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

• The premature failure of finger-type bridge expansion joint is explained by the asymmetric vibration of the joint plate.
• A new failure mode based on the asymmetric vibration is proposed for the design of finger-type bridge joints.
• A simple design formula is developed for the new failure mode by using an energy principle.
• The effect of this asymmetric vibration is verified by a set of lab-scale experiments and three dimensional FE simulations.
• A simple modification of finger-joints is proposed to reduce the large reaction of the anchor bolts efficiently.

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.