Analysis of Key Technologies and Mechanical Characteristics for the Demolition of Adjacent Twin Continuous Girder Bridges

With the update of urban infrastructure, the demolition of damaged bridges is increasing, and the routine demolition of old and dangerous bridges in urban areas is prone to brittle fracture and secondary disasters. Exploring the key technologies and stress characteristics for the demolition of the Wuyakou Bridge, which is located in a complex working condition with double adjacent spans, asymmetric spans, and only 9.5 meters away from the subway. Based on the analysis of the diagonal cracks in the web plate of the old bridge and the deflection of nearly 180 mm in the mid span, a "static" demolition plan combining static cutting and gantry crane is proposed. A finite element model was established using Midas Civil, and the stiffness degradation effect of the old bridge was simulated by reducing the elastic modulus of the material (0.9E). The entire demolition process was simulated and monitored. The research results indicate that the reverse demolition process of "closing the dragon section first, rear span, and then cantilever symmetry" can limit the unbalanced bending moment of the bridge pier to within 60% of the anti overturning limit; During the demolition process, through reasonable process arrangement, the maximum compressive stress of the key section of the main beam was −14.7 MPa, and the measured deformation deviation was within ±5 mm, all within a safe and controllable range. This solution has successfully solved the problem of micro vibration control and double bridge interlocking construction in the vicinity of the subway protection zone, and can provide theoretical basis and technical reference for the demolition of urban bridges in similar complex environments.