Field Investigation of Causes of Fatigue Damage in Web Gap Plate Based on Strain and Displacement Measurements in In-Service Steel Girder Bridge

As the number of steel bridges that have been in service for more than 40 years in Japan increases, several types of fatigue damage have been recognized. In particular, damage to web gap plates is often found in metropolitan expressway. In order to implement appropriate repair and reinforcement procedures for damage caused by displacement-induced fatigue, it is important to determine the deformation that results from the passage of vehicles that leads to high strain. Therefore, in the present study, the causes of fatigue damage in web gap plates in an in-service steel girder bridge were investigated using contact displacement gauges, tri-axial strain gauges and microelectromechanical systems inertial measurement units. From the displacement and strain measurements, it was found that most of the strain that occurs in the web gap plate are due to slab deflection. Furthermore, the sign (positive or negative) of the strain response was shown to depend on the driving lane.