OAKLAND -- Bay Bridge officials are pursuing a short-term fix for the new eastern span that could give them an option to open it as planned on Sept. 3.
Given that officials just days ago said the opening would be delayed by weeks or months, nobody is willing to say that they are likely to reverse course just yet. But the Bay Bridge construction oversight team is asking the Federal Highway Administration to evaluate a proposal to install temporary shims in four bridge bearings adjacent to the seismic stabilizers where bolts snapped in March. While the federal peer review is advisory, the request signals the Toll Bridge Program Oversight Committee could reconsider its decision to hold off on the planned post-Labor Day traffic switch if federal engineers bless the wedge plan.
"Since the bearing shim proposal may offer the possibility of achieving seismic safety on the (new bridge) before the completion of the shear key retrofit, time is of the essence in the completion of your review," wrote Steve Heminger, oversight committee chairman.
Caltrans was already planning to install the temporary shims as a seismic safety measure while permanent repairs were being done, but they never intended to use them as leverage in the fierce debate over when to open the new bridge.
They saw the insertion of painted steel wedges and plates into the rocker assemblies -- restricting their normal back-and-forth movement -- as an interim way to protect the bearings from damage if an earthquake strikes before the shear key retrofit is finished in December.
But the shims would also shore up the span's seismic strength and allow it to open while the repairs continue, Toll Bridge Program Seismic Safety Peer Review Chairman Frieder Seible told the Bay Area Toll Authority in a surprise pitch on Wednesday.
Locking down the four bearings allows them to engage simultaneously with the remaining two functioning shear keys during a temblor and compensate for the lost rods' holding power, he explained.
"The contractors have the designs in front of them, and as soon as we shim (the bearings), we will still achieve the full seismic safety of the bridge, and we can do it within a month's time," said Seible, a retired UC San Diego engineering school chairman who has advised California on seismic safety for a quarter of a century.
On Friday, the oversight committee formally asked Federal Highway Administration to look at the idea. Outside peer review requests have become commonplace on the high-profile bridge where for the last decade, every construction challenge, real or routine, is subject to great public scrutiny.
"The (committee) said they would take this into consideration, and the letter is a reflection on moving forward on that consideration," said Bay Bridge spokesman Andrew Gordon.
There is no set timeline for when the oversight panel will make a decision. The committee consists of Heminger, also executive director of the Metropolitan Transportation Commission, Caltrans Director Malcolm Dougherty and California Transportation Commission Executive Director Andre Boutros.
To understand how the bearings and shear keys work, picture the rocker bearing as a pair of men's suspenders and a shear key as a belt.
The suspenders are a bit loose so he can move but the belt is cinched tight so his pants stay up.
On the bridge, the bearing, or "suspenders," move back and forth with traffic loads and temperature changes. The shear key, or the "belt," clamps together the bearings, columns and deck, and keeps them aligned during an earthquake.
But with two of the four shear keys out of service due to the broken bolts, the bearings are exposed.
The shims may be a good insurance policy for the bearings, but Seible has repeatedly said the bad shear keys are unnecessary for day-to-day traffic operations. And given the known vulnerability of the existing 1936 eastern span, he has for years urged the Bay Area to open the new bridge without delay.
Caltrans bridge engineer Brian Maroney concurred with Seible in the engineering analysis sent to the Federal Highway Administration.
The data "overwhelmingly drives a shift of public traffic to the replacement bridge from the old bridge based on a desire for public safety ... as soon as feasible," Maroney wrote.
Even without the two functioning shear keys, the pier where the bolts broke is designed to meet California's most stringent seismic standards, which would allow the bridge to reopen within hours of the largest earthquake seismologist expect in the next 1,500 years.
Engineers evaluated shims in the weeks immediately after 32 out of 96 very large steel anchor rods snapped. It was a catastrophic failure that triggered the need for a retrofit expected to cost as much as $20 million and further delayed a bridge that is already 10 years late.
At the time, Caltrans and TY Lin/Moffatt & Nichol engineers set aside the temporary shims and focused instead on a permanent fix. They settled on an exterior steel saddle and cable assembly that will replace the loads intended for the rods.
As the retrofit timeline dragged out, engineers worried about bearing damage if a temblor hit before the shear keys were back in service.
The span has four shear keys and four bearings inside the pier cap. The bolts broke in the keys positioned immediately over the two columns. A bearing flanks two sides of each key over a column.