## 7 Conclusions  
A series of large-scale shaking table tests were conducted to study the seismic performance of the culvert-frame combined underground structure under longitudinal and transverse earthquake excitations. Owing to the culvert-frame interaction and the soil-structure interaction, discrepant responses of the model structure and model soil under the longitudinal and transverse earthquake excitations were detected. The following conclusions are drawn. Figure 14: Culvert joint deformations in longitudinal and transverse cases of SEM-0.2g at (**a**) maximums of transducers OJ1-OJ40, (**b**) maximums of transducers IJ1-IJ40, (**c**) maximums of transducers IJ41-IJ80, and (**d**) maximums of transducers OJ41-OJ80. 1. The ground surface exhibits the same dominant frequency but different amplitudes under the longitudinal and transverse excitation in the WN case. From both time and frequency domain perspectives, the acceleration responses of the model soil are greater under transverse excitations than under longitudinal excitations. 2. Under transverse excitations, different floors of the frames (Part A and Part B) have more consistent peak accelerations than those under longitudinal excitation. The longitudinal excitations enlarge the acceleration component in the frequency range of 8 Hz to 12 Hz compared with the transverse excitations. 3. The peak accelerations of culverts increase from the end near Part A to the end near Part C under longitudinal excitations. The peak accelerations in the center of the culvert are significantly greater than those at both ends under transverse excitations. Moreover, correlation coefficients of the accelerograms statistically quantify the discrepant acceleration responses in the center of the culvert under transverse excitations. The acceleration component in the frequency range of 8 Hz to 12 Hz under longitudinal excitations is greater than that under transverse excitations. 4. The distribution of culvert joint deformations is spiky, i.e., several culvert joints have deformations much larger than the average value. The culvert joint deformations are greater under longitudinal excitations than under transverse excitations. The spiky culvert joint deformations tend to occur at the ends of culverts under transverse excitations, while there is no significant trend of spiky deformation locations under longitudinal excitations. The joints at culvert ends have greater deformations because the frames' restrained effect on the culverts is negatively correlated to the distance. The enhancement of the joints at culvert ends is necessary. The discussions in this paper are mainly qualitative descriptions based on the raw data and primarily processed data. It would be expected that more quantitative and theoretical conclusions might be generated through future studies. The model culvert and model frame are connected by combining epoxy resin and carbon fiber cloth, which can be considered a rigid culvert-frame connection. Seismic performances of culvert-frame underground structures with flexible culvert-frame connections will be discussed in future work. Data curation, X.L. and W.W.; formal analysis, W.W. and X.W. ; investigation, X.L. and X.W. ; project administration, Y.Y. ; visualization, X.L. ; writing--original draft preparation, Y.Y. and X.L. ; writing--review and editing, Y.Y. and X.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the Science and Technology Commission of Shanghai Municipality (No. 22 DZ1203005 and No. 23 DZ1202906) and Shanghai Sailing Program (23 YF1440500). Not applicable. The data used to support the findings of this study are available from the corresponding author upon request. Authors [PERSON] and [PERSON] were employed by Shanghai Tongji Green Building Prefabrication Construction Engineering Technology Co., Ltd. Author [PERSON] was employed by Shanghai Tunnel Engineering & Rail Transit Design and Research Institute. Author [PERSON] was employed by Shanghai Shentong Metro Construction Group Co., Ltd.