Assessment of Soil-Structure-Fluid Interaction of a Digester Tank Complex in Liquefiable Soils under Earthquake Loadings

摘要

Evaluating the hydrodynamic effects within a fluid-filled tank during seismic loading is critical for safe design of large fluid-filled tanks. Ideally, a three-dimensional (3-D) numerical model is required to fully capture the dynamic interactions among tank and its support structures, the stored fluid, and foundation soils. However, simulations using a 3-D model may not always be feasible due to project constraints (i.e., costs and schedule) and modeling complexity. This paper presents a case study where an equivalent 2-D tank model was used to capture its 3-D dynamic behaviors so that it can be analyzed using the more-readily available 2-D finite difference computer program FLAC. The cylindrical tank with conical base was modeled using an equivalent 2-D "compression-tension braced frame system" to capture the 3-D tank's ring stiffness. A lumped mass-spring model was also used to represent the hydrodynamic sloshing and impulsive loadings of the stored fluid, and the stiffness of shear walls and secant pile walls on the perimeter of the below-grade reinforced concrete support structure were included in the model. Non-linear plasticity models were utilized to model the non-linear behaviors of the foundation soils, including the PM4SAND effective-stress soil model for the liquefiable soils to estimate the excess pore-water pressure generation under cyclic loading and initiation of liquefaction. The dynamic soil-structure-fluid interaction analysis was performed using seven earthquake motions, selected to represent the design earthquakes for the project. The results show that the simplified 2-D modeling approach using equivalent 3-D structural stiffness can reasonably capture the dynamic responses of this complex fluid-tank system.