LOS ANGELES Dyson Corp. has said that an analysis of steel anchor rods it made for the San Francisco-Oakland Bay Bridge "exonerates" the company on the failure of several of the rods.
"We made the product exactly to the specifications that they asked us," Dustin Johnson, director of sales at the Painesville, Ohio-based fastener systems fabricator, told AMM May 17.
Dyson, which supplied the rods to bridge contractors American Bridge Co., Corapolis, Pa., and Fluor Corp., Irving, Texas, had previously declined to comment (amm.com, April 1).
In March, 32 out of 96 galvanized ASTM A354 grade DB rods manufactured by Dyson in 2008 broke when they were tightened to connect shear keys, or seismic safety devices, on the bridges new east span.
Johnson pointed to a metallurgical analysis of the rods recently done for the California Department of Transportation (Caltrans) that concluded the failures were caused by "higher than normal susceptibility of the steel to hydrogen embrittlement," and that the rods "comply with the basic mechanical and chemical requirements of ASTM A354 grade DB."
A San Francisco Metropolitan Transportation Commission spokesman couldnt comment on Dysons claim.
Johnson, who stressed that "we do not design or engineer" the rods, said he couldnt comment on who is responsible for the failure. "Our customers give us the specifications and we make parts to these specifications."
Meanwhile, a second group of 192 steel anchor rods fabricated by Dyson in 2010 for a new section of the bridge so far havent shown the same problems seen with the 2008 batch, Bay Area Toll Authority executive director Steve Heminger said.
A determination on whether the 2010 rods will be replaced is expected by the next meeting of Californias Toll Bridge Program Oversight Committee on May 29, he said.
"We believe we will be able to give you a decision" on the 2010 anchor rods at the meeting, according to Heminger, who also heads the oversight committee.
The 2010 anchor rods have so far shown "no signs of failure" after tightening, unlike the 2008 rods that broke "within days of being tightened," the committee said recently, noting that it continues to conduct "a battery of tests to confirm integrity."
As additional data comes in from rods that have been "pulled" from use and subjected to destructive testing, engineers have seen "significant differences" between the metallurgical qualities of the 2010 rods and those supplied in 2008, the transportation commission spokesman said. On average, the 2010 rods show a greater degree of toughness, making them "less susceptible to hydrogen embrittlement," he added.
Meanwhile, the committee noted that large steel saddles will be installed over two seismic safety devices following the March failure of the 2008 anchor rods, costing $5 million to $10 million.
It hasnt yet been determined whether the saddles fabrication and installation will affect the new spans opening, scheduled for Sept. 3, according to officials testifying before the toll authoritys oversight committee.