## 6 Summary and Conclusions  
Prior numerical and analytical studies have documented the necessity of addressing the joint effect on seismic performance for underground structures with abrupt stiffness changes. However, the above models have yet to be validated by experiments due to the lack of laboratory data. As part of the ongoing Shanghai Metro-funded research project, aiming at a better understanding of the seismic behavior of the cross interchange station and developing rational design methods, the presented paper focused on the large-scale shaking table study. A series of large-scale (1 g) shaking table tests were conducted at Tongji University, using synthetic model soil (a mixture of sawdust and dry sand) and granular concrete with steel wires to model the soil-structure system. An experimental comparative study of the interchange station was carried out in reference to a single station under sinusoidal seismic excitations. The key conclusions can be summarized as follows:  
* The horizontal accelerations recorded in the four soil arrays near the interchange station were found to vary based on their relative locations from the structure, indicating the spatial effects of the interchange station on the near-structure soil;  
Figure 15: Time history of the bending moment at the top end of the column of the upper story, derived from the strain pair records: a comparison between the single station and different sections of interchange station in the case of four sine sweep cases. It was found to be consistent in the interchange station and the single station that the horizontal acceleration recorded on the elevation of the top slab was higher than that of the bottom slab. Though subjected to uniform transverse excitations, the conjunction and the two-story section of the interchange station responded differently, as revealed by the horizontal acceleration data;
* The time histories of the dynamic longitudinal strain pairs recorded at the two sides of the cross-section were found to be 180 degrees out of phase. This indicated the deflection of the longitudinal axis of the two-story section under transversal motions, which was caused by the discrepant response. The longitudinal strain was distinctly raised near the conjunction, where special attention should be paid to seismic design;
* The bending moment of the column in the two-story part of the interchange station was affected by its rigid conjunction to the three-story part. The columns recorded a greater bending moment in _section 5_, which was further from the conjunction, compared with the closer one (_section 3_). The presence of the conjunction also induced a lower column moment in the interchange station compared with those in the single station. This paper provides experimental insights into the seismic response of a typical cross interchange station. However, a number of factors could affect the station-conjunction-soil interaction, including relative soil-station stiffness, soil-structure interface behaviors and input motions. After being calibrated against the experiments, further numerical analysis is needed to shed light on the sophisticated response of the interchange station. Numerical simulation in accord with the experiment conditions, as well as a comprehensive investigation, will be presented in another upcoming paper. Conceptualization, S.G.; methodology, Y.Y. and W.W.; software, W.W.; validation, Y.Y. ; formal analysis, W.W.; investigation, W.W.; resources, S.G., W.D. and Y.Y. ; data curation, W.W.; writing--original draft preparation, W.W.; writing--review and editing, Y.Y., W.D. and S.G.; visualization, W.W.; supervision, S.G., Y.Y. and W.D. ; project administration, Y.Y. ; funding acquisition, S.G., Y.Y. and W.D. All authors have read and agreed to the published version of the manuscript. The authors express their gratitude for the financial support from the National Natural Science Foundation of China (51478343 & 51778487& 52061135112) and the Shanghai Metro Research Project (JS-KY17R031-6). Not applicable.