A simplified design-oriented pedestrian load model considering pedestrian-bridge interaction for footbridges

Pedestrian-bridge interaction (PBI) significantly influences the dynamic behavior of lightweight, flexible, and low-damping footbridges. Current design codes commonly adopt the Force Model (FM) for pedestrian loading, which neglects PBI and leads to overestimated structural responses. Although the Spring -Mass-Damper Model (SMDM) captures PBI, its computational complexity limits practical use. Thus, it requires a simplified yet computationally practical approach that not only accounts for PBI but also is applicable to both higher-mode and higher-harmonic resonance scenarios. To address this gap, dynamic tests were performed on a simply supported footbridge with low natural frequency and damping. Extensive simulation was done based on the bridge to compare the responses under single-harmonic (HF1) and three-harmonic (HF3) load models, being implemented via both FM and SMDM. A subsequent parametric study under Random Crowd Loading (RCL) investigated various resonance conditions. The results highlight the necessity of incorporating higher-order harmonics in load models for footbridges susceptible to harmonic resonance. Although Equivalent Crowd Loading (ECL) methods from guidelines perform well for resonance scenarios, they overestimate acceleration responses relative to SMDM benchmarks. Therefore, reduction factors were introduced within the SMDM framework to calibrate the equivalent pedestrian number. The resulting ECL-SMD model yields acceleration estimations agreeing with the response from RCL-SMD analysis. The method was further verified through case studies on two suspension footbridges, demonstrating its applicability to complex structural systems.