DYWIDAG Strand Tendons Stabilize World’s Longest Stress-Ribbon Bridge in California

The 300m (990ft) long David Kreitzer Lake Hodges Bicycle/Pedestrian Bridge in San Diego, California is the world’s longest stress-ribbon bridge. The bridge runs through San Dieguito River Park and offers cyclists a safe alternative to the main highway. As it crosses an environmentally protected lake and its impact on the environment had to be minimized, the pedestrian and bicycle bridge was built as a stress-ribbon bridge.

The bridge is a suspension type structure divided into three 100m (330ft) long spans, the post-tensioning tendons of which are integrated into an extremely thin, only 410mm (16in) strong bridge deck. Thanks to the post-tensioning systems used, the bridge is supported by two piers and blends into the surrounding environment.

Complex methods of analysis were needed to represent the nonlinear behavior of the post-tensioning system and the structure’s time-dependent changes. In addition, construction was restricted to the winter months in order not to interfere with the nesting periods of several local bird species. A total of 87 precast concrete elements were needed for the construction of the bridge deck.

Post-tensioning work was performed by DSI USA from a temporary trestle that extended approximately 213m (700ft) from one end of the structure. Initially, approx. 39,000m (128,000ft) Type 19x0.6" DYWIDAG Strand Tendons with MA Anchorages were installed. The primary tendons required for this purpose were prefabricated on site and installed across the open spans using temporary post-tensioning tendons.

Once stressed to a predetermined sag, the precast deck panels were hung into their final position and additional Type 27x0.6" Post-Tensioning Tendons with MA Anchorages were installed in troughs formed in the precast sections.

Following installation, the primary strand tendons were adjusted to the final sag required by the engineer, and final concrete was placed in all troughs and closures. As the concrete cured, the Type 27x0.6" Secondary Tendons were stressed incrementally to control shrinkage. Secondary tendon ducts were fully grouted following completion of stressing.

As one of only six stress-ribbon bridges in North America and one of less than 50 stress-ribbon bridges worldwide, the David Kreitzer Lake Hodges Bicycle Pedestrian Bridge was chosen as a co-winner in the “Non-Highway Bridge“ category in PCI’s Design Awards Program.