Optimal yield level of bilinear seismic isolation devices

Abstract

SUMMARYThe yield level of an insulator is one of the important parameters which are related to responses and absorbing energy under seismic input energy in isolated structures. The purpose of this paper is to determine the optimal ratios of yield force of the isolator (Q ) to the total weight of the structures (=). To obtain the optimal ratio, 1044 two-degree-of-freedom isolated bridge models, which have bilinear isolators, were selected. These 2-DOF isolated bridge models with superstructure isolation can consider pier #exibility and various parameters of the isolator. Two formulas for determining the optimal yield ratio are proposed and compared with the previous researches. RAE (the ratio of absorbed energy by the isolator to the total input energy) is related directly to structural responses, and Optimal Yield Ratio (OYR), de"ned as a yield ratio at maximum RAE, can be obtained from the relationship between RAE and Q /=. Here, we found that RAE is a reliable factor to evaluate OYR, and it is proportional to earthquake amplitudes under the same kinds of earthquake loadings. Using the proposed formulas, OYR is determined and the optimal yield force of the isolator can be obtained easily and reliably at a seismic isolation design stage.

Effect of lead rubber bearing characteristics on the response of seismic-isolated bridges

“…It is largely related to structural responses and the absorbing energy of isolators under earthquake loadings (Park and Otsuka, 1999). The yield strength of the isolator is associated with the characteristic strength by the relation,…”

“…Skinner et al (1999) suggested typical value of Q d /W = 0.05 and K u /K d = 1/5 to 1/6 for moderate earthquakes. Park and Otsuka (1999) compared different method to determine the yield ratio and recommended Q d / W = 0.43 to 0.5 for moderate earthquakes. Naeim and Kelly (1999) has given the design recommendation for K u /K d = 1/10.…”

Application and design of lead-core base isolation for reducing structural demands in short stiff and tall steel buildings and highway bridges subjected to near-field ground motions

“…The LCR isolator was redesigned with a new value of Q total [Inaudi and Kelly 1993], following the ground excitation,ẍ g . Park and Otsuka [1999] suggested that the optimal range of Q total be between 14% to 18% of the total weight of the building in order to achieve adequate seismic isolation and control building responses under severe ground motion. Spencer et al [2000] further suggest that Q total be selected between 13% to 17% of the total building weight and to select the stiffness ratio, B ratio , to be approximately 10 in order to significantly reduce base drifts and moderate the acceleration responses for buildings subjected to severe ground motions.…”

Evaluation of Approaches to Characterize Seismic Isolation Systems for Design

“…Several researchers have explored the application of nonlinear response spectrum approaches for isolation systems [Park and Otsuka, 1999;Ryan and Chopra, 2004;TenaColunga, 2002;Zhao and Zhang, 2004]. Ryan and Chopra [2004] developed an approach that characterizes the isolation system according to the period corresponding to its post-yield stiffness and the yield strength normalized by peak ground velocity.…”

“…As a drawback, the normalized strength is not an effective measure of the energy dissipation capacity of the system. In Park and Otsuka [1999], a method was developed to determine the optimum yield strength of an isolation system based on the absorbed energy and total input energy to the system, which is dependent on ground motion intensity.…”