Tag Archives: Concrete

$100m corrosion & cathodic protection project for Sydney’s tallest office building

WHEN it was finished in 1978, the 67-storey MLC Centre in Martin Place was not only Australia’s tallest office building, but also the biggest reinforced concrete structure in the world.

Thirty-three years later, the Harry Seidler-designed structure is showing its age. Its concrete facade is breaking up and the owners have agreed to spend $100 million repairing it in an operation that will go 24 hours a day, seven days a week for much of the next four years.

Documents filed by the owners with the Central Sydney Planning Committee show what a massive repair job it will be to stabilize the remaining solid parts of the modernist facade and repair those that are not.

It will take 10 months just to finish preliminary works.

Then workers on 12-hour shifts will blast away damaged concrete with dry ice and grit, and use small jackhammers and angle grinders to prepare the surfaces for filling and patching.

They will also drill thousands of 100 millimeter-deep holes into which anodes will be inserted, which should help preserve the facade panels for the next 40 years.

This main stage of the process will last more than two years. To minimize disruption to tenants, the owners have decided the noisiest work will begin at 7pm and go all night, a decision that has angered neighboring residents who have objected to the plans.

The owners, GPT Group and QIC Real Estate, will import insulated French working platforms designed to fit the shape of the building, which they say will reduce the noise of the jackhammers and other equipment.

The owners blame the deteriorating facade on ”the manner in which pre-cast panels were originally manufactured”.

SOURCE: http://www.smh.com.au/nsw/four-years-and-100m-for-city-tower-repair-job-20111106-1n225.html#ixzz1d2Jdl3D7

Corrosion – Fatal Impact on Concrete Wall Flaw

A deficiency in the concrete wall construction of the basin at the Gatlinburg Wastewater Treatment Plant led to the basin wall collapsing, killing two employees in April, a report from the state issued Thursday says.

“Walls were cast in a manner that produced a cold joint between the cast wall which fell” and three interior intersecting walls, according to the report from the Tennessee Occupational Safety and Health Administration (TOSHA).

TOSHA announced in early October that it found no safety violations at the plant, and this week released a five-page report that was the basis for that finding. When TOSHA announced in early October there were no safety violations, it didn’t give a probable cause of the basin wall collapse.

The new report does. What its inspectors call a “cold smooth joint” led to leakage of acidic waste across the joint, and “as a result, corroded the rebar splice couplers over a number of years.”

The couplers were not believed to have failed at one time, but gradually over the life of the basin, the report said.

When the findings of no safety violations were announced earlier this month, Veolia spokeswoman Karole Colangelo said, “Although the findings from TOSHA reinforce our emphasis on employee safety, it does not dismiss the fact that two Veolia Water employees perished in this tragic accident, and company employees continue to mourn their deaths.”

“It was assumed the two operators were making adjustments to the effluent flow inside the equalization basin,” the report says. While the men were working, the wall collapsed and fell on the building in which they were working.

The collapse sent about 850,000 gallons of untreated wastewater into the Little Pigeon River and forced the city to pump more untreated water into the river until it could come up with a temporary solution a few days later.

According to the workers’ last journal entry at 5:30 a.m. that day, the basin contained 1.3 million gallons of water and was 85 percent full. The water level was recorded at 25.5 feet. The report says interviews with operators and plant officials show the average water level was 4-8 feet.

The plant is owned by the city but managed by Veolia Water North America Operating Services LLC. Veolia officials told the state inspectors that both Crowder Construction Co., that built the plant and Flynt Engineering Co., that designed it are out of business. The basin was finished in 1996.

TOSHA learned that after the basin was finished in 1996 the north wall had cracks and a lateral displacement/bowing of the wall and walkway. Veolia told the state that buttresses were installed that “corrected” the problems with the wall and walkway.

TOSHA noted that the flow control building where the workers were is still not accessible, but the state says “we have no probable reason to think that access to this area would reveal any additional information that would result in citation being issued to Veolia.”

The report says the contractor used “splicing couplers” instead of dowels, as required in the original drawings, noting that while that was a “deviation” from the design, it was probably not the cause of the collapse. The report did say that “formation of a cold joint resulted in accelerated corrosion of the couplers.”

TOSHA reviewed the original design of the basin and found the design of walls “adequate.”

SOURCE: http://themountainpress.com/view/full_story/16198627/article–Report–Wall-flaw-caused-accident-?instance=main_article_top_stories

Corrosion problems identified in Melbourne’s City Loop

Serious structural problems in Melbourne’s City Loop – including cracking tunnel walls, concrete corrosion  – have been ignored by successive state governments and train operators despite repeated warnings.

