The underground structure with stiffness mutation at the culvert-frame connection suffers from discrepant dynamic responses when earthquakes strike.This paper studies the seismic responses of an underground structure consisting of two portions of box frames and twin jacked culverts in soft soil.The two portions of box frames(Part A and Part C)have the same 2-storey and 3-span cross sections,rigidly connected to the two parallel jacked culverts(Part B)with F-type sockets between joints.A series of 1g shaking table tests is conducted on the modeled soil−structure system.Accelerometers are installed within the model soil,upon culverts,and on the top of mid slabs of box frames.Joint extensions and closures of culverts are measured.The white noise case is carried out to assess dynamic characteristics of the model system.Four synthetic earthquake cases are conducted to investigate the model system’s seismic responses under earthquakes with varying intensities.Ground acceleration responses of the model soil at different distances from Part A are compared.The extent of discrepancy in acceleration of culverts and box frames is quantified by the correlation coefficient.The characteristics of the joint extension and closure are summarized.
