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Corrosion likely culprit in roof collapse

The partial collapse of a shopping mall roof last weekend was likely the result of a combination of factors the most likely cause was corrosion of the reinforced concrete, said Mark Green, a Queen’s University engineering professor.

On Saturday afternoon a section of the roof at the Algo Centre Mall (Kingston, Ontario) collapsed.

A section of roof about 12 metres by 24 metres fell.

The roof supported a parking lot and at least two vehicles fell into the mall when the roof came down. Because the roof served as a parking lot, corrosion could have been an even greater issue because of the salt used to clear the surface of ice during winter.

Green said it was also possible that the design of the building may have included an aspect that made it more susceptible to collapse.

Twenty-two people were injured in the collapse.

Police also said at least 30 were missing.

In 2010, mall owners Eastwood Malls Inc. spent about $1 million to repair leaks in the roof that had been ongoing for several years.

But hints of a catastrophic collapse may have been easily overlooked, Green said.

“The warning signs may not have been that obvious,” he said.

In April 2010, a section of the parking garage at Confederation Place hotel in Kingston collapsed, damaging about 20 vehicles and closing the hotel for several days for repairs.

In 2006 a bridge in Laval collapsed, killing five people. That bridge had been inspected shortly before it fell, Green said

That bridge collapse prompted inspections of other bridges in Quebec and Green said he expects buildings similar in age and design to the Algo Centre to undergo additional inspections in the coming weeks.

On Monday a small piece of concrete fell off the Gardiner Expressway hitting a car below.

SOURCE: http://www.thewhig.com/2012/06/25/corrosion-likely-culprit-in-roof-collapse-expert

Caissons a solid sign of progress on new Forth bridge

The new Forth crossing will be fitted with dehumidification equipment to cut the risk of the corrosion which has blighted the existing bridge.

At a briefing on the progress of the £1.4 billion project being built by the Forth Crossing Bridge Constructors, Transport Scotland project director David Climie said work was on schedule.

”We are still exactly where we want to be, on time and budget,” he said.

Only three months ago there were 384 people working from the Rosyth base but now that number has more than doubled, with 800 staff working on various parts of the site. At its peak 1,200 staff will be employed.

One of the most important milestones of the entire project has just been reached — the arrival of the first two caissons which will form the foundations of the north and south towers.

In a ”foundation” year for the project, Mr Climie said: ”We are extremely happy with the way things are progressing.”

Carlo Germani, the FCBC project director, said: ”We are into the real construction work now. We have done a lot of the preparation and what you see is work on the bridge itself starting with the arrival of the caissons.”

These are the huge cylinders ranging in height from 21.1m to 30m — around the same as an eight-storey building — with diameters of around 32m.

The largest weighs roughly 1,200 tonnes, making it one of the largest steel caissons ever sunk down to the seabed.

They will be used as moulds for the foundations, comprising underwater and reinforced structural concrete. More caissons are due to arrive in a few days.

FCBC’s Carson Carney explained the process of building the central tower, which will be constructed on site in 4m high increments, would start this year.

The deck sections are being built in China and Spain and will be shipped over and stored at Rosyth.

With corrosion affecting the existing bridge, Mr Carney explained the crossing’s cables are made up of strands containing galvanised steel wires, with a wax coating and covered in plastic.

”There is no way you can get water into the actual strands themselves. This is a state-of-the-art type system.”

Each strand is capable of being individually replaced if necessary without causing widespread disruption to traffic.

There is a dehumidification system at deck level and on the anchorage points.

SOURCE: http://www.thecourier.co.uk/News/National/article/23358/caissons-a-solid-sign-of-progress-on-new-forth-bridge.html

Road cave-in caused by corrosion in slab

MUMBAI: The Andheri (E) road cave-in on Tuesday was caused by corrosion of steel in a slab, it has been revealed prima facie.

Consultant D S Joshi, who made the submission to the BMC, told TOI that material from the site had been sent for laboratory tests to ascertain the reasons for the corrosion. “I would be able to give the exact reasons once the report is available. It would take about a week,” he added.

Meanwhile, the BMC on Wednesday decided to conduct an audit of all concrete slabs over nullahs across the city.

The 30-ft road in Gundavali village has two lanes on either side of a 20-ft-wide nullah. The road was built by laying slabs atop portions of the nullah in 1985.

