East Fork Road over North Fork San Gabriel River Bridge Retrofit (Finalist)

The East Fork Road Bridge over North Fork San Gabriel River is a 642-feet long, steel truss bridge built in 1949. It is located in the San Gabriel Mountains National Monument just north of the City of Azusa and provides access to L.A. County firefighting facilities and recreational amenities such as the East Fork Trail that leads to the “Bridge to Nowhere”. The project consisted of seismically retrofitting the bridge to prevent collapse after an earthquake and is outstanding and worthy of an award due to its high level of structural engineering complexity, use of innovative technology, safety benefits to the public, and sensitivity to the environment. It also demonstrates how collaborative efforts and open dialogue among owner, engineer, and contractors can resolve project challenges and bring the project to a successful conclusion. Respecting the environment and ensuring that the project did not negatively impact the surrounding area and wildlife was a high priority. Several alternatives were considered when developing the retrofit strategy. Ultimately, an innovative approach was selected that minimized impacts on the environment. Due to the high seismicity at the site, traditional retrofit methods required significant and costly modifications to prevent collapse. So instead of strengthening bridge members and the foundation, a retrofit strategy was developed to reduce the seismic forces by altering the bridge’s structural response. This was achieved by replacing the existing bridge bearings with seismic isolation bearings that allowed the bridge to behave more flexibly during an earthquake. As a result, the number of members that required strengthening was greatly reduced and the need for foundation retrofit was eliminated. A construction method was also developed that did not involve accessing the river. This required an extensive scaffolding system be constructed from atop the bridge and hung from the bridge members. Large and heavy steel bracings and the bridge bearings had to be removed and reinstalled from this scaffolding. Additionally, construction was halted twice for an extended period of time to ensure that birds nesting on the bridge were not impacted. The innovative use of seismic isolation bearings combined with selective member strengthening proved to be a cost effective and environmentally friendly solution that did not require any construction work in the riverbed. With great collaborative efforts, open dialogue, and close coordination amongst L.A. County staff, JMEC Engineering Inc., John S. Meek Company Inc., and Seismic Energy Products, the project was successfully completed in May 2016. The risk of a bridge collapse from a strong earthquake has been greatly reduced, public safety has been improved, and access for critical firefighting facilities and recreational amenities have been preserved by this bridge seismic retrofit project that was constructed in an environmentally responsible and sustainable manner.