WCA MAY 2015

From the Americas

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.

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 20 th 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.

BigStockPhoto.com Photographer: Aispl

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Wire & Cable ASIA – May/June 2015

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