Optimum design of seismic joints in bridges

Andreas Kappos
Khalifa University, Abu Dhabi, UAE

A key aspect of seismic design of bridges is the appropriate selection of joint gaps, an issue that has not received enough attention so far, while pertinent code provisions are far from comprehensive. End gaps define the boundary conditions of the bridge and affect their dynamic response; their proper design can lead to an improved structural performance under dynamic actions.

The first part of this lecture will assess the effect of joint gap size on the seismic response of bridges and put forward a methodology for optimising this size, using a number of criteria such as maintaining the functionality of the bridge for moderate earthquakes, ensuring the safety of the bridge under earthquakes stronger than that used for code design, and, last but not least, optimising the cost of the bridge (as a function of gap size) using a life-cycle cost approach.

The second part will revisit the concept of the ‘Dynamic Intelligent Bridge’ recently introduced by the author, wherein the idea is to substitute current bridge joints that have a fixed width with variable-width joints, wherein under seismic loading the joint gap is optimised either with a one-off adjustment, or continuously varying through semi-active control. In all cases a novel device is used that permits this improved behaviour of the joints, the moveable shear key (MSK), a device for blocking the movement of the bridge deck, which has the possibility to slide, hence varying the size of the existing gap between the deck and the abutment.