An improved CWT-based algorithm for the generation of spectrum-compatible records

Luis A Montejo,Luis E Suarez

doi:10.1186/2008-6695-5-26

Abstract

The seismic design of most civil structures is usually accomplished using the response spectrum approach or simplified equivalent lateral force methods. However, some special tasks require the use of dynamic time history analyses. In the nuclear industry, for example, dynamic analyses are required in the design verification and seismic assessment of critical buildings and in the development of floor response spectra and free-field ground response spectra. The input motion for these analyses requires acceleration time series whose response spectrum matches a target design spectrum. This article revises the continuous wavelet transform (CWT) approach to generate spectrum-compatible records from the modification of acceleration time histories recorded in actual seismic events. The computational efficiency of the algorithm is increased greatly by performing the wavelet decomposition and details reconstruction via fast convolution using fast Fourier transforms. The new algorithm is evaluated using a typical design spectrum from the nuclear industry and different seed records.

Highlights

Independent of the approach selected, either displacement or force-based, most of the seismic designs of civil structures are performed using variations of the response spectrum method, where the ground motion is represented as a design response spectrum that is representative of the seismic hazard on the site
CWT-based methodology for the generation of spectrum-compatible records For completeness, this section briefly describes the methodology to manipulate historic earthquake records to obtain spectrum-compatible accelerograms based on the continuous wavelet transform (CWT)
Since the scale s can be related to frequency, the CWT is occasionally used in earthquake engineering to obtain simultaneous time-frequency representations of earthquake records (e.g., Montejo and Kowalsky 2008)

Summary

Introduction

Independent of the approach selected, either displacement or force-based, most of the seismic designs of civil structures are performed using variations of the response spectrum method, where the ground motion is represented as a design response spectrum that is representative of the seismic hazard on the site. The (pseudoaccelerations or relative displacements) design response spectrum is used to estimate the force or deformation demand imposed on the structure. For some special tasks or structures, dynamic time history analyses are required. In the standard American Society of Civil Engineers (ASCE) 7–10, for example, if the structure meets the characteristics necessary to be considered as irregular, dynamic analyses (either modal response spectrum or time history) are required to verify the design of the structure. Dynamic time history analyses are required in the design, verification, and seismic assessment of critical buildings.

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Conclusion