Simplified design of bridges for multiple-support earthquake excitation

Savvas P. Papadopoulos*, Anastasios G. Sextos*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

2 Citations (Scopus)

Abstract

This paper presents a novel, bridge-dependent approach for quantifying the increase of design quantities due to spatially variable earthquake ground motion (SVEGM). Contrary to the existing methods for multiple support bridge excitation analysis that are either too complicated to be applied by most practitioners or oversimplied (e.g. Eurocode 8, Annex D provisions), this method aims to strike a balance between simplicity, accuracy and computational efficiency. The method deliberately avoids generating support-dependent, acceleration or displacement, asynchronous inputs for the prediction of bridge response. The reasons behind this decision are twofold: (a) first, the uncertainty associated with the generation of asynchronous motion scenarios, as well as the exact soil properties, stratification and topography is high while, (b) the response of a bridge is particularly sensitive to the above due to the large number of natural modes involved. It is therefore prohibitive to address SVEGM effects deterministically in the framework of a design code. Instead, this new method is based on two important and well-documented observations: (a) that SVEGM is typically globally beneficial but locally detrimental [1], and (b) that the local seismic demand increase is very closely correlated with the excitation of higher modes, which are not normally activated in the case of uniform ground motion [2,3]. Along these lines, a set of static analyses are specified herein to complement the standard, code-based response spectrum analysis. These static analyses apply spatially distributed lateral forces, whose patterns match the shape of potentially excited anti-symmetric modes. The amplitude of those forces is derived as a function of the expected amplification of these modes according to the process initially proposed by Price et al. [4]. Two real bridges with different structural configurations are used as a test-bed to demonstrate the effectiveness of the new method. Comparison of the results with those obtained through rigorous response history analysis using partially correlated, spatially variable, spectrum-compatible input motions [5] shows that, the simplified method presented herein provides a reasonably accurate estimation of the SVEGM impact on the response of the bridges examined at a highly reduced computational cost. This is essentially an elastic method that is found to be simple, yet precise enough to consist an attractive alternative for the design and assessment of long and/or important bridge structures in earthquake-prone regions.

Original languageEnglish
Article number106013
JournalSoil Dynamics and Earthquake Engineering
Volume131
Early online date27 Jan 2020
DOIs
Publication statusPublished - Apr 2020

Keywords

  • Anti-symmetric modes
  • Bridges
  • Multiple-support excitation
  • Seismic codes
  • Spatial variability

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