EoW July 2013

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July 2013 18
Bay Bridge’s broken bolts
For the problematic eastern span of the
new San Francisco-Oakland Bay Bridge,
an elusive x and blame to go around
State senators on 14th May pressed California Department
of Transportation (Caltrans) o cials at a hearing on their
plans for dealing with suspect steel parts in the new San
Francisco-Oakland Bay Bridge. “I understand that this is a
big project, but we seem to have problem after problem
after problem,” one of the senators said to Caltrans director
Malcolm Dougherty.
Whether the bridge will open to public tra c, as planned, on
Labor Day (2nd September), depends heavily on how quickly
a retro t can be completed to replace the function of 32 bolts
that broke in March after being tightened down by contractors.
Caltrans and other agencies have struggled to determine a x
for the broken bolts – also known as rods.
On 23rd May, o cials overseeing construction of the bridge
presented an update on a plan, previously announced by the toll
bridge programme oversight committee, to compensate for the
broken bolts by installing large steel saddles over two seismic
safety devices on the span. And the o cials themselves received
an update: about ongoing testing of the other xtures on the
bridge.
Reporting from Oakland in the Contra Costa Times (22nd May),
Lisa Vorderbrueggen wrote that the use of large galvanised
steel fasteners on a project in 2001 – the retro t of the
Richmond-San Rafael bridge – had led engineers to adopt the
same speci cations for the bolts that snapped this year on the
Bay Bridge.
Weakened molecular structure
Noting “the well known phenomenon” of weakened molecular
structure in high-strength steel coated with zinc, with attendant
risk of embrittlement and fractures, Ms Vorderbrueggen wrote,
“National standards caution engineers about [the use of
galvanisation], and the Caltrans bridge design manual prohibits
it on ordinary spans.”
Referencing dozens of documents, emails and letters released
by Caltrans, the Times reported that – in designing the unique
self-anchored suspension span for the Bay Bridge in 2003 – state
and private engineers believed that modi cations in steel rod
manufacture, developed for the Richmond-San Rafael retro t,
would su ciently reduce the risk of hydrogen embrittlement.
The adaptation “does the trick for galvanising high-strength
rods,” a Caltrans engineer told colleagues in April 2003 – an
assurance that, ten years later, would prove faulty. In early
March, a third of 96 high-strength threaded rods – three inches
in diameter and 17 to 24 feet long – broke in key seismic
stabilisers on the Bay Bridge span.
Ms Vorderbrueggen wrote: “Engineers blame hydrogen
embrittlement triggered by the combination of susceptible
steel, the presence of hydrogen atoms trapped during
galvanising, and the heavy load on the fasteners.”
† Caltrans, Bay Area Toll Authority, the bridge contractor, and
the team of private engineering consultants hired to design
the span are now striving to determine whether a proposed
$5 million to $10 million repair job can be nished in time to
open the bridge on schedule.
Steel
Drop in American and European crude
steel production is more than o set
by higher Asian output, especially in China
The most recent data from the Brussels-based World Steel
Association showed global crude steel production rising 1.2 per
cent in April compared with April 2012, as higher output from
Asia – notably China – contrasted with declining output in other
major steel producing regions.
Worldsteel on 21 st May reported that global production rose
to 132.1 million tons in April compared with 130.5 million tons
in the same month of last year, while crude steel production in
China, the world’s largest steel producer, increased 6.8 per cent
year-on-year to 65.7 million tons. Japanese and Indian steel
production also rose, 1 per cent and 3.5 per cent, respectively,
o setting declines in South Korea and Taiwan.
Excluding China, production in the rest of the world declined 3.7
per cent year-on-year in April to 66.5 million tons, according to
data from the 63 countries contributing to the report. Worldsteel
member-states account for some 85 percent of global steel
output.
North American crude steel production fell 5.7 per cent
year-on-year in April to 10.1 million tons, driven by a 7.3 per
cent drop in US crude steel production to 7.3 million tons. South
American steel production dropped 3 per cent compared with
April 2012, to 3.9 million tons, as Brazilian crude steel production
fell 1.6 per cent to 3 million tons.
Transatlantic Cable
Image: www.bigstockphoto.com Photographer Zsolt Ercsel