WCA MAY 2015

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46 Wire & Cable ASIA – May/June 2015
From the Americas
Steel
More trouble for the San Francisco Bay
Bridge: indications of corrosion in one of
some 400 hard-to-access fasteners
“There is no obvious workaround for the rods that anchor
the 525-foot tower to its foundation. They were essentially
fixed in place when the tower was lowered atop them
during construction in 2010.”
San Francisco Chronicle staff writer Jaxon Van Derbeken
was referring to the 400-plus galvanised steel fasteners
at the base of the eastern-span tower of the bridge that
crosses San Francisco Bay between Oakland and Yerba
Buena Island.
On 20th February, Bay Bridge officials said that tests on
a 25-foot-long steel anchor rod removed after being
inadvertently submerged in water for years disclosed
rust and tiny cracks – a potentially worrisome sign for the
long-term viability of the self-anchored suspension bridge.
The rods, which sat in holes at the tower’s foundation that
were poorly grouted, cannot be removed without being
destroyed. And there is not room enough for manoeuvring
replacement rods into position.
Thus any evidence of water damage to the rods presents
Caltrans – the California Department of Transportation
– with what the Chronicle said “could be an unsolvable
dilemma.” (“Rust, Cracks Found on Bay Bridge Tower Rod,”
20 th February)
That makes this latest in a series of construction problems
on the $6.4 billion bridge potentially one of the most
serious. Wrote Mr Van Derbeken: “Other steel rods that
stewed in rainwater for several years snapped when they
were tightened in 2013 on seismic-stability structures on
the bridge, but Caltrans was able to engineer a replacement
for them.”
At a news conference in Oakland to announce the results
of preliminary tests on the removed rod, Caltrans bridge
engineer Brian Maroney said that a plan of action on the
new problem must await further test results.
“I want to know what I’ve got down that hole to make a
good decision,” Mr Maroney said. “We’re still in the process
of the science.”
A corrosion risk: but how great?
The rods are coated in zinc – galvanised – for rust
resistance. But galvanisation can make metal more
vulnerable to another form of corrosion: hydrogen-induced
cracking. The Caltrans tests revealed that the galvanising
layer was gone on parts of the rod, an indication that
hydrogen may have invaded the metal.
Mr Van Derbeken recalled that hydrogen-induced cracking
was implicated in the failure of 32 galvanised rods on the
bridge in 2013.
Officials downplay that risk in the current episode, on
grounds that the tower rods are under less tension than
those in the seismic-stability structures that gave concern
earlier.
In Mr Maroney’s view, the discovery that other rods at
the tower base are cracked and rusted would not present
“a safety issue.” Even if many of the rods were to fail in a
large earthquake, he said, it would inflict extra damage on
the tower – but not catastrophic failure.
Others are less certain. Two independent experts consulted
by the Chronicle said that, because tiny cracks like those
found on the tested rod can worsen over time, the tower
rods are at risk of failing even at their lower levels of stress.
“If it started, it will grow,” said Yun Chung, a retired Bechtel
engineer and expert on steel fasteners who has been
critical of Caltrans. “It will continue to grow until reaching a
critical size – then, bang.”
Lisa Fulton, a metallurgical engineer and materials scientist
who specialises in corrosion, told Mr Van Derbeken that the
loss of the zinc galvanisation coating is telltale evidence
of the electrochemical reaction that drives hydrogen from
standing water into high-strength steel. As with the rods
that failed on the span in 2013, the presence of hydrogen
can make the steel vulnerable to failure, Ms Fulton said.
 According to the account in the Chronicle, Caltrans said
many of the rods sat in only a few inches of moisture;
but 60 or so were entirely submerged in water that got
into the tower during storms and power-washings.
Engineers cut apart and removed two of those for
testing.
The first rod was tested only for its material properties.
The second rod to be removed was tested more
extensively and showed rust and cracking.
Caltrans officials have said that the main bridge
contractor, Oakland-based American Bridge/Fluor
Enterprises, did not follow specifications that called for
the sleeves surrounding the tower rods to be filled with
moisture-resistant grout. The company – a joint venture
of American Bridge Co (Coraopolis, Pennsylvania) and
Fluor Corp (Irving, Texas) – is removing standing water
from the sleeves and putting in new grout.
Energy
Their revenue squeezed by slowing
growth in demand for electricity,
USA utilities eye the electric vehicle
charging business
Since their commercial introduction some five years ago,
electric vehicles have failed to significantly penetrate the
US mass market; largely, experts say, because an adequate
network of public charging stations has not been built. But
now, according to New York Times energy reporter Diane
Cardwell, that could change – if major electric utilities have
their way.
BigStockPhoto.com Photographer: Aispl