A 2001 report, also obtained by The Age, revealed the loop was suffering from long-term structural corrosion caused by possible contamination of the original concrete mix.

Damage to concrete plinths was leading to ”heavy corrosion” of steel reinforcements, potentially undermining the tracks. At worst, a derailment ”must be considered possible”, said the report, commissioned by infrastructure contractor Thiess Infraco.

Transport Safety Victoria has also expressed concern about the 30-year-old loop, after receiving a letter of complaint from the train drivers’ union. The letter, addressed to Metro and copied to the Coroner, said drivers had ”grave concerns” about the operator’s failure to address evacuation procedures.

The drivers say they are not trained for emergencies in the loop. Their occupational health and safety representatives yesterday issued Metro with a formal warning that will trigger a WorkSafe investigation.

The Age investigation into City Loop safety has revealed:

  • Drawings of fire-protected areas of underground stations have been lost.
  • A recent CSIRO study of the smoke extraction fans found some were performing to a capacity of only 25 per cent.
  • Train drivers have noticed record levels of water seeping through the walls, along the tracks and on the emergency walkways. Metro says, however, that the water is not a safety risk.
  • Train drivers have been asking Metro for six months for an after-hours train to inspect the tunnels. Metro has refused.

Metro, which took over the rail system from Connex in 2009, could not confirm yesterday whether these problems had been tackled.

But it said structural problems with the concrete would be addressed in a rehabilitation program starting next April.

Metro spokeswoman Geraldine Mitchell said 6125 sleepers would also be replaced by November as part of general maintenance.

She said two independent reports – one commissioned by government and one by Metro – had concluded that safety standards had been met.

In a statement to The Age, the Department of Transport said the loop was performing ”optimally” and ”a range of maintenance, repair and mitigation” measures had been conducted since the 2001 report.

The loop had been tested – including state-of-the-art smoke testing – and emergency exercises completed. ”The department believes the potential for a train derailment in the rail loop is extremely low,” it said.

”The emergency walkways located in the loop are subject to ongoing maintenance and repair.” Representatives from the government’s insurance authority had recently inspected the walkways and found them in an ”adequate condition”.

Transport Minister Terry Mulder did not answer when asked by The Age whether he knew about the reports. But he said he expected the department and Metro to hold safety as paramount. ”As minister, my priority is for the safety and security of passengers,” he said.

SOURCE: http://www.theage.com.au/victoria/city-loop-safety-fears-20110921-1klbd.html#ixzz1YjH0c7qH

12 Montreal structures considered critical due to corrosion

Montreal Mayor Gerald Tremblay said on Wednesday that 12 bridges, tunnels and overpasses in the city identified by engineers as being in critical condition.

“We have the reports from our engineers that these structures are safe,” Tremblay told reporters at city hall, where technical details on 35 structures were made public.

“From the moment one of our engineers or technicians informs (us) they are not safe, we will close the structure or limit access to it either by (reducing the number of) lanes or limiting the load.

“Just because it is critical doesn’t mean it isn’t safe.”

The mayor also said his administration is raising the annual average amount needed for repairs to $50 million from $30 million because of the advancing age of the 586 structures in the city of Montreal’s network. The request for more funds will be made in a new three-year infrastructure plan to be unveiled Thursday, Tremblay said.

On Wednesday, the city of Montreal made public inspection reports for 35 infrastructures on its territory. Of the 12 listed in “critical” condition, two are closed to the public, and one has undergone major repairs since the information was collected late last year.

The 12 in “critical” condition are:

  • Henri Bourassa Blvd. E./Pie IX Blvd. overpass
  • The former Wellington St. Tunnel under the Lachine Canal
  • Henri Bourassa Blvd. E./Metropolitan Blvd. E overpass
  • Rockland Ave./Bates Rd. overpass
  • Beaudry Tunnel, north side of Notre Dame St. E., near the Port of Montreal (private roadway)
  • Jean Talon St. W. overpass (west of Wilderton Ave.)
  • Jolicoeur St. bridge over Montreal Aqueduct
  • CN Rail bridge crossing l’Acadie Blvd., north of de Louvain St.
  • Park Ave. overpass/Highway 40 and service roads
  • Henri Bourassa Blvd. E./Sherbrooke St. E. overpass
  • Upper Lachine Rd./St. Jacques St. overpass
  • Snow ramp at St. Michel Quarry (no public access)

