ORIGINAL EAST SPAN DEMOLITION
Crews have begun to carefully dismantle the 77-year old East Span section-by-section, in roughly the reverse order of how it was built in the mid-1930s.
Demolition of the nearly 2-mile long original East Span will take place in three phases over three to five years. Crews will first work in the westward direction toward Yerba Buena Island, taking apart the cantilever section and demolishing the S-Curve, before moving east to dismantle the 504’ and the 288’ truss spans. The demolition team will then head to the waterline to remove the piers, pilings and foundations that support the span. When the entire demolition project is complete, over 58,000 tons of steel and 245,000 tons of concrete will have been removed.
PHASE ONE: SEPARATING AND DISMANTLING THE CANTILEVER TRUSS TO YERBA BUENA ISLAND
The first phase of the demolition process: Cut the cantilever section at its center and begin dismantling both sides.
This work is well underway, with a 800-foot gap in the middle of the cantilever span easily visible from the new East Span. The 576-foot-long middle (suspended) section of the cantilever has been completely removed.
Before the demolition team cut through the cantilever and separated its two halves, preparations were made to reduce structural tension and pull the suspended span on each end toward the rest of the bridge. Without these precautions, the two halves would have collapsed and fallen into the water below.
Crews have also begun to demolish the temporary bypass known as the S-Curve. This section of the original span along is being cleared first in order to allow contractors to complete the bicycle and pedestrian path and to construct the permanent eastbound on-ramp from Yerba Buena Island.
PHASE TWO: DISMANTLING THE TRUSS SPANS
During the second phase of the demolition process, crews will remove the bridge’s truss section, which stretches east of the cantilever to the Oakland shore, and includes five 504-foot segments and 14 288-foot sections. Caltrans will advertise the contract for this work in July 2014.
PHASE 3: REMOVING UNDERWATER FOUNDATIONS
Crews will head beneath the structure to remove the underwater foundations that support the original span. Demolition contractors will remove the piers and pilings to the waterline and then extract the foundations down to the mud line. This contract will be advertised in late 2014.
Removing one member from a truss bridge can change the loads on other members, possibly creating a dangerous spring-action effect.
To figure out the best way to remove high-tension pieces, engineers are using a 3-D finite element computer program model based on structural analysis and historical records that shows how the forces are distributed.
During demolition, the team will monitor the state of the span via a system of 90 retroreflector prism targets installed at key locations on the bridge. As steel members of the bridge are removed, the updated target locations will be determined and entered into a computer system. This data will be compared up against the predicted locations in the finite element model software.
Though the new East Span is now open to the public, the environmental work is not done. Extensive monitoring and mitigation efforts will continue well into the future, as the environmental team works alongside demolition crews to ensure the safe dismantling of the original East Span.
DEMOLITION BY THE NUMBERS
Length of East Span – 1.97 miles
Total steel – 58,209 tons
Total concrete – 245,470 tons
Bridge steel – 51,687 tons
Pier/foundation steel – 6,522 tons
Bridge concrete – 66,962 tons
Pier/foundation concrete – 158,470 tons