Properly designed expansion joint to ensure successful seismically Isolated Structures

Seismic isolation system has become one of the most efficient approaches chosen by design engineers for having better seismic performance and cost-efficiency for structures located in high seismicity area. For bridges, the seismic isolation system is usually done by replacing the conventional bearings (pot or spherical bearings) with seismic isolator bearings (rubber isolator bearings or pendulum bearings). In general, only these isolator bearings that will be the focus of considerations during design phase. It is commonly forgotten that the seismic isolation system shall be also coupled with properly installed seismic expansion joint that can accommodate large movements on the bridge deck due to isolation effect of the seismic system. Improperly designed expansion joint is usually shown by the use of small non-seismic joint that leads to very narrow provided gaps in between the concrete deck and its adjacent structure. These gaps are not able to accommodate large movements on the deck of a seismically isolated bridge. Collisions or poundings during seismic event are inevitable. This leads to dysfunctionality of seismic isolation system, and in the worst case it may generate excessive impact forces that will result to undesired performance level and damages on the structures.