The reports detail the sites’ deterioration:

  • The Henri Bourassa Blvd. E./Pie IX Blvd. site has support walls that are severely cracked. Exposed reinforcement bars have also been badly corroded.
  • Pillars have a series of cracks in them, with eroded concrete.
  • The Wellington Tunnel, which has been out of service since the roadway was rebuilt as an overpass, suffers severe corrosion on 66 per cent of the structure’s support system.
  • The Henri Bourassa Blvd. E./Metropolitan Blvd. site has corroded beams and severe damage to the structure’s decking, with a risk of falling concrete.
  • The Rockland Ave. overpass’s support structure has lost about 10 per cent of its load-bearing capacity. Concrete is eroding and exposing reinforcement bars to rust and corrosion.
  • The Beaudry Tunnel has severe water damage.
  • Jean Talon St. W. overpass has severe corrosion to its support structure.
  • The Jolicoeur St. Bridge has cracks covering 30 per cent of the supporting walls’ surface.
  • The CN Rail bridge crossing l’Acadie Blvd. has cracks covering 100 per cent of its supporting pillars. About 15 per cent of the supporting walls’ surface is severely damaged.
  • Park Ave. overpass/Highway 40 and service roads: Expansion joints have been paved over. About 40 per cent of the joints’ surface is defective.
  • On the Henri Bourassa Blvd. E./Sherbrooke St. E. overpass, about 80 per cent of the concrete on the eastern wall is severely chipped.
  • At the Upper Lachine Rd./St. Jacques St. overpass, 40 per cent of the support walls’ concrete is severely chipped, exposing reinforcement bars to corrosion.
  • At the snow-dumping ramp at the St. Michel Quarry, 90 per cent of the support wall is covered in cracks, chips and ruptures.

No immediate repairs are planned for the Wellington Tunnel and the Beaudry Tunnel, as both sites are off-limits to the public.

An additional site, the St. Jean Baptiste Blvd. overpass at Highway 40/Metropolitan Blvd. E., was missing waterproofing membrane along its expansion joints, causing moisture to seep in. Concrete was also badly damaged along the joints. Repairs have begun at this site.

In Montreal’s disclosure, the city made public, for each of 35 structures, one-or twopage “inspection summary sheets” on which engineers have rated the deterioration of various elements. For each of the 35, photos of trouble spots were also provided.

Richard Bergeron, of the opposition Projet Montréal party, accused the city of holding back more detailed “engineers’ reports” for its structures.

But city spokesperson Philippe Sabourin denied that. He said the documents made public Wednesday are the complete inspection reports. “We don’t have any other reports,” Sabourin said.

By month’s end, the city is to publish on its website more information about the 520 other structures under its control. For those, Montreal will release the same type of “inspection summary sheets” but will not include photos, Sabourin said.

Tremblay said the city will henceforth provide annual updates on the state of every one of its structures via its website.

This week, Quebec Transport Minister Pierre Moreau pledged to make public inspection reports for all 10,000 structures under his control.

He did not provide a timeline.

SOURCE: http://www.montrealgazette.com/structures+considered+critical/5401145/story.html#ixzz1Y1MUaLdE

Florida’s St. Augustine Beach Pier Corroding

According to St. Johns County officials, the stretch of coastline from south Georgia to Fort Lauderdale is the most corrosive in the nation.

Evidence of the corrosion can be seen on the St. Augustine Beach pier, one that’s 25 years old and nearing the end of its lifespan.

Janice Vose, who spent her time under the pier Tuesday, said she had the best seat on the beach.

“It’s shady. There’s a breeze,” Vose said.

But what she didn’t know was she could have been in danger.

A few months ago, during a routine inspection, an engineering firm found the pier has problems, most visibly the corrosion on the pilings holding it up and cracks in the concrete.

Engineers advised the county to take action, so county officials installed netting under the pier to catch any falling debris and also posted warning and danger signs to be extra safe.

“A small chance, a remote chance that some concrete could spall off of the concrete structure portion due to the rebar rusting and cause a problem, so we put up the signs as a precautionary measure,” said Mike Rubin, St. Johns County director of construction.

Most people walk right under the pier without noticing the signs, but Rubin said it would take a big storm to knock down such a sturdy structure.

“If a failure were to come, it would be when the pier would be under maximum stress during a hurricane event or a big storm or big wave action, and there’d be no one on the pier at that time anyway,” Rubin said.

