The simplified model and numerical investigation of U-section precast concrete box culverts

U-section precast concrete box culverts (UPCBCs) are recently widely used in utility tunnels, and the design of UPCBCs necessitates the consideration of transverse and longitudinal aspects. To avoid the challenge of determining the joint stiffness and to consider the soil-culvert interaction, seven simplified transverse frame models based on the elastic foundation beam method were proposed. Through 162 three-dimensional numerical models, the structural responses under representative parameters (e.g. the burial depth, construction methods, and soil properties) were investigated to seek the optimal joint simplification. The data from parametric analysis were utilized to establish the evaluation indexes for the synthetical value of models, and it was found that the sliding link model (SLM) was the optimal model, followed by the overall model (OM). Additionally, the upper bound theorem was employed to conduct a theoretical investigation into the ultimate load. When accounting for the haunches of the culvert, the results of SLM and OM are similar to those derived from FEM. Moreover, considering the shear effects of the structure and the foundation, a modified longitudinal continuous equivalent model based on the theory of Timoshenko beams and Vlasov foundations was proposed. The boundary value problem for the longitudinal model within a settlement interval was numerically solved, and the impacts of shear effects on structural responses were compared when the external action was a uniformly distributed load or a field measured longitudinal deformation of a Shanghai metro tunnel. The results will further contribute to the study, design, and application of UPCBCs.