A simplified structural mechanics model for cable-truss footbridges and its implications for preliminary design

Compared with traditional suspension footbridges, the cable-truss footbridge is always easier to satisfy structure deformation requirements under small dead-load-to-live-load ratio condition, and it enjoys surging popularity in western China. In this type of bridges, the deck system is designed as a pure local load-bearing member, and the inverse pre-tensioned deck cable system is set up to form a tension–tension mechanical system. To better understand its structural performance, a simplified structural mechanics model for cable-truss footbridges is proposed, and the analytical formulations for deformation and internal forces of the bridge under entire span live load as well as semi-span live load have been derived. The reliability and accuracy of the proposed model have been validated in a comparison study with the finite element analysis. Furthermore, a series of qualitative and quantitative parametric studies have been conducted, which reveal that the cable-truss bridges have several novel structural characteristics that differ from that of traditional suspension bridges. Finally, the affordability range of cable-truss bridges is also discussed by using material usage analysis.