Kinematic modeling and dual-strategy heuristic screening of ductile hinge layout for multi-body coordinated incremental launching of spatial curve bridges

Multi-body coordinated incremental launching (MCIL) provides a construction route for spatially curved bridges under constrained sites, but full-stage geometric posture and ductile-hinge layout still require efficient pre-construction evaluation. This study develops a geometric-kinematic framework based on composite rigid bodies (CRBs) and couples it with a dual-strategy heuristic for ductile-hinge layout. The CRB system is updated through chainage-based boundary lookup, and spatial posture is obtained with a safeguarded endpoint-based Rodrigues transformation. The heuristic combines a proximity rule for lateral-deviation exceedance with global candidate assessment for height-difference exceedance; it seeks a feasible low-cardinality layout. For a 1991 m, 36,000 tonne steel box-girder viaduct, one 772 state simulation required approximately 14 s. Five hinge additions reduced the maximum lateral deviation from 2.997 to 0.911 m and the maximum height difference from 1.727 to 0.586 m. Internal geometric and convergence checks support numerical consistency. In 100 fixed-layout simulations with independent 10 mm coordinate perturbations, the fixed layout remained within the 1.0 m and 0.8 m constraints. This study links kinematic simulation to hinge-layout screening, providing a quantitative design tool for MCIL of spatially variable curve bridges.