Asymmetric vibration of finger-type bridge expansion joint for design consideration

An asymmetric vibration is proposed for the design consideration of finger-type bridge joints. It is shown, both experimentally and numerically, that the vibration of the joint-plate is not symmetric, but asymmetric; and that the end moment of finger-type bridge joints becomes maximum when the joint plate springs upward, after the load moves out from the joint, in which the tension of the anchor bolts due to this upturned vibration is much greater than the static load case with the load at the tip of the joint-plate. A simplified design formula is developed based on an energy concept, to consider this new failure mode in the design procedure. It is shown that the actual maximum moment and tension can be closely estimated by a simple formula.