The 650-foot-long pier is supported by pilings up to 36 inches in diameter.

“Those metal pilings that you’re seeing are actually filled with concrete,” Rubin said. “There’s rebar in the top 10 feet of them, and while the concrete doesn’t really provide a lot of lateral structural strength, the real strength is in the pilings themselves.”

The big question is exactly how much the pilings have decayed over time. Until that’s answered, Vose said she’s staying put.

“I’m in paradise. I feel so grateful,” she said.

The county plans to have the engineering firm take a closer look to evaluate the extent of the damage, and then the board will decide what to do. A new pier is a possibility in St. Augustine’s future, but it would probably be about five years before one could be built.

SOURCE: http://www.news4jax.com/news/28884204/detail.html

Plymouth Avenue bridge closed until next year

There’s good news and bad news for traffic users of the Plymouth Avenue Bridge. The good news is that city officials appear to have found the money needed to repair the bridge. The bad news is that it will probably be a year or more before the bridge is open to motor vehicle traffic.

Minneapolis City Engineer and Public Works Director Steven Kotke said most of the money is coming from the State of Minnesota. “We were successful in obtaining two different pots of money. One was kind of an emergency fund that the state had, and then the governor actually put in the state bonding bill $4 million for the Plymouth Bridge, and that gave us a grand total of right around $6 million, which is about what we think we need to fix the bridge.”

He said, however, that the various parts of the repair work need to be done in a certain order and in very close succession, and there’s not enough time to do it all this year. So they won’t be able to start the work until next year.

“The work needs to be sequenced in a continuous manner, so that would not allow us to do the work this fall and then stop for the winter and the start again,” he said. “We intend to get the project all bid out and start first thing in the spring. We’re anticipating it will be about four months worth of work, so that would put us probably near the end of August of 2012 to have the bridge completed and opened back up.

“So the good news is we were able to give everybody the green light to keep moving forward. It would have been nice if we could have started right away, but given the manner of the work that needs to be done, it would prevent that from happening,” he said.

“So we are continuing to finish the final design, and then it has to go through a state review process to make sure everything is right.”

The bridge crosses the Mississippi River and connects Eighth Avenue NE and Plymouth Avenue N. Motorists can cross the river using the Broadway Bridge six blocks to the north.

City engineers closed the Plymouth Avenue Bridge Oct. 22 after finding corrosion in its support system during a routine annual inspection. It was built in the 1980s and was the first of its kind—called post-tension segmental box girder—in Minnesota. City officials brought a consulting firm that specializes in this bridge design, to inspect the bridge and recommend repairs.

They found serious corrosion in at least five of the post-tension tendons in the bridge’s center span. These tendons, Kotke said earlier, are similar to the cables that support suspension bridges, and are designed to keep the bridge’s concrete parts pushing inward when a load is placed on the bridge surface. The concrete, he said, is strongest when it’s in this “compression mode.”

An initial report, issued in late December, recommended four major repairs:

  • Reconfigure the bridge’s drainage system to direct water away from the bridge’s box girders
  • Replace five of the bridge’s corroded support tendons
  • Add more tendons to improve the bridge’s flexing capability
  • Seal the bridge’s wearing surface with a penetrant sealer, or replace the wearing surface.

The bridge is currently open to pedestrians and bicyclists; bicyclists are asked to walk their bikes while on the bridge.

SOURCE: http://www.tcdailyplanet.net/news/2011/08/14/plymouth-avennue-bridge-closed-until-next-year

Iowa bridges third-worst in the nation

At first glance, the two-lane bridge over Wapsinonoc Creek seems up-to-date. But a closer inspection reveals rusted bolts, graffiti, and crooked beams. More than 4,000 cars travel across it each day, and it has not been renovated since 1956.

The bridge, located in Muscatine County, is one of 5,000 bridges in Iowa classified as structurally deficient, giving Iowa the third-worst bridge conditions in the nation, according to a recently released report.

Although the report said bridges all over America are in a sad state of repair and getting worse, Iowa’s bridge problem stands out by several measures.

More than 40 percent of Iowa’s spans are more than 50 years old, which is the normal design life span of a bridge.

Nearly 22 percent — more than one in every five bridges — are structurally deficient, and that is almost double the national average. For comparison, the states doing the best job of keeping their bridges safe are Nevada, Florida, Texas, Arizona, and Utah, where deficient bridges range from 2.2 percent to 4.5.

