Bay Bridge span designed to endure major quake

Twenty years after the Loma Prieta earthquake shook loose a 250-ton section of the Bay Bridge, state transportation officials vowed Monday that the long-planned replacement span will be built to better withstand a major temblor.

"When the bridge is complete, it's going to be one of the most seismically advanced structures in the world," Caltrans spokesman Bart Ney said.

On Monday, Caltrans released a computer-generated simulation of how the new East Bay segment of the bridge - set to be completed in 2013 - is expected to respond when jolted by a large quake. The simulation can be viewed at tr.im/BAa2.

In the depiction, the bridge sways and undulates, moving with the earth's rumbling rather than resisting it. Imagine an undersea kelp forest pushed and pulled by a strong tide.

The beams connecting different sections of the bridge are designed to absorb the earthquake's energy and protect the main structure. The damaged beams then can be swapped out

The soaring 525-foot-tall tower of the planned self-anchored suspension span on the East Bay portion of the Bay Bridge will be held up by four steel legs, each able to move independently. The legs will be connected by replaceable shock-absorbing beams.

The original East Bay span, which is crossed by about 280,000 cars and trucks a day and has undergone a temporary retrofit, was built to handle about 4 inches of motion.