Do expansion joints between parking-deck slabs allow for differential vertical slab movement when one slab carries much greater loads -- due to more vehicles -- than the other slab?
Joint detailing determines whether or not a parking-deck expansion joint deflects. In cast-in-place construction, the joint often occurs over a beam, permitting horizontal but not vertical movement. Differential vertical movement is undesirable for some joint-sealing systems -- such as those with cover plates -- because the deflection would interfere with the seal. Also, if the deck will be snowplowed, the plow blade would hit the raised portion of the deck if the other side were allowed to deflect. In precast/prestressed parking decks built with double tees, there may be a shear key to prevent deflection of one double tee relative to the adjacent one. Or beams may be close enough to the joint to prohibit excessive movement. Some joint-sealing systems permit both vertical and horizontal movements, and if there is no other reason (such as snowplowing) for not permitting vertical movement, some vertical movement may be acceptable.