N V Merani, chairman of the Standing Technical Advisory Committee (STAC), said the nullah’s water could have eroded the earth below the slabs. “The other possible reasons could be lack of maintainance or poor quality,” he said, adding that laboratory results could only shed light on the extent of loss of strength due to corrosion and not the reasons behind the same.

“This can be found out only through close inspection of the corroded section by an experienced engineer,” he said.

Two weeks ago, the STAC had raised the issue of old civic bridges with the BMC. There are 253 bridges in the city; of these, 102 are over waterways, 17 are flyovers, 41 road overbridges, 93 foot over-bridges and subways.

“We did a study of 34 old bridges three years ago. By now, they should have been repaired or reconstructed. But nothing has moved,” said Merani.

The STAC had recommended that a separate chief engineer be appointed to exclusively monitor bridges and concrete roads. The BMC has created a post not filled it up. “The MMRDA is constructing flyovers and roads and handing them over to the BMC. The corporation needs to appoint a person to that post. We have even suggested that if they cannot promote an engineer, they can get someone on deputation. But decisions in the BMC are ad-hoc,” he said.

SOURCE: http://articles.timesofindia.indiatimes.com/2012-05-24/mumbai/31839803_1_bmc-slabs-bridges

Golden Gate celebrates 75th with help of engineers

The Golden Gate Bridge was heralded as an engineering marvel when it opened in 1937. It was the world’s longest suspension span and had been built across a strait that critics said was too treacherous to be bridged.

But as the iconic span approaches its 75th anniversary over Memorial Day weekend, the generations of engineers who have overseen it all these years say keeping it up and open has been something of a marvel unto itself.

Crews had to install a bracing system after high winds lashed and twisted the span in the 1950s, raising fears it would collapse. Years later, they had to replace vertical cables when they were found to have corroded in the bridge’s damp, foggy climate, potentially destabilizing the span.

The bridge, which rises majestically above a Civil War era fort on the San Francisco side and arches across to the Marin County headlands on the north side, is currently in the midst of a seismic upgrade that has seen many of its key structures replaced or modified. Plans for a moveable barrier to separate north and southbound traffic and a net system to prevent suicides are also moving forward.

“When (one of the bridge’s designers) made his final speech during opening day ceremonies in 1937, he said, ‘I present to you a bridge that will last forever,'” said Daniel Mohn, the bridge’s former chief engineer, who co-authored a book about the span. “What he should have said is, ‘I present to you a bridge that will last forever if properly maintained.'”

The idea for a bridge across the Golden Gate strait, where San Francisco Bay meets the Pacific Ocean, was championed by the engineer Joseph Strauss in the 1920s. Strauss’s original design, submitted to San Francisco city officials in 1921, called for a hybrid cantilever-suspension bridge. The idea for a full-suspension span — the design that was ultimately built — came later.

At a little more than three-fourths of a mile in length, the Golden Gate Bridge would become the world’s longest suspension span.

It had to be light enough to hang from its own cables, but still strong enough to withstand the strait’s fierce winds and the possibility of earthquakes. Some said it was impossible.

Engineers also had to calculate all the potential forces on the bridge without the help of computers.

“In those days, you had (notebooks) and a number two pencil and you wrote it out, did all the math at your desk,” said Kevin Starr, a history professor at the University of Southern California, who has also written about the bridge.

Eleven men died during construction from 1933 to 1937 — ten of them when scaffolding fell through a safety net that had been set up to protect workers.

The conditions were difficult, cold, foggy and windy, and workers who helped construct supports for the south tower had to contend with dangerous tides.

But it was the wind that would continue to vex engineers years after the bridge’s completion. In 1951, it was closed for several hours when wind gusts approached 70 mph and caused the bridge to flutter.

It was twisting so badly, Mohn recalled during a recent phone interview, that the light standards at the center of the span were striking the main cables.

“It sure almost destroyed the Golden Gate Bridge,” he said. The Tacoma Narrows Bridge in Washington — a suspension bridge whose designer also worked on the Golden Gate — had twisted and snapped in about 40 mph winds a little more than a decade earlier. That 1940 collapse was captured on film.

Although the Golden Gate Bridge had stiffening trusses that made it less susceptible to wind, it did sustain damage, Mohn said.

Officials decided to add lateral bracing that made the trusses more stable and reduced the chances of the bridge going into a potentially catastrophic twisting motion.

The bridge would be able to withstand winds of 70 mph today although the goal is to eventually increase its tolerance to 100 mph, according to Ewa Bauer, the bridge’s current chief engineer.

