Category Archives: Bridges

Cost of Corrosion Increase – Forth Road Bridge

Significant inaccuracies in the as-built drawings for the Forth Road Bridge’s cable anchorages are to dramatically increase the cost of corrosion investigations, the “New Civil Engineer” publication learned this week.

Examination of the bridge’s southern anchorages – which hold the huge suspension cables in place – is taking much longer than anticipated because they are deeper and steeper than the on the original as-built drawings.

The Forth Estuary Transport Authority (Feta) is investigating the condition of the 48 year old anchorages after a resident engineer’s report raised concerns about the possibility of corrosion in the post tensioned strands within them.

In a capital update report to the bridge authority, Forth Road Bridge chief engineer and bridgemaster Barry Colford says the cost of the inspection is likely to be “significantly higher than the original estimate” of £3.5M.

“It’s a very resource driven contract,” Colford told NCE. “As the rockhead level was higher and there more was concrete [than anticipated] the contractor has had to spend more money.”

 

The anchorages are four concrete filled tunnels – 80m deep on the south side, 57m deep on the north side – and up to 14m in diameter.

The anchorages each transfer a load of 14,000t from the main suspensions cables into the bedrock.

Each anchorage consists of 114 ducts with four post-tensioned, galvanised, 32mm diameter high tensile steel strands made up of 19 wires in each.

With the original access chamber to the bottom of all four anchorages filled in, the only way to assess the condition of the strands is to dig down and open them up, said Colford.

Contractor Graham began the anchorage investigation on the southern bank in August 2011 under a New Engineering Contract (NEC) 3 Option C target cost contract with a target cost of £3.5M.

But after investigations began, engineers discovered that the ducts were 400mm deeper and were at an angle of 33˚, not 30˚ as recorded on the as-built drawings.

“It’s a significant change to what we expected and it is very disappointing the as-built drawings of a major structure were not correct,” added Colford.

Graham will begin exposing up to nine stands on each of the southern anchorages by the end of the year. Consultant Fairhurst will assess the strength of the anchorages by the end of 2013.

Colford is in discussions with Graham about the size of the compensation event – the cost of work unforeseen at tender stage – and £220,000 has already been agreed.

The extra funds for the anchorage investigation are contributing to an overall deficit of £3.5M in Feta’s capital budget for 2012/13.

Its capital funding was cut by 58% by Transport Scotland last year.

Colford said budget shortfall would be met by using some of Feta’s £5.8M reserve, as well as delaying or cancelling “non-committed” schemes on the bridge.

He was also seeking additional funds from Transport Scotland.

SOURCE: http://www.nce.co.uk/news/structures/forth-anchor-corrosion-probe-costs-pushed-up/8635624.article?blocktitle=Exclusive-news-from-NCE-magazine&contentID=204

Tobin Bridge rates ‘fair’ in corrosion reports

State-issued inspection reports released on Friday in the wake of a corroded light fixture tumbling onto a ramp of the Maurice J. Tobin Memorial Bridge show that the 62-year-old structure is in “fair” condition with some “severe” structural deficiencies.

The structure of the bridge, which is currently undergoing a $45 million repainting and rehabilitation, was downgraded from a rating of 6, or “satisfactory”condition, in a 2009 state Department of Transportation inspection report to a 5, or “fair” condition, in its most recent 2011 report.

“We base our inspections on the overall rating of the bridge. While some elements of the structure are showing greater signs of wear … the structure as a whole is sound,” said MassDOT spokeswoman Cyndi Roy. “If the rating were to decrease to a 4 (or poor) we would then begin annual inspections of the bridge, versus the current schedule of every two years — the national standard.”

The area where the bridge deteriorated the most from 2009 and 2011 was in its girders and beams, now rated as having “severe/major deficiency.” Deteriorated and cracked concrete parts of the bridge’s substructure columns also were given the same “severe” rating in both the 2009 and 2011 reports.

“It’s not totally unacceptable to have some level of corrosion, especially given the bridge’s location right on the harbor, where the mist and salt lend to creating some corrosion,” Roy added.

The DOT released the bridge reports after holding a press conference to announce that crews overnight Thursday removed seven spotlights from the bridge after one of the lights — there are total of 18 on the bridge — broke free from a bracket under the Tobin’s upper deck and came crashing down onto an approach ramp to Route 1 in Charlestown.

