of Medium and Long Period Structures

Abstract

The estimation of the maximum inelastic displacement response of structures is gaining increasing importance with the development and application of the so-called “Performance-Based Design” (PBD) procedures, in which important performance criteria are directly correlated to the seismic displacement demand. The maximum displacement of a MDOF structure is often estimated using the “equivalent SDOF system” concept, which reduces the problem to the prediction of the maximum inelastic displacement demand of an equivalent SDOF system with characteristics representative of the MDOF structure. This study focuses on the nonlinear response of SDOF systems with medium and long periods (T > 1 s), typical of tall buildings for which PBD is more widely adopted. In particular, the effect of several characteristics on the nonlinear response of the equivalent SDOF is investigated, such as structural period, ground motion spectral shape, sensitivity of spectral shape to damping, and elastic damping ratio. Design equations for the prediction of the max SDOF inelastic displacement accounting for all the identified influencing parameters, and based on the newly introduced Displacement Reduction Factor (DRF) concept, are proposed.