Analysis of characteristics of ground motion and typical bridge performance in the Baoshan earthquake

Abstract

A Ms5.2 earthquake occurred in Longyang District, Baoshan City, Yunnan Province on 2 May 2023. The earthquake caused some degree of damage to power facilities and roads. Since then, small and medium sized earthquakes have occurred frequently in this region. In order to better analyze the characteristics of ground motion in this area and the coping strategies of related bridges, the response spectra, omnidirectional response spectra and omnidirectional representations of other indexes of intensity measure from records of strong ground motion were analyzed using the seismic records recorded by stations near the epicenter. Four typical bridges near the epicenter were selected for modeling and seismic response analysis to derive their damages under the action of ground motion, and structural displacements of the bridges with the strong ground motion were compared to analyze directional linkages. The Incremental Dynamic Analysis (IDA) method was used to analyze the fragility of the four bridges, and the seismic capacity of different bridges under the ground motion was compared. The omnidirectional displacement response spectra of the two stations and the omnidirectional representations of other indexes of intensity measure have obvious directionality, and the predominant direction is perpendicular to the direction of the fault, reflecting the rupture directionality of the earthquake. Comparing the corresponding period of the structural displacement response with seismic action with the omnidirectional displacement response spectra, it was found that the bridge structural displacement is correlated with the predominant cycle and predominant direction of the omnidirectional displacement response spectra. Under the same seismic action, the maximum moment of the deck arch bridge in the transverse direction is larger than that in the bridge direction; the larger the span of the deck arch bridge, the larger the maximum moment at the arch footing. According to the analysis of fragility, it can be seen that the seismic capacity of the continuous rigid frame bridge is much lower than that of the deck steel truss arch bridge under this ground motion. Compared to the deck-type concrete arch bridge, the deck steel truss arch bridge has greater seismic capacity. In this paper, based on the structural analysis and fragility analysis of these four bridges close to the fault, the structural damage and damage levels in the future earthquake are speculated, which provide suggestions for the follow-up maintenance and reinforcement work, and are also conducive to the resilience evaluation and rapid repair work after the real earthquake damage.