Direct estimation of seismic response in reduced‐degree‐of‐freedom isolation and energy dissipation systems

Abstract

Summary A methodology for the development of design tools for direct estimation of peak inelastic response in reduced‐degree‐of‐freedom (RDOF) isolation and energy dissipation systems is presented. The suggested procedure is an extension of an earlier method addressing purely hysteretic isolation systems. Herein, the dynamic equation of motion is first normalised to reduce the number of design parameters that significantly affect the response. The sensitivity of normalised response quantities to the amplitude of the ground motion is then investigated through extensive parametric nonlinear dynamic analyses of isolated single‐degree‐of‐freedom (SDOF) systems with linear viscous damping using code‐based target spectra. Regression analysis is subsequently employed to develop generalised design equations (GDEs) suitable for design. Further investigations are made to address nonlinear viscous damping and the effect of the transverse component of seismic action in two‐degree‐of freedom (2DOF) systems under bidirectional excitation, making the procedure applicable to common bridge isolation schemes. GDEs constitute an alternative to equivalent linearisation approaches commonly adopted by codes, informing the selection among alternative isolation and energy dissipations schemes without requiring iterative analysis. The approach is incorporated in the Deformation‐Based Design methodology for seismically isolated bridges in a forthcoming paper.

Review of annual progress of bridge engineering in 2019

“…The research on seismic isolation system mainly focuses on the simplified calculation method of bridge seismic response and the research of displacement-based seismic isolation design method, mainly adopting the method of theoretical analysis. Gkatzogias and Kappos (2019) proposed a calculation method that can be used to directly estimate the peak inelastic response of isolation and energy dissipation systems with reduced degrees of freedom. Ye et al (2019b) proposed a design method of base-isolated structure based on direct displacement, so that the base-isolated structure with lead-core rubber bearing can meet the performance index specified by the critical displacement value.…”

Deformation‐based design of seismically isolated bridges

“…The shear resistance $${\bar{\nu }}_0$$ represents the ratio V 0 /( mg ), where m is the isolated mass. A near‐optimal isolation solution is defined 8 as one that results in near‐minimum peak total acceleration Ü max of the superstructure while keeping within the allowable limits the peak relative displacements u max of the isolation system and the pier deformations; different approaches can be explored by duly exercising engineering judgement. Both objectives of the preliminary design can be investigated either on the basis of an elastic (response spectrum) analysis by introducing an iterative equivalent linearisation technique (e.g., 14 ), or by using GDEs 8 .…”

“…Considering multiple performance levels and different performance objectives, the proposed method for isolated bridges initially identifies the critical hazard level and “near‐optimal” alternatives of the isolation system in terms of both performance and economy. To this end, it integrates generalised design equations (GDEs), a novel design tool 8 developed by the authors for the direct estimation of inelastic response in RDOF isolation and energy dissipation systems without the need for iterative structural analysis. The isolation and energy dissipation scheme is realised by selecting devices (type and mechanical properties) that result in the adopted near‐optimal response.…”

Simple and Complex Modelling of Seat-Type Abutment-Backfill Systems

“…The nonlinear dynamic response of the bridge was studied to better understand its overall dynamic behaviour and to identify modelling issues that should be further addressed. For the dynamic response history analysis, the bridge is subjected to a set of artificial accelerograms scaled to various levels of intensity, multiples of the design seismic action (0.16g, 0.32g and 0.48g, considering soil class C according to Eurocode 8, but assuming that TD = 4s instead of TD = 2s suggested by EC8, as a more representative value of high seismicity regions [21], [22]). In the longitudinal direction, 3 pairs of nonlinear spring and dashpots are used to represent the backfill, while in both directions separate gap elements are used.…”