SOURCE: http://www.bostonherald.com/news/regional/view/20220721tobin_bridge_rates_fair_in_reports/

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

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

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.

http://www.recordonline.com/apps/pbcs.dll/article?AID=/20120409/BIZ/120409746/-1/NEWS

Lights out for the Blatnik Bridge?

The iconic lights that outline the Blatnik Bridge linking Duluth and Superior will go dark and come down later this year during maintenance on the bridge.

Whether they return when the work is complete in 2013 is up in the air.

Corroded, in the way and “failing at an alarming rate,” the more than 200 decorative lights and their wiring have to be removed as part of a $12 million, two-year maintenance project on the bridge that’s slated to start in May, said Beth Petrowske, public affairs coordinator for the Minnesota Department of Transportation in Duluth.

Putting the lights back up and replacing the wiring is estimated to cost $1.2 million. Minnesota generally splits costs with Wisconsin on Blatnik and Bong bridge projects, but the Blatnik’s decorative lights were a project initiated and paid for on the Minnesota side from the beginning back in the 1990s.

That’s the catch in replacing them.

MnDOT is “willing to cover and can commit to our 50 percent” of the replacement cost, or $600,000, said Duluth District Engineer Mike Tardy. But now, in a time of tight budgets and many other pending road projects, MnDOT says it wants Wisconsin — or some other source — to chip in for the other half.

“I understand that the decorative lights on the Blatnik are an important feature for the area,” Tardy said. “Our challenge is that the price tag to replace them is really substantial. The funding has to come from somewhere.”

To be clear, the lights in question do not include traffic lights and navigational beacons — only the bridge’s “aesthetic” lighting.

State Sen. Roger Reinert, DFL-Duluth, has gotten involved in the issue, reaching across the bridge to Superior Mayor Bruce Hagen and, in turn, officials from the Wisconsin Department of Transportation in an attempt to find a solution.

“I was incredulous, (thinking) ‘this can’t be possible,’” Reinert said of when he first heard the lights might be going away. “In terms of Duluth landmarks, I think of the Lift Bridge, Enger Tower and the Blatnik. … The idea of it being gone is just flat-out not OK by me.”

As for WisDOT chipping in money toward the lighting, Chris Ouellette, communications manager for WisDOT’s Northwest Region, said, “We haven’t said yes, but we haven’t said no.

“Our department is in the process of drafting policy for decorative lighting and how funding for that type of project might work,” she said. That discussion is taking place in Madison, she said, and there might be more details to report this week.

Wisconsin Rep. Nick Milroy, D-South Range, said he expects the lighting to be discussed during the annual Superior Days in Madison this week. But he said tight budgets may make it a tough sell.

“I think it’s going to be very difficult,” Milroy said. “It’s something that a lot of people think is an amenity” instead of a necessity.

“When there’s not a lot of money to go around you have to prioritize what’s important,”

Reinert said the goal is for the two states to split costs. But if that doesn’t happen, he said, he and Rep. Kerry Gauthier, DFL-Duluth, have drafted a bill to require MnDOT to find the money to reinstall the lights. Both legislators said that’s an option they don’t want to use.

“We’re hoping that MnDOT will partner with WisDOT to get the money to get those lights back up,” Gauthier said.

The lights

The decorative lights on the Blatnik originated with a letter from Duluth businessman Monnie Goldfine to then-state Sen. Sam Solon in 1991, said longtime MnDOT spokesman John Bray, now retired after three decades with the agency.

“A lit-up Blatnik Bridge would be a symbol of uniting Duluth with Superior and would serve as a sign that we welcome visitors,” Goldfine wrote in another 1991 letter on the topic to city and state officials.

The letter was written as planning was under way for a massive overhaul of the Blatnik Bridge in 1993-94, when the span was completely closed to traffic for months.

The lights were installed and — after a long delay caused by water leaks into the fixtures — they officially debuted on Nov. 21, 1996.

Since that time, they’ve become a familiar sight in the Twin Ports — and they’ve been subjected to a lot of abuse from Mother Nature and passing traffic.

“The lights are exposed to the harshest environmental conditions that there can be: rain, wind, snow, salt that can cause corrosion … vibrations from heavy trucks. It’s pretty intensive maintenance,” Tardy said.

