Seismic Upgrading
Structures have to withstand large horizontal and vertical accelerations and dynamic forces during earthquakes. This creates special requirements on the stiffness and load-bearing capacity of the structural members as well as on their connections.
Many existing structures must be improved to survive future earthquakes. In California, following the Loma Prieta (1989) and Northridge (1994) earthquakes, approximately 1,300 concrete and steel structures needed seismic upgrading.
Retrofitting of Bridges
An essential seismic upgrading measure of bridges is to avoid the loss of support for the bearings due to large relative displacements between the superstructure and the substructure. These measures should not impede the free movement of the structure due to temperature variation or other effects.
Often, the existing pier cap beams must be widened and strengthened and the superstructure must be restrained to the support. Each of the following retro fittings made use of post-tensioning tendons to increase the stability of the structure.