On July 8, the Toll Bridge Program Oversight Committee (“TBPOC”) announced that the opening of the new East Span of the San Francisco-Oakland Bay Bridge has been postponed. In mid-July 2005, Governor Schwarzenegger and the State Legislature, through Assembly Bill 144, created the TBPOC to provide project oversight and project control for the Bay Area’s Toll Bridge Seismic Retrofit Program, which includes the San Francisco-Oakland Bay Bridge East Span Replacement Project. The TBPOC’s project oversight and control activities include: (a) reviews of contract bid documents and specifications, ongoing capital costs, significant change orders and claims; (b) implementation of a risk management program; and (c) resolution of project issues.
As part of the TBPOC’s charge, it is investigating and resolving the challenge of the fractured A354 grade BD high-strength steel rods/bolts installed on the Self-Anchored Suspension (SAS) Bridge of the new East Span. 32 of the 96 A354 grade BD high-strength anchor rods on shear keys S1 and S2 on Pier E2 failed in March 2013 after being tightened to their specified tension levels. In response, TBPOC launched an investigation into why these rods failed and whether the 2,210 other rods on the SAS Bridge also are at risk. The TBPOC directed its staff to investigate and report on what led to the failure of the rods, what course of action is needed to address all the rod failures, and what implications the analysis, findings and recommendations from the investigation have on the TBPOC’s determination of the timing for opening the new East Span to traffic.
On the same day that it announced the delay in completion of the bridge, TBPOC released its 102-page Report on the A354 Grade BD High-Strength Steel Rods on the New East Span of the San Francisco-Oakland Bay Bridge With Findings and Decisions. The Report’s Summary of the TBPOC Investigation concludes that “Hydrogen embrittlement is the root cause for the failure of the A354 grade BD high-strength steel anchor rods at shear keys S1 and S2 (Item #1 in Table ES-1). As used in this report, hydrogen embrittlement is considered a short-term phenomenon that occurs in metals, including high-strength steel, when three conditions apply: a susceptible material, presence of hydrogen and high tensile stress (as shown in Figure ES-4). To trace what led to the rod failures, this summary calls out each of the three hydrogen embrittlement conditions, and then tracks the events and decisions that either caused or contributed to that condition. In their totality, these events and decisions led to the failure of the 2008 A354 grade BD rods in March 2013.” The Report discusses what retrofit strategy should be used to replace the lost clamping force of the rods, including that, after review of three retrofit design options, the “TBPOC unanimously approved selection of the steel saddle retrofit option after finding that it would meet all design requirements and objectives of the project. As shown in Figure ES-5, it also applies a direct preload to the lower housing via the radial forces that are developed from the main vertical post-tensioning force being applied as intended in the original design.”
It also reports that “[a]s for the remaining 2,018 A354 grade BD rods, none have failed, and all have been under tension from 91 to 1,429 days as of July 1, 2013. Because hydrogen embrittlement is a time-dependent phenomenon, also dependent on the level of sustained tension, these rods have low risk of hydrogen embrittlement. In contrast, approximately 30 percent of the anchor rods in shear keys S1 and S2 failed just 3 to 10 days after tensioning to their design loads, and more might have failed if that tension level had been maintained.” However, “[t]he longer-term concern is whether the remaining A354 grade BD rods are susceptible to stress corrosion cracking and, if so, when cracking may occur. Like hydrogen embrittlement, there are three factors that contribute to stress corrosion cracking — susceptible material, high tensile stress and hydrogen-related corrosion. Without any one of these three conditions, stress corrosion cracking will not occur.” The Report confirms that “[f]urther, stress corrosion testing is underway as part of Tests IV and V that will provide important data for further analysis and remediation of the rods.” To read the Report, click here.
There was a public briefing at a special meeting of the Bay Area Toll Authority on July 10 at 10 a.m. at the Metropolitan Transportation Commission offices at 101 Eighth Street in Oakland, Calif. Discussions took place and questions from the public, elected officials and the media were answered by members of the TBPOC and by members of the Seismic Safety Peer Review Panel. To hear the online audio-cast, click here.