The wind is not the only element to take its toll on the span. The damp, foggy air has also kept its painters and engineers busy.

“You couldn’t have put the bridge in a more corrosive atmosphere than in the middle of the Golden Gate with that salt fog coming in,” Mohn said.

Engineers discovered in the 1970s that the bridge’s suspender ropes — the vertical cables that connect the deck to the main cables — had corroded, some so badly that they could be picked apart with a pocket knife.

The problem in part, Mohn said, was that bridge maintenance had been neglected for many years, particularly during World War II. A design flaw also hastened corrosion.

All of the cables were replaced in the mid-1970s.

There was another scare on the bridge during its 50th anniversary in 1987 when an estimated 300,000 pedestrians gathered on the span, which was closed to vehicle traffic.

The weight of the crowd flattened out the arch of the bridge deck and caused some revelers to suffer motion sickness as the bridge swayed.

Although the bridge supported its heaviest load in 50 years that day, Mohn would later conclude the weight and movement had not exceeded its design capacity.

Today, among the engineers’ most pressing concerns is the potential effect of a major earthquake.

The 1989 Loma Prieta earthquake, which occurred during a live broadcast of the World Series, caused two 50-foot sections of the San Francisco-Oakland Bay Bridge to collapse.

The Golden Gate Bridge was not damaged. But the quake still spurred bridge officials to undertake a massive retrofit of the span — a $660 million project that began in 1997 and is still underway.

Bridge pylons have been reinforced with steel and towers under the bridge’s two approaches were replaced, all while keeping the bridge open and its appearance unchanged. Retrofitting the suspension span is the project’s final phase although experts say its flexibility makes it less vulnerable in an earthquake.

“If I knew when an earthquake was coming, I’d get to the suspension span of the Bay Bridge or the Golden Gate Bridge,” said Abolhassan Astaneh-Asl, an engineering professor at the University of California, Berkeley who studied the Golden Gate Bridge after Loma Prieta. “They are safest places to be.”

The goal is to withstand an 8.1-magnitude earthquake when the retrofit is completed years from now.

The bridge district is also moving forward with plans for a steel net below the span to prevent suicides.

The Golden Gate Bridge has long lured people looking to end their lives. More than 1,200 people have plunged to their deaths from the span since it opened.

The bridge’s board of directors approved the net system in 2008. Funding for the project, which is estimated to cost tens of millions of dollars, has not yet been secured but work on its final design is underway.

The bridge, like other infrastructure, has a lifespan. But Bauer and Mohn say with proper maintenance, the Golden Gate Bridge will endure. The retrofit project alone will buy the span another 150 years, Bauer estimated.

“I believe the bridge was built to absolute great standards of workmanship,” she said on a recent morning at a vista point overlooking the span. “What we are doing right now is repairing…and you can truly do it indefinitely.”
SOURCE: http://www.foxnews.com/us/2012/05/21/golden-gate-celebrates-75th-with-help-engineers/#ixzz1vbw4i0C0

Hammersmith tunnel ‘solution to crumbling flyover’

A west London council has said building a tunnel is the long-term solution to replace a “crumbling” flyover.

The Hammersmith Flyover has been under repair works since December and is scheduled to reopen fully on 30 May.

Hammersmith and Fulham Council said: “We must continue to push for an alternative solution, and that is a tunnel.”

Transport for London (TfL) said the flyover “would be able to survive for several further decades”.

A council spokesman said: “TfL must realise that we cannot simply accept patch-jobs to prolong the life of this monstrous outdated and crumbling structure.”

TfL Surface Transport spokesman Garrett Emmerson said: “Our engineers, contractors and traffic control operators continue to work flat out to deliver a permanent fix to the Hammersmith Flyover well ahead of the 2012 Games.

“The structure would be able to survive for several further decades.

“However the Mayor has also asked us to consider long term options for the area and that work will consider a range of possible solutions to the area’s future needs.”

The strengthening works, which began in January, have seen about 200m (650ft) of the central reservation along the flyover removed, a new structural slab and concrete barriers installed, as well as tailored anchorages for the new cables installed within the structure.

TfL has been carrying out two weeks of overnight closures to flyover since 15 May to carry out the final parts of this work.

It said it would return to the structure in 2013 for more strengthening work which will be carried out, where possible, with no weight or lane restrictions and minimal closures to the flyover.

