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.
       DSI Reference: Elisian Viaduct, Los Angeles, CA, USA
       DSI Reference: Los Angeles County, Intersection Freeway, CA, USA
       DSI Reference: Altamount Sidehill Viaduct, Northern California, USA
       DSI Reference: Cahuenga Boulevard Underpass, Los Angeles County, CA, USA

Retrofitting of Buildings
Deficient structural systems or elements require strengthening to withstand future earthquakes. DYWIDAG Bar Tendons, with their easy and reliable anchorage and coupling systems, can be applied to upgrade these structures.
       DSI Reference: Oakland City Hall, Oakland, CA, USA
       DSI Reference: Glendale Post Office, Glendale, CA, USA
       DSI Reference: California State University, Long Beach Parking Structure, CA, USA

Retrofitting of Foundations
In order to withstand the increased loading on structures during a major seismic event, DYWIDAG Ground Anchors as well as GEWI ^® Piles are used to enhance bearing capacity and reduce foundation deformations.
       DSI Reference: Steel Water Tanks, Contra Costa County, CA, USA
       DSI Reference: Telecommunication Tower, Diepenbeck, Belgium
       DSI Reference: Britannia Secondary School, Vancouver, British Columbia, Canada
       DSI Reference: Los Angeles River Bridge, Long Beach, CA, USA