Research on seismic analysis methods of large and complex underground pipe structures in hard rock sites

In order to study the seismic design methods of large and complex underground pipe structures (LCUP) in hard rock sites, firstly, the structural characteristics of LCUP and the calculation principles of four typical seismic analysis methods were carefully sorted out. Secondly, based on different seismic analysis methods, the deformation and internal force response of three representative pipes were studied in detail, and the calculation accuracy and error causes of each seismic analysis method were analyzed. Finally, the advantages, disadvantages and applicability of the seismic analysis methods on typical pipes were systematically explained, and the technical route for seismic design of LCUP was proposed. The results showed that both the reaction displacement method and the reaction acceleration method can effectively analyze the seismic performance of standard section structures. The three-dimensional time-history analysis method was comprehensive and highly accurate for seismic analysis of complex spatial cross-node structures. The rigid connections of different pipes leaded to serious discontinuities in stiffness at the intersection, and the deformation and bending moment distributions were highly concentrated at the height away from the intersection. The influence range of the intersection was about three times the width of the intersection, and LCUP was classified according to this influence range. For standard section structures, seismic analysis should be carried out using the reaction acceleration method or reaction displacement method, while for spatial cross-node structures, three-dimensional time-history analysis should be used for seismic analysis. This scientific seismic design method achieved multiple optimal balances of seismic safety, analysis accuracy, efficiency and economy in the seismic analysis of large and complex underground structures. A theoretical basis and useful reference for the scientific design, accurate prediction and seismic safety evaluation of seismic response of LCUP were provided in this paper.