Investigation of the Live-Load Effects on Long-Span Bridges under Traffic Flows

Different from short-span girder bridges, long-span bridges support a large amount of traffic, which significantly influences the dynamic performance of the bridge. The design live load on long-span bridges has seldom been investigated to take into account the dynamic effects from multiple vehicles in traffic flow. The current AASHTO LRFD specification was primarily developed for and calibrated from bridges with spans of 61.0 m (200 ft) or less. Therefore, it is unknown whether it is risky or conservative to use the same design live load from AASHTO on long-span bridges with spans longer than 100 m. Taking advantage of the advanced simulation methodology on the coupled bridge-traffic system developed recently, the live-load effects on a prototype long-span bridge from stochastic traffic flow were comprehensively studied, including the extreme dynamic response and the dynamic amplification factors for different bridge components. To evaluate the applicability of the design live-load in the current AASHTO specification on long-span bridges, the load effects on the prototype long-span bridge were numerically assessed and were compared with the corresponding response envelopes of the bridge under stochastic traffic flow. It was found that the design live load from AASHTO may be unsafe for use as the live load for the design of the bridge girder, pylon, and stay cables for long-span bridges.