Seismic response analysis of large-scale base-isolated LNG tanks on non-bedrock sites under obliquely incident SV waves

Objective For large-scale LNG tanks constructed on non-bedrock sites in practical engineering, a structural system combining pile-group foundations and isolation bearings is commonly adopted. Under seismic excitation, the coupling of site nonlinearity, pile-soil dynamic interaction, hysteretic energy dissipation of isolation bearings, and spatial propagation effects of seismic waves leads to more complex dynamic responses compared with tanks on bedrock sites. Most existing studies adopt the assumption of vertical uniform seismic wave input, which cannot reflect the propagation time and spatial phase differences at large-diameter tank foundations under obliquely incident seismic waves.

Methods Focusing on a planned 22 × 10⁴ m³ concrete full-containment LNG tank on a non-bedrock site in China, this study establishes a three-dimensional integrated finite element model that incorporates multi-layer site soils, 379 piles in the pile group, elevated pile cap, LRB900 lead-rubber isolation bearings, and inner-tank and outer-tank structures. Soil nonlinearity is captured via equivalent linearization, while oblique Shear Vertical (SV) wave inputs are applied using the boundary-substructure method. Three real strong-motion records with distinct spectral characteristics are selected and uniformly scaled to a peak ground acceleration of 2.36 m/s². Key seismic responses of the tank and pile foundation are compared and analyzed under incident angles of 30°, 45°, 60°, and 90° (vertical incidence).

Results Results indicate that oblique wave incidence induces non-uniform seismic input across the foundation, driving coupled horizontal translation and global rotation of the tank. Compared to vertical incidence, the peak tank-wall acceleration shifts from the mid-height toward the dome. Internal force variations across incident angles stem from the coupling between multiple reflections and transmissions of SV waves in layered soils and site nonlinearity, peaking at a 30° incidence angle. Driven by the mechanical properties of isolation bearings, relative displacement at peak tank-wall displacement varies non-monotonically with incident angle. Nevertheless, under the same seismic record, peak tank-wall displacements at various incident angles stay within the allowable design limits of the tank structure.

Conclusion For large-scale LNG tanks on non-bedrock sites, seismic analysis and design should account for oblique wave incidence and spatially non-uniform foundation input as important influencing factors. Comprehensive identification of unfavorable responses of the tank and pile-group foundation requires evaluating ground motions across diverse spectral characteristics and incident angles. These findings provide references for seismic performance evaluation, critical response identification, and design optimization of base-isolated LNG tanks on non-bedrock sites.