SOURCE: http://www.bbc.co.uk/news/uk-england-london-18095448

Anthony Wayne Bridge (Ohio) to close in 2013 for 2 years

Toledo’s Anthony Wayne Bridge will be closed to all traffic for two years, likely to start sometime in 2013, as part of a three-year, $50 million overhaul of the 81-year-old structure by the Ohio Department of Transportation.

The fundamental main-span appearance of the bridge — which carries State Rts. 2, 51, and 65 over the Maumee River and is the last suspension bridge on Ohio’s state highway network — will not change. The first approach span on either side of the suspension spans will be completely replaced during the project with new two-span structures.

Deck replacement on all the other spans is planned, along with joint improvements, cable repairs, and corrosion removal on the bridge’s steel girders, said Theresa Pollick, a department spokesman in Bowling Green. A separate painting contract will be issued after all structural and deck work is done.

The shutdown will be required because of the complete replacement of the two approach spans, Ms. Pollick said.

The spans to be replaced, which have deck-truss designs, are “fracture critical,” meaning that if certain parts of their structures were to break, they lack the backups necessary to prevent a collapse.

“The closure duration is necessary for the amount of work we must do and for the safety of those who travel the bridge during construction,” said Todd Audet, the transportation department’s district deputy director.

As the last suspension bridge on the state system, he said, “it’s important to ODOT to preserve it.”

The Anthony Wayne Bridge — also known locally as the High Level Bridge — gained its distinctive status on Feb. 22 when the transportation agency dynamited the Fort Steuben Bridge over the Ohio River between Steubenville, Ohio, and Weirton, W.Va. No other suspension bridges still standing in Ohio, or across the Ohio River, are part of the state system, the agency said.

The Anthony Wayne bridge last underwent major repairs in 1997 and 1998, when its concrete deck was resurfaced, some steel suspender cables were replaced, its main suspension cables were wrapped with weatherproofing material, and other repairs were made.

SOURCE: http://www.wtol.com/story/17457960/aw-trail-bridge-to-close-in-2013-for-2-years

Corrosion Work on George Washington Bridge will take 10 years

Peter Zipf sounds more cardiologist than civil engineer when he talks about subjecting the George Washington Bridge to the equivalent of the classic battery of tests for heart disease and finding the first signs of plaque.

“It really is a little like giving somebody an EKG and checking their cholesterol levels,” said Zipf, the Port Authority’s chief engineer. “There are certain things you know you have to watch for, to catch them before they go too far.”

And chief among those certain things, as a bridge ages, is the corrosion that can sap the strength of its steel.

“Moisture is the big culprit,’” continued Zipf. “You have to constantly monitor the amount of corrosion and the rate of deterioration, and then determine when to intervene.”

The GWB’s test results have spurred the Port to intervene now and undertake the biggest rehabilitation in the 81-year history of the world’s busiest bridge. When the work is completed in 2022 – yes, 10 years from now – the Port will have spent $1.5 billion, a piffle in comparison to the $6-billion-to-$8-billion that it would cost to build the GWB today.

The centerpiece of this your-tolls-at-work program will be the first-ever replacement of the GWB’s suspender ropes, all 592 of them. The ropes, vertical bundles of woven steel wire that attach to the four main cables and support the deck, will be replaced a couple or three at a time to keep the 600,000-ton bridge on an even keel.

To assist, the Port, fittingly, has hired Ammann & Whitney, the consulting engineering firm founded by Othmar Ammann, the man who designed and built the GWB and five other suspension bridges in the city.

The Port will also rehabilitate the upper level’s deck (work already in progress), remove the lower level’s original, and failing, lead paint, rebuild the 177th and 178th Street ramps as well as the multiple ramps to the GWB bus station and repair the Center and Lemoine Avenue bridges.

“The bridge can withstand this extreme work because it’s very robust in terms of strength – remember it was built to handle rail,” explained Zipf. “So that extra strength becomes a safety factor that gives the bridge the tolerance for rehabilitation.”
(Careful readers will recall the Thruway Authority will spend more to build the new Tappan Zee Bridge strong enough to support rail – or serious rehabilitation in the next century, if rail is never added.)

Does any or all of this mean the bridge-and-tunnel crowd is doomed to construction delays at the GWB for 10 years?
“In all of our work, through design, staging of construction and so on, we strive to minimize the impact on traffic,” pledged Zipf. “We’ll only close a lane during off-hours or at night, so if you cross the bridge at rush hour, you aren’t going to be aware that anything’s going on.”