The report “The Fix We’re in For: The State of Our Nation’s Bridges,” was released in late March by Transportation for America, a group mainly concerned with maintaining the nation’s current infrastructure, according to spokesman David Goldberg.

The report’s findings put Pennsylvania and Oklahoma as the only states with a higher percentage of structurally deficient bridges than Iowa.

“The nation’s bridges are aging and traffic demands are increasing, even as state and local revenues are shrinking,” the report said. And the problem is likely to keep getting worse, because state-level needs have nearly doubled since 2006.

The report called on the U.S. Congress “to ensure that [federal] funds sent to states for bridge repair are used only for that purpose.”

And it warned states that deferring maintenance of bridges is not only a safety risk but a false savings. “Deferring maintenance of bridges and highways can cost three times as much as preventive repairs,” it said.

On the list of the worst 100 counties, Iowa holds 17 of the spots, more than any other state, with Adams County being the 10th-worst in the country. Almost 47 percent of Adams County’s bridges are structurally deficient. Winnebago, Davis, Lucas, and Plymouth Counties not far behind. The counties with the safest bridges are Clinton and Jackson.

“We try, as money permits, to keep improving them,” said Eldon Rike, the bridge engineer for Adams County.

Out of the 24,722 bridges that motorists use in Iowa, 5,371 of them are considered structurally deficient, according to the study, meaning engineers have rated one of the three bridge components at a 4 or less on a scale from 0 to 9, 9 being the best condition. These numbers then contribute to the overall condition of the bridge, which is on a scale from 0 to 100. This number is called the “sufficiency rating.”

“We’ve known about this for a while,” said Norm McDonald, the director of the Office of Bridges and Structures for the Iowa Department of Transportation. “We use the funding and do the best we can.”

SOURCE: http://www.dailyiowan.com/2011/06/30/Metro/23950.html

Spring River bridge to be replaced due to corrosion

If the deck on the Missouri Highway 96 bridge over the Spring River near Kellogg Lake Park were rated any worse, the bridge would have to be closed.

According to Jerry Davis, a transportation project manager for the Missouri Department of Transportation, the deck of the Highway 96 bridge that crosses Spring River received a rating of three on the department’s nine-point scale for rating bridge decks, superstructure and sub structure, due to a significant corrosion problem.

“A new bridge would be a nine and if the rating falls to two it needs to be closed,” Davis said. “The deck is saturated with salt water from snow removal and it has eaten away at the steel in the deck.”

That’s why MoDOT plans to replace the bridge in the summer of 2012. The project will likely start in May or early June and last between 90 and 120 days. A detour has yet to be determined, Davis said.

Most cars and light trucks can get around the construction by using North Garrison Street and County Route V in Kendricktown, but the nine-ton weight limit on the three bridges on North Garrison Street means tractor trailers will have to take a different route.

Davis said the official detour will be established to carry all traffic around the construction.

Davis said the deck has been patched many times but that doesn’t fix the underlying problem.

Davis and Mike Hobbs, a transportation project designer with MoDOT, set up a map of the area for the public to examine at Tuesday’s meeting, but attendance was light.

City Administrator Tom Short, Chamber President Sabrina Drackert and City Council Member Ed Hardesty came early to learn the specifics of the project and offer comments.

Short showed Hobbs and Davis the Visioning Plan created by the students from Drury University for enhancements to the entrances to Carthage, especially on Missouri 96 where many tourists traveling the historic Route 66 enter and leave town.

The plans call for sweeping structures to enhance the look of the bridges coming into Carthage.

Davis said the department would look at those plans, but the department currently plans to replace that bridge with something similar.

“I don’t see where we can do much about the esthetics,” Davis said. “We’re trying to stretch every dollar we have and to do something like that would add too much cost to the bridge.”

He said the new bridge would look similar to the one that’s there now except it would have concrete girders instead of steel and it would be slightly longer — 505 feet versus the current 490 feet.

Davis said the state plans to replace another bridge on County Route O over Spring River south of Alba at the same time it is replacing the Carthage bridge.

People who could not attend these meetings may go on the Internet to http://www.modot.org/southwest/publicmeetings.htm to express opinions or voice concerns.

SOURCE: http://www.carthagepress.com/news/county/x217706721/Spring-River-bridge-to-be-replaced

Aging U.S. 2 trestle gets needed corrosion repairs

With thousands of vehicle trips daily, U.S. 2 gets needed repairs

EVERETT (WA) — Concrete is falling off in chunks, rebar is rusting and thousands of people drive over the westbound U.S. 2 trestle every day.

