Local Full-Scale Model Test on Mechanical Performance of the Integral Splicing Composite Structure of Adjacent Existing Box Girder Bridges

Adjacent existing box girder bridges should be spliced in the long-span bridge expansion project. A type of integral splicing composite structure for connecting the adjacent flange plates is designed herein. The mechanical characteristic of the integral splicing composite structure is tested using a local full-scale model, and a refined simulation model is also proposed for the optimization of the integral splicing composite structure. The loop bar in the joint connection segment and the application of Ultra-High-Performance Concrete (UHPC) material can guarantee the effective connection between the existing flange plate and the splicing structure. The embedded angled bar can delay the interface debonding failure and interface slip. The UHPC composite segment below the flange plate (segment CF) can bend together with the existing flange plate. In this study, an innovative integral splicing composite structure for a long-span bridge extension project is proposed and verified using both a local full-scale model test and finite element simulation. The adaptation of UHPC material and loop bar joint connection form can meet the cracking loading requirements of the splicing box girder structure. By proposing a refined simulation model and comparing the calculation result with the test result, it is found that the flexural performance of the integral splicing composite structure depends on the size of the composite segment below the flange plate (segment CF). Increasing the width of segment CF is beneficial to delay the interface debonding failure, and increasing its thickness can effectively delay the cracking load of the flange plate. Finally, the scheme of segment CF with one side width of 200 cm and a minimum thickness of 15 cm can improve the flexural resistance of the spliced structure and avoid the shear effect caused by the lane layout scheme and the location of the segment CF end. Through the research in this paper, the reasonable splicing form of a long-span old bridge is innovated and verified, which can be used as a reference for other long-span bridge splicing projects.