沉管隧道纵向地震易损性分析方法

目前沉管隧道抗震性能设计仅限于横断面分析，缺乏面向沉管隧道纵向抗震性能评估的地震易损性分析方法。为此，建立沉管隧道纵向地震易损性分析方法及评估指标。首先，合理考虑沉管隧道结构特征及接头构造，给出了纵向地震易损性分析模型，其中沉管管节结构采用宏观梁单元模拟，沉管接头采用细观精细化模型模拟，宏-细观模型之间需满足连续性约束方程，地层采用非线性弹簧单元模拟，并通过等效线性化方法来描述地层的非线性特征；其次，根据隧道所处场地的地震动特征选择合适的地震动输入，以及相应的地震动强度指标和结构损伤指标，建立基于增量动力分析的纵向地震易损性评估方法及分析流程，可以依据沉管隧道的不同极限状态定义获得用于纵向抗震性能评估的易损性曲线；最后，以某沉管隧道为应用实例，基于该方法建立了沉管隧道纵向地震易损性分析模型及评估指标，通过计算分析得到了表征隧道纵向抗震性能的地震易损性曲线，并开展多因素分析进而揭示了管节分段长度、地震动输入方向、地层-结构相对刚度比等关键参数的影响规律。结果表明：沉管隧道所处场地位置处的峰值速度是反映隧道纵向地震易损性特征的最优地震动强度参数；沉管隧道地震易损性与输入地震动波长有关，且管节长度与地震波长相近时地震易损性较小；随着地震动输入方向与隧道轴向夹角的增加，沉管隧道地震易损性逐渐减小，而垂直90°输入时相比水平0°输入最大降幅可达76%；地层-结构相对刚度比对沉管隧道纵向地震易损性影响显著，且随地层-结构刚度比的减小而逐渐增大。所提方法可为沉管隧道纵向抗震性能评估及地震风险分析提供科学依据。

Seismic Vulnerability Analysis Method for Longitudinal Response of Immersed Tunnels

The seismic design of immersed tunnels mainly concentrates on cross-sectional analyses, with only a limited number of studies considering longitudinal performance-based seismic design. This paper proposes a longitudinal seismic fragility analysis method and evaluation measures for immersed tunnels. First, the longitudinal seismic fragility analysis method was established by taking the characteristics and joints of immersed tunnels into consideration. The macroscopic beam model was used to simulate an immersed tunnel. The microscopic refinement model was used to capture the dynamic laws of the relative deformation of joints. The soil was simulated using nonlinear spring elements, and the equivalent linearization method was adopted to consider the dynamic nonlinear characteristics. In addition to the selected ground motion, intensity and damage measures were used that corresponded to the dynamic characteristics of the site. The seismic responses were modeled using the nonlinear incremental dynamic analysis procedure. Fragility curves were established at different limit states using an immersed tunnel as an application example. Parametric analyses were performed to investigate the influences of the length of a segment, direction of the earthquake excitation, and soil-structure relative stiffness ratio. The results showed that peak velocity at the tunnel position was the optimal intensity measure for the longitudinal seismic fragility analysis of an immersed tunnel. The seismic fragility was related to the wavelength of the earthquake excitation, and decreased when the length of a segment was similar to the wavelength. The seismic fragility decreased significantly with an increase in the angle between the input direction of earthquake excitation and the axial direction of the tunnel, with a 76% drop when the input direction was 90°. The seismic fragility decreased with an increase in the soil-structure relative stiffness ratio. The proposed method could provide a reference and basis for the seismic risk assessment of immersed tunnels.