Study On The Effects Of Bridge Pier Settlement On Joint Forces And Constant Force Self-Adaptive Devices

The phenomenon of edge biting or cracking at the joint of old and new bridge connections is a pressing issue in bridge widening projects.This article focuses on the Lishui North River Bridge reconstruction and expansion project on the G60 ShanghaiKunming Expressway from Liyuan to Dongxiang,and systematically studies the mechanical issues that arise at the joint of the upper structure of box girder bridges due to the settlement of bridge piers during widening,resulting in cracking and damage.The study investigates the relationship between pier settlement and the stress and deformation of the upper structure and its joints under the condition of uniform settlement of the new bridge piers using theoretical analysis,numerical calculations,and miniature experiments.The article presents several suggestions to reduce joint stress and designs a constant force adaptive device installed at the bearings to reduce the normal stress at the joint.The main research content and results of this article are as follows:The bridge widening schemes,joint widening methods,and upper connection methods in bridge widening projects are summarized,and the advantages,disadvantages,and applicable types of different connection methods are discussed.The study selects the lateral widening method recommended by the specification,which connects the upper structure and does not connect the lower structure for research.The various settlement modes are described,and the allowable settlement values are selected.The uniform settlement of 1mm,2mm,3mm,4mm,and 5mm of the new bridge piers is selected as the research condition.Based on the matrix displacement method,the theoretical analysis of the widened upper structure of the bridge is conducted,and the corresponding semi-rigid connection mechanical model of the upper structure is established.For the given settlement of the new bridge piers,the maximum normal stress expression at the joint is derived.It is found that the maximum tensile and compressive stress of the joint is proportional to the elastic modulus of concrete,the total thickness of the top plate and bridge deck,and the settlement amount,and inversely proportional to the square of the length of the top plate and wing plate.Finite element calculations are conducted,and the results are compared with the theoretical values.The results of the finite element calculations and the theoretical expressions are basically consistent.The upper structures with flexible connections,semi-rigid connections,and rigid connections are calculated using finite element software to analyze the stress states of the three connection forms.According to the calculation results,it is found that the stress state of flexible connection and semi-rigid connection is similar,and the maximum normal stress at the joint of the flexible connection is greater than that of the semi-rigid connection.The stress state of the rigid connection and semi-rigid connection is different,and the maximum normal stress at the joint of the rigid connection is less than that of the semi-rigid connection.Based on the theoretical expression of the maximum normal stress at the joint,several structural suggestions are proposed to reduce the maximum normal stress at the joint.A constant force adaptive device installed at the inner support of the new bridge is designed,which can reduce the settlement of the inner support point of the upper structure during the settlement of the new bridge,thereby reducing the maximum tensile and compressive stress at the joint.The maximum reduction in tensile and compressive stress is 68.7% and 66.3%,respectively,as calculated by the finite element software.by conducting further micro-scale experiments to verify the correctness of the theoretical expressions,a comparison was made between the theoretical and experimental values,which differed by 27.07%.Taking into account the possible errors between the experiment and the design,it is deemed acceptable.