…For 10 years.


Big Dig needs $54 light fix – corroded tunnel fittings must be replaced

The state’s top highway official says all the light fixtures in the Big Dig tunnels must be replaced, a $54 million effort made necessary by design or manufacturing defects that have led to dangerous corrosion.

The project, expected to begin next year, will cause frequent lane closings in the tunnels for up to two years, a headache for motorists. The work will be done largely at night, with traffic diverted to surface roads.

Since a light fixture fell onto the northbound lane of the Thomas P. O’Neill Jr. Tunnel in February 2011, engineers have temporarily shored up the 8-foot light fixtures in the 7.5 mile tunnel system with plastic ties. Now, after a year of study, the state’s highway administrator, Frank DePaola, is recommending a complete overhaul, the most expensive of several alternatives.

“The preferred alternative is a complete replacement,’’ DePaola told the Massachusetts Department of Transportation board of directors Wednesday.

“The existing fixtures continue to corrode,’’ he said. “We could have more incidents. For that reason, I think it is best for all of us that we remove the fixtures.’’

“We just have to do it,’’ added Richard A. Davey, the state transportation secretary and DePaola’s boss, agreeing it is a safety issue.

Though the replacement project will be expensive, DePaola said the new fixtures offer opportunities for savings over the long term from energy efficiency. He said the more energy-efficient LED lights are expected to cost $2.5 million a year less in electric bills than the current fluorescent lights.

He also said the new fixtures will not be susceptible to the moisture that apparently caused the corrosion in the existing fixtures. The new light casings will be sealed plastic fixtures, rather than an assembly of removable component parts that require maintenance. When the new lights burn out, the entire fixture will be replaced, he said.

Money for the overhaul is expected to be drawn from a maintenance fund set up in 2008 with the proceeds from a nearly $500 million settlement with Big Dig contractors Bechtel/Parsons Brinckerhoff and others for shoddy work on the $15 billion project, which has been plagued by problems ranging from water leaks to a fatal ceiling collapse in 2006.

Before the state can begin the project, however, the transportation board must approve the plan. In addition, the federal government must approve use of the Big Dig settlement fund for the light replacement project.

Transportation officials still have not determined who is to blame for the corrosion that so weakened one fixture that it fell and left dozens of others badly compromised, DePaola said. They initially focused on the company that manufactured the lights, NuArt of California, but the company was bought out by another firm and discontinued years ago.

“We are working with our attorneys and engineering consultants to determine responsibility,’’ DePaola said, adding, “You can’t get damages from a company out of business.’’

If the state is able to recover damages, that money will be used to replenish the maintenance fund, which now has a balance of about $393 million, he said.

If the lighting plan is approved, as expected, tunnel closings related to the overhaul could begin in about a year, transportation officials said. Crews will close either the northbound or southbound side of the O’Neill Tunnel at 11 p.m. and reopen it at 6 a.m.

Closings will also be necessary at the Ted Williams and Interstate 90 Connector tunnels.

Such closings, however, have already begun in the O’Neill Tunnel for washing and other maintenance and will continue for about a year, transportation officials said.

Wednesday’s announcement caps a turbulent year in Big Dig history as issues related to water in the tunnels forced out several top state transportation officials.

The Globe reported last year that the Big Dig’s chief engineer, Helmut Ernst, wrote in a memo to his bosses that constant water leaks in the tunnels were causing safety problems and at least $150 million in damage, including corroded electrical systems and flooded air vents, and even damage to the enormous steel girders that support the O’Neill Tunnel.

In his memo, Ernst wrote that “leaks greatly contribute to the moist corrosive tunnel environment,’’ especially when combined with road salt.

But Ernst attributed the fallen light to a much larger problem: the salty ground water that seeps in through cracks and other openings in the tunnels.

However, Ernst was fired in August after saying publicly that Big Dig engineers tried to avoid putting into writing discussions of problems in the tunnels. In fact, Ernst’s team of engineers filed no reports on the light fixture collapse after it happened.

On Wednesday, DePaola acknowledged leaks as an ongoing and permanent issue.

“We continue to work on the leaks,’’ DePaola said. “I think we are slowly reducing the amount of leaks in the tunnel, but there will always be some infiltration. And we will always be dealing with sealing off leaks.’’

SOURCE: http://www.boston.com/news/local/massachusetts/articles/2012/04/05/big_dig_tunnels_need_54m_light_replacement_mass_officials_say/?page=1