A rigid-frame suspension composite bridge for mid-span deflection control: Static, long-term, and seismic performance

Excessive mid-span deflection is a critical serviceability issue in long-span continuous rigid-frame bridges, while conventional design schemes have limited ability to improve deformation control without compromising overall structural performance. To address this issue, a rigid-frame suspension composite bridge is proposed, and its mechanical and seismic behavior is investigated. Refined finite element models are established in MIDAS Civil and OpenSees and validated against field modal test results. Comparative analyses are then conducted against a conventional continuous rigid-frame bridge with the same span arrangement in terms of static response, long-term shrinkage and creep effects, dynamic characteristics, nonlinear time-history response, and seismic fragility. The results show that the suspension system significantly redistributes internal forces, reducing the negative bending moment at the pier tops by about 50%, the completion-stage mid-span deflection by about 80%, and the long-term deflection after ten years by about 28%. Active cable re-tensioning during service can further reduce mid-span deflection while maintaining acceptable structural responses. Seismic analyses indicate consistently lower pier vulnerability across all damage states, whereas bearing fragility becomes higher at the complete damage state. Overall, the proposed system improves serviceability and modifies the distribution of seismic fragility among components.