青海玛多M7.4地震中野马滩大桥地震动特征初判

2021年5月22日青海省玛多县发生M7.4地震,造成玛多县境内的野马滩大桥和野马滩2号桥发生落梁破坏.中国地震局公布的地震烈度表明野马滩大桥处的地震烈度为Ⅸ.然而野马滩大桥附近无强震台站,未能记录到大桥附近的加速度时程,这也阻碍了野马滩大桥在地震作用下破坏机理的研究.因此,本文尝试采用经验格林函数方法、并参考医学上自身异位皮肤移植的理念,尝试评估野马滩大桥处的地震动的主要特征[包括地震动峰值加速度(PGA)的可能的取值范围和加速度时程],并与已公布的玛多地震的地震烈度、中国地震烈度表(GB/T17742—2020)、第五代地震动区划图(GB18306—2015)中的设计反应谱进行对比.结果表明:(1)本文得到的PGA的取值范围(320~620 cm/s²)与中国地震烈度表(GB/T17742—2020)中地震烈度为Ⅸ区内的PGA的取值范围(402~830 cm/s²)匹配程度较好;(2)本文合成的地震动反应谱与第五代地震动区划图中,野马滩大桥处的极罕遇地震动的加速度设计反应谱整体匹配较好,表明本文合成的加速度时程可以造成野马滩大桥落梁破坏.研究表明本文给出的野马滩大桥附近的地震动强度特征具备一定的参考价值,可作为野马滩大桥处的加速度时程输入,为研究该桥的坍塌机理提供数据支持.

Preliminary judgment of ground motion characteristics of Yematan bridge in Qinghai Maduo M7.4 earthquake

On May 22,2021,an earthquake of M7.4 occurred in Maduo County,Qinghai Province,causing the collapse of the Yematan bridge and the Yematan No.2 bridge in Maduo County.According to the earthquake intensity announced by China Earthquake Administration,the earthquake intensity of the Yematan bridge is IX.However,the lack of strong seismic stations and the unrecorded time history of ground motion near the bridge is also hindering the research work on earthquake-induced failure mechanisms of the Yematan bridge.Therefore,this paper attempts to use the empirical Green's function method and refer to the concept of self-heterotopic skin transplantation in medicine to preliminarily evaluate the main characteristics of the ground motion intensity at the Yematan bridge,and try to give the possible range of peak ground acceleration(PGA)and the ground motion time history.The latest China seismic intensity table(GB/T17742-2020)and the design response spectra of the fifth generation seismic zoning map(GB18306-2015)are compared.The results show that:(1)the range of PGA(320~620 cm/s²)obtained in this paper matches well with the range of PGA(402~830 cm/s²)in China seismic in-tensity table(GB/T17742-2020);(2)The ground motion response spectrum synthesized matches well with the ac-celeration design response spectrum of extremely rare ground motions at the Yematan bridge in the fifth generation seismic zoning map(GB18306-2015),which indicates that the acceleration time history synthesized in this paper can cause the beam falling failure of the bridge.Our results show that the characteristics of ground motion intensity near the Yematan bridge are very possible and have a certain reference value.It can be used as the time history in-put of ground motion for the Yematan bridge and provide data support for the study of the collapse mecha-nism of bridge.