Abstract

In the emergency repair process of seismic-damaged structures, it is necessary to determine the optimal repair strategy according to damage assessment results, available repair resources and repair time. In this study, the applicable conditions of various member-level and structure-level damage indexes or models are compared. Then, considering the actual conditions of limited available repair resources and repair time in the emergency repair process, the determination method of the optimal imperfect repair strategy is established. On this basis, the determination method of the optimal repair sequence is proposed by taking seismic resilience as the evaluation index. Finally, a seismic fragility analysis method that considers uniform collapse risk and residual service life of structures is introduced, which can be used to analyze the seismic performance of seismic-damaged structures and to compare the repair effectiveness of different repair strategies. Taken a 5-story reinforced concrete structure as an example for analysis. The analysis results show the optimal imperfect repair strategy and the optimal repair sequence determined by the proposed methods can effectively improve the seismic performance of seismic-damaged structures. The fragility analysis results further confirm that the repair based on the optimal imperfect repair strategy can effectively reduce the collapse risk of seismic-damaged structures.

Introduction

A strong earthquake can cause serious damage to engineering structures. The damage or collapse of engineering structures and secondary disasters caused by structural damage or collapse are the main causes of casualties and economic losses [1,2]. After a main shock, it is of great theoretical significance and engineering value to repair seismic-damaged structures according to feasible damage assessment methods and the ideas of seismic performance rapid improvement, so as to reduce the damage degree and collapse risk of seismic-damaged structures under aftershocks, and to reduce casualties and economic losses.

The whole process of performance restoration of seismic-damaged structures includes three important parts: damage assessment, structure repair and retrofit, and seismic performance analysis. In the research on damage assessment, the damage of members can be assessed by damage indexes or models such as maximum drift ratio [3,4], residual drift ratio [5], crack characteristics [[6], [7], [8]], and Park-Ang model [9], and the overall damage of an integral structure system can be comprehensively assessed by deformation-related [10,11] or energy-related [12,13] damage indexes or models. Liu et al. [14] proposed a rapid damage assessment method for reinforced concrete members based on the fractal dimension of cracks, considering the correlation between the fractal characteristics of cracks and the damage state. The reliability of this method was demonstrated through experiments. Tazarv et al. [15] established the relationship between the damage state and deformation of beam and column members, and the computer vision technology was used to quickly detect cracks and failure modes of members, thereby achieving rapid identification of damage state. Makhloof et al. [16] reviewed existing damage assessment methods and emphasized the overall damage assessment methods based on deformation, frequency or modal parameter.

Conclusions

The repair strategy formulated through the damage assessment results of seismic-damaged structures can effectively improve the seismic performance. In this study, the application scope and application condition of different damage indexes or models are compared, the methods for determining the optimal imperfect repair strategy and the optimal repair sequence for seismic-damaged structures under the condition of limited available repair resources is proposed, and a seismic fragility analysis method considering the uniform risk and the residual service life of structures is introduced. Taking a 5-story RC frame structure with a residual service life of 40 years as an example for analysis, the main conclusions obtained from this study are as follows: