Seismic isolation analysis of integrated aqueduct considering soil-structure interaction and topographic effect
HAN Zhongqi1, Ao Xuannian2, JIANG Jibin2, WANG Haishen1, PAN Peng1,3
1. Department of Civil Engineering, Tsinghua University, Beijing 100084, China; 2. Central Yunnan Water Diversion Engineering Co., Ltd., Kunming 650000, China; 3. Key Laboratory of Civil Engineering Safety and Durability of Ministry of Education of China, Tsinghua University, Beijing 100084, China
Abstract：[Objective] An aqueduct is a simply supported bridge-like structure whose main purpose is to transport water over long-distance and difficult terrains. When an aqueduct is constructed in seismically active regions, base-isolation is often needed. However, current research on aqueducts that considers both the pier-soil interaction and topographic effects is lacking. This paper theoretically analysis the influences of pier-soil interaction and topographic effects (mainly V-shaped canyon effect) on the base-isolated Songlin aqueduct of Central Yunnan Water Division Project during an earthquake event. [Methods] The analysis is achieved through modelling using the universal large-scale finite element analysis (FEA) software ABAQUS. The soil-structure interaction (SSI) is simulated through m-method and the equal-stiffness pier method according to relevant standard and research, respectively. The m-method simplifies the SSI as a series of springs. The stiffness of each spring is related to the pier geometries and soil thickness considered. The fluid-structure interaction is simulated through simplified spring-mass model, which is a commonly used analytical model to simulate fluid-structure interaction. In this paper, the spring-mass model is modified for computational efficiency. The results of the modified and traditional spring-mass model are compared to verify the effectiveness of the modified model. The FEA model mainly consists of beam elements and the popular user-defined material database PQ-fiber is adopted in the analysis. Post-tensioning of the aqueduct is achieved through temperature-gradient and material expansion coefficient in ABAQUS. Three-dimensional earthquake actions selected from PEER database are inputted at the pier base of the model as accelerations to simulate the dynamic structural responses of the aqueduct. The V-shaped canyon effect is considered by transforming the time-history and peak ground acceleration (PGA) of the earthquake records. [Results] The structure periods of aqueduct were 2.81, 1.72 and 1.40 s for the first three deformation modes, respectively. The structure periods changed to 2.82, 1.75 and 1.44 s after the introduction of SSI, respectively. The FEA results indicated that the pier deformation, inter-span relative displacement and isolation bearing deformation were amplified after SSI was introduced. Amongst the parameters, the deformation of the isolation bearings was observed to approach its design limits. This posed the threats of isolation bearing failure during a seismic event. The flexure strength demands at the base of the piers are relatively insensitive to the introduction of SSI. It was also found that the higher the pier, the effects of SSI on inter-span relative displacement, isolation bearing deformation and pier-base flexural strength demand became more pronounced. [Conclusions] the introduction of SSI decreased the stiffness of pier-ground connection which resulted in the slight decrease of the structural period of the aqueduct. Parametric analysis of the angles of incidence between the horizontal surface and the horizontally-polarized shear waves produced due to V-shaped canyon effect demonstrated that the overall response of the Songlin aqueduct is greatest with the horizontal incidence, followed by the oblique incidence, uniform incidence and vertical incidence. It is also found that the inter-span relative displacement and isolation bearing deformation along the aqueduct direction can exceed their respective design limits and should be carefully checked in the design process.
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2024, Vol. 64 
