Epoxy-Tie® Adhesive Selected for use in the country's largest Seismic Retrofit Project!
Chosen for the ease of use and performance during testing in adverse conditions, Simpson's SET epoxy was selected for upgrading the connections of The San Francisco - Oakland Bay Bridge to its 120 foot deep caisson foundation.
The Bay Bridge retrofit is part of the California Department of Transportation's (CALTRANS) $2.6 billion toll bridge seismic upgrade. The cable suspended west span was constructed in 1931 to match the appearance of the Golden Gate Bridge. The retrofit strengthens the support structures; the massive cable anchorage located mid-span, and the connections of the towers to the caisson footings. "The purpose of the retrofit is to bring the bridge's service level up to a higher anticipated earthquake demand," said CALTRANS senior project engineer Mark Reno.
Due to the logistics of getting material from shore to the piers at the bases of the bridge supports, convenience and portability were major considerations. "We were mostly looking at ease of placement and constructability." Said Reno when questioned about the key issues surrounding the design considerations and product selection. "We have a large amount of reinforcing in the holes, around which we're trying to fill the voids and get complete bonding." Much of the work took place inside the caissons on scaffolding supported from overhead beams placed across the top of caissons. Gaining access inside the caissons required hand jack-hammering through multiple walls of concrete up to 2' thick. Working and staging room was at a premium. Tools, equipment and materials had to fit through openings often no more than 3' square.
The Towers were strengthened in a three-step process. Eight foot tall holdowns were attached to the steel towers, with 3" diameter rods extending down through the existing caisson caps. The mass of the concrete caisson caps was increased to extend farther down inside the caisson. Collector plates were then added approximately twelve feet below the caps and evenly spaced around the inside of the caisson. Each collector was anchored with eight, 1" diameter rods installed in epoxy. The cap was then connected to the collectors using high strength steel rods. In the event of a large earthquake, this design will transfer the bending moment over a much larger area of the footing than would have been possible in a conventional design without adding a significant amount of concrete.
Job superintendent, Roger Brown of West Coast Bridge out of Benecia, CA said his company selected Simpson's Epoxy-Tie® because it was cost effective, his crews liked working with it, and it passed their own tension testing on site. "I tried other brands and the crews had problems with them. So you tend to go with something that's worker friendly and reliable." Brown said Simpson provides a complete system "It's the way the system is put together," he explained. The tools are designed to handle the viscosity of the epoxy and mixing nozzles are available in different diameters to match the dispensing rate to the hole size. "When you pressurize this (epoxy) with a pneumatic dispensing tool that takes it and pushes it in..sometimes with other products we've had leakage out of the back side of the tubes causing a big mess. After you use hundreds of tubes with dust all over the place.we don't like that. They (the installers) don't want to get the stuff all over. The system works. We didn't have any big hassles - no waste, " Brown added.
Simpson Strong-Tie is headquartered in Pleasanton, CA. For more information on Simpson products call 800/999-5099.