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
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
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
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.