Vertical Seismic Effect on the Seismic Fragility of Large-Space Underground Structures

Zhiming He,Qingjun Chen

doi:10.1155/2019/9650294

Abstract

The measured vertical peak ground acceleration was larger than the horizontal peak ground acceleration. It is essential to consider the vertical seismic effect in seismic fragility evaluation of large-space underground structures. In this research, an approach is presented to construct fragility curves of large-space underground structures considering the vertical seismic effect. In seismic capacity, the soil-underground structure pushover analysis method which considers the vertical seismic loading is used to obtain the capacity curve of central columns. The thresholds of performance levels are quantified through a load-drift backbone curve model. In seismic demand, it is evaluated through incremental dynamic analysis (IDA) method under the excitation of horizontal and vertical acceleration, and the soil-structure-interaction and ground motion characteristics are also considered. The IDA results are compared in terms of peak ground acceleration and peak ground velocity. To construct the fragility curves, the evolutions of performance index versus the increasing earthquake intensity are performed, considering related uncertainties. The result indicates that if we ignore the vertical seismic effect to the fragility assessment of large-space underground structures, the exceedance probabilities of damage of large-space underground structures will be underestimated, which will result in an unfavorable assessment result.

Highlights

Large-space underground structures such as subway stations, commercial streets, and parking lots are wildly used urban construction measures. ese structures can suffer severe damage under strong ground shaking [1, 2]
The soil-underground structure pushover analysis method which considers the vertical seismic loading is applied to obtain the performance index thresholds. It is evaluated through incremental dynamic analysis method under the excitation of horizontal and vertical acceleration, the soil-structure-interaction and ground motion characteristics are considered
In order to determine the thresholds of different performance levels based on pushover analysis results, in this study, lateral load-drift curve (Figure 11) is adopted as the backbone curve model based on the experimental study [49]. is model consists of four performance levels for the component, which are in accordance with the definition of performance levels in this study

Summary

Introduction

Large-space underground structures such as subway stations, commercial streets, and parking lots are wildly used urban construction measures. ese structures can suffer severe damage under strong ground shaking [1, 2]. It has been proved that the contribution of vertical earthquake component is one of the major factors to the failure of the structure [7, 8, 14,15,16] Both Parra-Montesinos [7] and Iida et al [12] verified that the high axial load induced by the vertical component of ground motion can increase the axial compression ratio and reduce the ductility of central column of large-space underground structures, which is one of the most important factors of collapsing. The soil-underground structure pushover analysis method which considers the vertical seismic loading is applied to obtain the performance index thresholds In seismic demand, it is evaluated through incremental dynamic analysis method under the excitation of horizontal and vertical acceleration, the soil-structure-interaction and ground motion characteristics are considered. To construct the fragility curves, the evolutions of performance index versus the increasing earthquake intensity are performed, considering related uncertainties

Methodology

Case Study

Findings

Conclusions