考虑海底地震动作用的跨海斜拉桥抗震韧性评估

Assessment on Seismic Toughness of Cross-sea Cable-stayed Bridges Considering Effect of Offshore Ground Motion

摘要:

海床场地存在淤泥软土层和海水层，导致海底地震作用不同于陆地地震作用。为研究海底地震作用下跨海斜拉桥抗震性能，以一座典型的双塔斜拉桥为例，对两类地震动作用下的桥梁抗震韧性进行分析。首先构建了桥梁抗震韧性分析方法。随后，从K-NET台网的强震数据库分别选取了83条海底和陆地强震记录，对比了两类地震动放大系数谱的特征及差异。然后，通过非线性时程分析研究了斜拉桥各构件的地震响应特征，确定了构件最不利位置。在此基础上，结合各构件地震损伤指标，对斜拉桥地震损伤概率及抗震韧性开展研究。结果表明：受结构周期影响，海底地震动放大系数谱值可能大于或小于陆地地震动。斜拉桥主塔的薄弱位置位于塔底，最易损的拉索是连接辅助墩的拉索，塔梁连接处的主梁是最危险截面；较陆地地震动而言，海底地震动下的斜拉桥地震损伤概率明显偏高、抗震韧性偏低，最大差异为40%和11%。跨海斜拉桥采用陆地地震动进行抗震分析可能存在低估地震损伤概率、高估抗震韧性的风险。

Abstract:

There are silt-soft soil layers and seawater layers in the seabed, which cause the offshore seismic action to be different from that on land. To study the seismic performance of cross-sea cable-stayed bridges under the action of offshore earthquakes, taking a typical double-pylon cable-stayed bridge as an example, the seismic toughness of bridges under two types of ground motion is analyzed. Firstly, the seismic toughness analysis method of bridges is established. Secondly, 83 records of offshore and onshore strong earthquakes are selected respectively from the strong earthquake database of the K-NET network to compare the characteristics and differences of the two types of ground motion amplification coefficient spectra. And then, the seismic response characteristics of each component of the cable-stayed bridge are studied through nonlinear time-history analysis, and the most unfavorable positions of the components are determined. On this basis, the seismic damage probability and seismic toughness of the bridge are studied in combination with the seismic damage indicators of components. The results show that the spectral value of the amplification coefficient of offshore ground motion may be greater than or less than that of onshore ground motion due to the influence of the structural period. The vulnerable section of the main pylon of the cable-stayed bridge is located at the bottom of pylon, and the most vulnerable stayed cables are those connecting the auxiliary piers. The girder at the connection between the pylon and girder is the most dangerous section. Compared with onshore ground motion, the probability of seismic damage to cable-stayed bridges under offshore ground motion is significantly higher, while the seismic toughness is relatively lower, and the maximum differences is 40% and 11% respectively. The seismic analysis of cross-sea cable-stayed bridges using onshore ground motion may carry the risk of underestimating the probability of seismic damage and overestimating seismic toughness.