Without interrupting the traffic on the old bridge, the connection of the widening bridge will cause disturbance to the concrete in the splicing position. In order to study the anti-disturbance performance of concrete material, the Normal Concrete (NC) material and the Ultra-High-Performance Concrete (UHPC) material were experimentally investigated by the vertical shaking table and X-ray computed tomography scanning. It can be learnt from tests that the compressive strength of NC and UHPC can be increased by about 10% to 20% after disturbance, while the flexural tensile strength and splitting tensile strength of both NC and UHPC can be reduced by about 20% to 25% and 10% to 20%, respectively. The elastic modulus of UHPC is not significantly affected by the vibration disturbance, and that of NC can be increased by about 20%. The setting time difference of the proposed NC material can be controlled within 100 min, and it can improve its anti-disturbance performance. Excessive vibration disturbance affects the internal structure of NC, while it has little effect on the distribution of steel fiber in UHPC. Due to the high cost of UHPC materials, it is recommended to analyze the joint performance requirements before the selection of splicing materials. If the stress requirement is not particularly high, it is still recommended to apply the proposed NC material for the splicing of widening bridge.

For the purpose of splicing widening bridges without interrupting traffic in expressway reconstruction and extension projects, different types of anti-differential disturbance concrete (ADC) were developed. This paper experimentally investigated the mechanical performance of ADC under the influence of traffic–vehicle coupling vibration. The experimental device, with one end fixed and the other end vertically vibrated, was designed to simulate vehicle–bridge coupling vibration on an existing old bridge. Different disturbance degrees were simulated by adopting specimens made with standard molds and integral plate molds. The compressive strength and other performances of normal-type ADC (NADC) and high-performance ADC (HPADC) were tested. Owing to the differential disturbance, the compressive strength of the NADC increased by 10~20%, and that of the HPADC was almost unaffected. The flexural tensile strengths of the NADC and the HPADC were decreased to some extent. NADC and HPADC can both meet the requirement of widening bridge splicing, and the anti-differential disturbance performance of HPADC is superior to that of NADC.

Compared to conventional reinforced concrete (RC) piers, self-centering rocking piers exhibit better seismic resilience and sustain minor damage. However, their construction typically relies on prefabrication. Moving large, prefabricated components can be challenging in mountainous areas with limited transportation access. Therefore, using concrete-filled steel tube (CFST) piers is a practical alternative. The steel tube both serves as a construction permanent formwork and enhances the compressive performance of concrete through confinement effects. To apply CFST self-centering rocking piers in mountainous regions with high seismic intensity, a fast construction system was designed and a 1:4 scale specimen was developed for testing. Lateral cyclic loading tests revealed that the specimen exhibited good deformation and self-centering capabilities, with a residual drift ratio of only 0.17% at a drift ratio of 7.7%. Most of the horizontal displacement was contributed through a rocking gap opening, resulting in minimal damage to the pier itself. The damage was concentrated primarily in the energy-dissipating rebars, while the prestress strands remained elastic, though prestress loss was observed.

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.

For an existing bridge constructed with separate spans, the ends of adjacent flanges are disconnected. The problem of separated driving may occur at the bridgehead position after traffic conversion. The idea of integral splicing two separate spans of the existing long-span bridge is proposed. Direct crossing of a vehicle between the two separate spans of the existing long-span bridge can be realized. Firstly, the demand for integral splicing of the existing box girder bridge is analyzed using different methods. Then, an integral splicing composite structure (ISC-Structure) is designed and tested, and the corresponding design method is summarized. Finally, the construction technology for the ISC-Structure is optimized based on the actual field conditions. This research shows that the integral splicing demand of the old bridge can be obtained through on-site monitoring at the splicing position. Furthermore, the proposed random traffic flow simulation method can be applied to expand the data volume and verify the validity of the monitoring data. The proposed ISC-Structure meets the transverse splicing requirements of the Xinfengjiang Bridge. It can effectively connect the two separate spans, enabling them to work compositely and improving longitudinal mechanical properties. A layered and segmented construction scheme is proposed, and the relevant construction technology is optimized for the target integral splicing project. The proposed integral splicing design and construction technology can sever as a reference for similar long-span bridge extension projects.