Tides, Weather Create Design Challenges For New Bay Bridge
SAN FRANCISCO (CBS) – It’s a flow of water bigger than the mighty Mississippi River – 390 billion gallons of water move in and out of San Francisco Bay twice a day, creating an engineering challenge for the designers of the new Bay Bridge.
The water depth, where the bay meets the ocean, is more than 300 feet. The average water depth in the bay is only 14 feet. All of that energy gets shoved up near the surface, creating strong currents and very large tides.
Boaters know how hazardous the currents can be, but imagine building a multi-billion-dollar structure right in the middle of that tide.
Builders of the Bay Bridge’s cousin, the Golden Gate Bridge, had it much worse working on the footings there. They struggled with the epic tidal flow right at the mouth of the bay. It was still no easy task getting this newest project off the ground.
It’s Dave Perkins’ job to keep the workers safe as they install The Bay Lights Project.
“For us up on the bridge there is no second guessing,” Perkins said.
The project is comprised of 25,000 L.E.D. lights on the older part of the Bay Bridge. That’s not an easy task, especially when it comes to the extreme weather often found at the top of the Bay Bridge. Perkins compares it to a wind tunnel.
In fact, a wind gust of 30 miles an hour in San Francisco can easily translate to a 50, 60, or 70 mile an hour gust at the top of the bridge, due to less friction and more height.
Brian Maroney is one of the top engineers working on the bridge. There are many micro-climates throughout the Bay Area, but Maroney said there are many micro-climates just on the bridge. That’s why engineers set up their own weather stations to compile the best wind data possible.
“We collected site specific wind studies. It (the bridge) is only 5 meters deep, 385 meters long, and very wide. It almost looks like an airplane wing, and it can act that way,” Maroney said.
Nobody wants it to act that way. Maroney said it would be akin to the Tacoma Narrows Bridge south of Seattle back in 1940, when strong winds and a poor design led to something called flutter.
Maroney said that’s led to big-time engineering changes ever since.
“We actually designed for a 10,000 year return period for flutter,” Maroney said.
Maroney said the design of the new Bay Bridge includes wind vortex shutters installed under the road-bed to minimize the impact of strong winds. Maroney said it’s just one of the many ways the bridge is designed to defeat whatever mother nature throws its way.