Now the fixtures have to come down to allow for sandblasting and painting of gusset plates this summer. They’ll be saved for possible reuse; the corroded conduit and wiring won’t be.

The annual expense of operating the lights is about $15,000 to $20,000 — also paid for entirely by Minnesota at present, though Tardy said that’s of less concern than splitting the more-significant restoration cost. There’s a chance operating costs could be reduced with the use of LEDs or other, newer lighting technology if the lights are reinstalled.

Tardy said he’s hoping the return of the Blatnik lights is less an “if” and more a matter of “when.”

“I’m optimistic that we’re going to be able to make this work,” Tardy said.

SOURCE: http://www.duluthnewstribune.com/event/article/id/223396/

Corrosion threat on Ohio bridge deck discovered

Grout packed into bundles of steel cables that compress the Veterans’ Glass City Skyway’s concrete deck sections together may contain elevated levels of salts that would cause those cables to corrode prematurely, the grout’s manufacturer has warned the Ohio Department of Transportation.

The I-280 bridge over the Maumee River, which opened five years ago, is one of several dozen projects across the United States that used grout made at a Marion, Ohio, plant owned by Sika Corp. U.S. in which excessive chloride compounds, traced to cement the plant bought from an unnamed supplier, have been discovered.

Also potentially affected is the Perry Street bridge in Napoleon, which carries State Rt. 108 over the Maumee and was replaced in 2005, the U.S. 33 bridge over the Ohio River between Pomeroy, Ohio, and Mason, W.Va., and as many as eight other smaller bridges in Ohio. Mike Gramza, the planning and engineering administrator at the transportation department’s district office in Bowling Green, said about 30 projects were affected overall.

Mr. Gramza and a Sika spokesman both said last week they are not yet sure that the particular batches of grout used in the Toledo or Napoleon project contained the elevated chlorides. A company alert identified all grout produced in Marion during an unspecified time that ended in March, 2010, when production there stopped.

In the worst case, they said, chloride presence would not create an imminent — or even short-term — safety hazard on the $273 million bridge built between 2002 and 2007.

But there is the possibility, they said, that as the bridge ages, chloride in the grout could cause the cables — known formally as “post-tensioning tendons” — to corrode and fail sooner than they otherwise would.

Samples will be taken within a few months from the Skyway, Mr. Gramza said, for testing “to see if there is a problem or not.” “It’s not an immediate issue,” he said, “But it could impact the life of the structure.”

More than 3 million pounds of grout from five sources was used on the I-280 bridge to seal ducts through which the post-tensioning strands pass. Those cables, which are distinct from the stay cables that support the bridge deck vertically, compress the bridge’s precast concrete segments against each other and also maintain transverse tension to reinforce the structure.

Grout is a mixture of water, cement, and sand that hardens once mixed. Its purpose in post-tensioning tendons is to protect the steel cables from moisture, road salt, and anything else that would cause them to rust.

Mr. Gramza said the transportation department’s specifications for project materials included an 0.08 percent limit on chlorides in the grout, a normal industry standard. But the suspect grout from Marion, he said, had chloride concentrations as high as 0.5 percent.

Chlorides — the most common of which is sodium chloride, otherwise known as table salt — accelerate the corrosive action of water and oxygen on metals such as steel.

So as long as the grout keeps air or water from reaching the post-tensioning tendons, chlorides’ presence in the grout causes no damage.

But over time, it is likely that tiny cracks will develop in the grout. Any air or water that seeps into it through the post-tensioning tendons’ outer ductwork might eventually reach the cables themselves, delivering the grout’s chlorides — plus any salt already in the water from ice control on the bridge — to the cables and initiating the corrosive chemical reaction that creates rust.

Mr. Gramza said that although grout delivered to the project was tested for strength, it was not tested for chemical composition. The transportation department learned of the problem in “late October or early November,” when it was notified by Sika, he said.

Diana Pisciotta, the Sika Corp. spokesman, agreed that grout is not routinely tested for chloride concentration.

She would not elaborate on how the problem came to Sika’s attention, disclose the source of the cement used at the Marion plant, nor comment on any theories Sika may have about how that cement came to be high in chlorides. But she said the company had been forthright in notifying the grout’s users once it identified where material made in Marion had gone before production halted in 2010.

