Optimized Design And Mechanical Properties Of Two Precast Concrete Box Culverts

At present,there are still many problems in the research of precast concrete box culverts at home and abroad,such as the complicated calculation of spring hinge model of two-part box culverts and the need for joint test,and the insufficient research on settlement of twin box culverts.In this paper,the new theoretical calculation models were proposed for the single-compartment two-part culverts firstly,which were also applied to the multi-compartment box culverts.Secondly,the uneven settlement of the foundation of the twin box culverts was studied.The main research contents include the following aspects:（1）Seven simplified plane frame models were proposed for the joint design of the two-part box culvert,and the axial compression cantilever model was selected for theoretical calculation,experimental analysis and numerical simulation.The results show that the yield load and failure load of the culvert were respectively 3.06 times and 3.54 times of the designed bearing capacity,the ductility coefficient of joint deflection reached 2.85,and the safety margin was very high,thus validating the reliability of the theoretical model.In addition,the influence of different factor combinations on the structural performance was studied by numerical simulation.Combined with the evaluation index and other aspects of analysis,it was found that the sliding chain rod model had the highest fitting degree and comprehensive performance for the actual box culvert,so it is recommended to be used for the reinforcement calculation.What’s more,it is suggested that the diameter of the prestressed tendons and the tension control stress should be 6mm and 0.35 f_pu respectively,and unbonded prestress should be used for construction.（2）The sliding chain model and relevant suggestions of the single-compartment two-part culvert were applied to the multi-compartment two-part culvert,thus verifying the universality of the theoretical model and suggestions.In addition,the influence of partition on the performance of the box culvert was discussed,and it was found that although the partition wall only beared a small bending moment（mainly bearing axial force and shear force）,it could make the force of the whole structure more uniform,and significantly improved the overall performance of the box culvert.Therefore,for large size box culverts,the multi-compartment form should be chosen.（3）For longitudinal deformation of twin culverts caused by uneven settlement of foundation,it was found that the main factors limiting the vertical resistance ofthe box culvert to the deformation of the foundation were the ultimate clearance quantity at the joint of the box culvert and the longitudinal length of the box culvert,based on the calculation formula of the longitudinal ultimate settlement value.In the transverse aspect,the minimum transverse reserved space of the flexible unconnected box culverts was derived,and the check calculation of the connection part of the rigid connected box culverts was given.Through comparison,it was found that the comprehensive benefit of flexible twin culverts is higher.In addition,the comparison between twin culverts and integral multi-compartment culverts was made from the perspective of economy,and it was found that twin culverts was better than integral multi-compartment culverts.Therefore,in the case of no size limit,the flexible unconnected twin culverts should be preferred.