Multidimensional Fragility Analysis for a NEES Frame Structure by Integrating a New Energy Damage Index: Cumulative Plastic Strain

Qiang Wang,Ziyan Wu

doi:10.1155/2019/7323656

Abstract

Cumulative plastic strain (CPS) damage index is proposed in this study for seismic fragility analysis by integrating the force analogy method into the energy balance equation, and CPS can be defined as the ratio of the demand of plastic dissipation energy to its capacity. The cumulative plastic strain can indicate the structural damage cumulative effect under earthquakes, which makes it especially suitable to be selected as the damage index for the structural component. Threshold values of cumulative plastic strain for different performance limit state (PLS) levels are obtained through the degree of consistency of interstory drift-based fragility curves and CPS-based fragility curves. Regarding the multidimensional fragility evaluation, CPS and the floor acceleration will be selected as the quantification indices for performance limit state of the structural component and nonstructural component, respectively. The probabilistic seismic demand model (PSDM) following multivariate logarithmic normal distribution will be developed, and taking PLS uncertainty and correlation into consideration, multidimensional PLS function is constructed to identify the structural failure domain. A full-scale 2-bay 2-story frame structure for the Network for Earthquake Engineering Simulation (NEES) project is employed as the case study structure to demonstrate the proposed theory. Nonlinear dynamic time-history analysis is carried out for the structure to obtain its maximum responses under earthquakes. Consequently, the multidimensional fragility curves can be derived on the basis of CPS. Besides, the influence of PLS threshold value, engineering demand parameter (EDP) correlation, and PLS correlation on the multidimensional fragility is investigated. Results show that (1) CPS damage index can fully consider the cumulative effect of damage under earthquakes, which makes up for the deficiency of the interstory drift damage index in this aspect, (2) the multidimensional fragility framework can deal with the PLS correlation and EDP correlation simultaneously, which will generate a more precise seismic damage assessment result, and (3) multidimensional fragility is sensitive to PLS threshold values and PLS correlation parameters.

Highlights

Extensive damage to engineering structures under earthquakes highlighted the vulnerability of structures to seismic excitation
In the framework of performance-based earthquake engineering, the degree of structural damage is quantified and the system performance levels are classified as different states, e.g., fully operational, life safety, and near collapse
Considerable efforts have been devoted to the selection structural damage accumulation effect under earthquakes of the damage index

Summary

Introduction

Extensive damage to engineering structures under earthquakes highlighted the vulnerability of structures to seismic excitation. Lv and Wang [7] proposed a decisionmaking method of the optimal seismic fortification level for aseismic structures based on damage performance. Ding et al [8] considered the damage accumulation and the strain reinforcement effect of the steel and established the damage mechanics model for the steel structure based on. T structure under earthquakes and proposed a new ductility damage index for the bridge piers. Diaz et al [17] developed a damage plastic strain, was proposed for the structural component by using plastic dissipation energy and it can consider effects of the damage caused by repeated cycles under earthquakes. Within the framework of multidimensional fragility theory, engineering demand parameters (EDPs), respectively, for the structural and nonstructural component are selected to construct multidimensional probabilistic seismic demand model and multidimensional PLS function. The sensitivity of multidimensional fragility with regard to acceleration threshold and performance limit state correlation is investigated to reveal their influence on the failure probability

Research Significance

Cumulative Plastic Strain Based on Plastic Dissipation Energy

E Three-dimensional PLS surface

E Figure 6

E Ni: Correlation coefficient