Lateral Stability of Vehicles Crossing a Bridge during an Earthquake

Abstract

During the 211 Great East Japan earthquake, the rollover of a truck crossing the Yokohama Bay cable-stayed bridge was reported. A similar incident was also reported at the viaduct of the Hanshin-Expressway during the 1995 Hanshin (or Kobe) earthquake. Rollover of a vehicle can cause damage to the bridge, injury to the driver, and damage to other vehicles. Moreover, the incident can create hours of blockage of the major traffic line and impede postdisaster relief efforts. Currently, there are very limited studies on the effect of the seismic response on the stability of moving vehicles. This paper presents a general analytical framework for the analysis of the lateral stability of a vehicle crossing a bridge during an earthquake. An equation of motion for a two-axle vehicle under seismic excitation from a bridge girder was developed considering in-plane and out-of-plane vehicle motions and a driver reaction model. Numerical simulations were conducted using three-dimensional finite elements of the Yokohama Bay cable-stayed bridge using ground accelerations recorded during the 211 Great East Japan earthquake as the inputs. Results of the simulation showed that the significant bridge-deck vibration due to an earthquake reduces the effective normal force on vehicle wheels. To evaluate vehicle stability, two conditions were studied: rollover and lateral-slip stability. Rollover stability defines the critical condition that might lead to a rollover and that is related to zero normal force on the wheels. The lateral-slip stability relates to the lateral force equilibrium between the earthquake-induced lateral force and the slip resistance provided by wheel friction. Case studies and discussions involving different driving responses, such as deceleration, and the driver’s reaction model were provided for both stability conditions.