“We at Sika are not happy that this has happened. We have tried to be proactive in reaching out to people. This really is a situation where you want to be aware,” Ms. Pisciotta said. An advisory describing the matter on a Sika company Web site, dated Dec. 6, said the company had, “over the past several months,” been “working aggressively to address reports” of excessive chlorides in SikaGrout 300 PT product made in Marion.

“There is a concern that, depending on the level of elevated chlorides in the grout in installed locations, the risk of corrosion in the tendon strands could increase,” the advisory said. “While this issue could affect the long-term service life of certain infrastructure projects [roads, bridges, etc.] where the impacted grout was used, Sika is unaware of any damage to structures to date arising from this elevated chloride issue.”

In November, 2010, Sika began “an enhanced quality-control testing regime” that includes chloride analysis for SikaGrout 300 PT made at other plants.

With one exception, listed by the company, all of the Marion-produced grout had lot numbers ending with the letter “M” on bags of the material.

Mr. Gramza said detailed records were kept showing the sources of grout used on various areas of the I-280 bridge, so sampling will be limited to areas where Sika’s Marion-made grout was used. Samples will be tested at a transportation department laboratory, a Sika lab, and a third-party location, he said.

“If there is a problem, we will have to investigate it, and evaluate the potential impact on traffic,” he said. The transportation department will consider Sika liable for the cost of any corrective measures, Mr. Gramza said.

Asked Sika’s position on its liability exposure, Ms. Pisciotta responded: “Our intention is to collaborate with them [ODOT] as they review this issue. We will continue the conversation with them as to what the appropriate next steps are.”

The grout problem is at least the fourth significant materials problem with the Skyway.

In 2004, about 184 cubic yards of concrete was removed from the bridge’s central pylon after sample testing determined a particular batch was weaker than required. Later in the project, officials discovered cracks in the plastic coatings on the bridge’s stay cables and ordered them replaced at the supplier’s expense.

And in 2008, a year after the bridge opened to traffic, inspectors discovered that epoxy glue holding the stay cables’ stainless-steel sheaths together was not holding up and the sheaths were slipping. The sheaths were welded together to remedy that problem.

The bridge also has had sporadic problems with ice forming on its pylon and stays during winter storms, then falling off in sheets onto the roadway when the weather warms, but so far this winter, such ice has not been an issue.

SOURCE: http://www.toledoblade.com/local/2012/02/06/Corrosion-threat-on-Skyway-bridge-deck-discovered.html

Montpelier pedestrian bridge closed over safety concerns

Josleyn Willscheck and Anthony Iarrapino hit a dead end on their afternoon walk through downtown Montpelier, VT.

“It’s not the end of the world, but it’s just not the perfect walk during the work day,” Willscheck said.

The city closed the pedestrian bridge that connects Route 2 with State Street over the Winooski River, saying it is no longer safe for people to walk on.

“I wouldn’t say the bridge would collapse, but portions possibly,” said Todd Law, the director of Montpelier Public Works.

The bridge is so corroded underneath that holes are popping through. The bridge was built in 1998 at a cost of a quarter of a million dollars. It was expected to last 30 to 40 years. Now, it needs a major makeover.

“The bridge is made of a weathering steel, so it’s supposed to form a rust barrier around the members that protect it from further corrosion. It didn’t seem to protect it.” Law said.

Now the city is trying to find out why the bridge did not hold up.

“One is salt use. The salt adhered to the members and corroded them. Second, we just heard– it’s a fairly new concept to our heads– that there is leaching from the pressure-treated lumber,” Law said.

Law says the city hopes to know in a week or two what it will take to make the bridge usable again. But it’s not expected to be cheap. The tab could exceed $100,000. The city noticed the corrosion several years ago and has set aside $97,000. But officials just realized the severity of the problem.

“I would like to get it done as soon as possible, if that means winter construction,” Law said.

“It’s nice to have a way across that is dedicated solely to bike and foot traffic and not motor vehicles,” Iarrapino said.

The city says the contractor is not at fault.

The foot bridge is part of the city’s bike path.

SOURCE: http://www.wcax.com/story/16465763/montpelier-pedestrian-bridge-closed-over-safety-concerns