In 1954, the U.S. Coast Guard built a suspension footbridge to access the Point Bonita Lighthouse on the outer northwestern point overlooking the Pacific Ocean and San Francisco Bay. Over the years, the bridge had been renovated, but needed to be replaced in 2012. Before a new bridge could be constructed, the rock face needed to be stabilized. The point’s rock mass was fracturing and displaying signs of instability due to years of exposure to harsh marine elements. Stabilization was required to support the weight of a modern bridge without fracturing further.
A stainless steel SPIDER® S4-230 was installed to stabilize the rock face. The solution itself is a stainless steel rolled cable net system that has a breaking strength of greater than 12,000 pounds/ft. The diamond shaped net is comprised of three looped and twisted 3 mm strands of steel with a tensile strength of 212 ksi and a diameter of 0.339 inches. As required by National Park Service, the net was powder coated bronze to better blend with the natural color of the rock mass and further protect against corrosion.
The project won ENR California’s Best Small Project-Construction award in 2012.
Photo courtesy of Stephen Gainsboro