While the girders on the trestle’s underbelly have been slowly deteriorating for more than 20 years, state transportation officials say there’s no doubt the bridge is safe for drivers. Repairs are being made this summer and fall.

About 37,000 vehicles per day use the trestle in one direction or the other.

“There’s no problem with people driving on the structure,” said Chad Brown, project engineer for the trestle repair. “The structure is safe.”

Workers are restoring the exposed rebar, replacing the concrete on the girders and sealing them to keep them waterproof. The repairs are expected to preserve the girders on the now 43-year-old span until 2026 or longer. The $8 million project began earlier this month and is expected to be finished in the early fall.

The roadway on the trestle is built atop girders made of concrete and rebar, running lengthwise with the roadway, sitting atop crossbeams that in turn sit on pillars. The eastbound half of the trestle was built with timber in the 1930s and rebuilt in sections in the 1990s, according to the state. The westbound side was built in 1968.

By 1987, crumbling began to show on the concrete beams on the underbelly of the westbound structure, and the bridge was declared “structurally deficient.” The term is a federal designation meaning that a bridge has a part or parts that will eventually need to be repaired, not that it is unsafe, according to the state. Washington currently has 143 bridges in this category, including seven in Snohomish County.

Under the state’s routine inspection program, bridges are examined every two years. Some with more structural issues are put on a yearly schedule, and the trestle has been inspected every year since 2003.

The section currently being repaired was done four years after the other section because of funding issues and environmental regulations involved in working over Deadwater Slough, officials said.

The current repairs are being done in the same manner as in 2007. The bridge at the far west end of the trestle, over the Snohomish River, is newer and won’t be repaired in this cycle.

Engineers are confident the moisture has not further penetrated the beams. So far, the farthest into any beam that weak concrete has been found is a couple of inches.

Traffic on the westbound trestle will be shut down for up to 65 nights through early October for the concrete and carbon-fiber mesh work. These phases have to be done when there’s no traffic on the road so vibrations won’t prevent the concrete from setting properly or keep the mesh from bonding to the concrete, engineers said.

The trestle was closed for three nights on June 9, 14 and 16 while two sections were repaired. It’s possible the work will take less than the 65 nights. The next closure is planned for July 12.

If the girders are not repaired, beams and the rebar would continue to deteriorate, and longer closures would be needed, engineers said.

Nancy Singer, a spokeswoman for the Federal Highway Administration, said federal engineers say the work being done on the trestle appears to be appropriate.

“State departments of transportation are the owners and operators of infrastructure and are in a position to select the best approach to addressing the needs of a bridge,” she said in an email.

“The U.S. Route 2 project that calls for replacing old cracking concrete, removing corrosion from the steel frame, and reinforcing the girders on the underside of the viaduct seems to be based on sound and established approaches to bridge repair and rehabilitation.”

SOURCE: http://www.heraldnet.com/article/20110627/NEWS01/706279969

Gardiner structurally sound, experts say, after chunk smashes onto road

TORONTO: City crews will be examining sections of the Gardiner Expressway after a 4.5-kilogram chunk of concrete fell onto Lake Shore Blvd. W. earlier this week, hitting a guardrail and ricocheting into the road.

The slab, about four centimetres thick and over a meter long, was sloughed off the bottom of the elevated section, its steel reinforcing bars corroded by road salt.

No cars were hit and no one was injured. Two lanes of westbound traffic just east of Bathurst St. were temporarily closed.

The incident is the fourth in recent memory, but does not mean that drivers should steer clear of Lake Shore, city staff said.

“There really shouldn’t be any concern,” said Mike Laidlaw, Toronto’s acting manager of structures and expressways.

Aside from the dangers inherent in a chunk of concrete weighing almost as much as a bowling ball falling from the sky, the expressway itself is sound, experts say.

“The stuff on the outside, most of it could fall off without affecting the structural integrity,” said R. Doug Hooton, a civil engineering professor at the University of Toronto. “(The overpass) is not in danger of falling.”

Laidlaw said the city will be conducting extra inspections around the area. Toronto is also putting out a call for proposals from engineering firms for a complete inspection within two years.

City crews inspect the Gardiner yearly — “sounding” the concrete for unstable pieces and removing them with a hammer — and conduct visual inspections at least every six months.

“If they do see any areas of concern they’ll look after it immediately,” said Laidlaw.

In January 2007, a piece of concrete about the size of a basketball fell onto Lake Shore near York St. and narrowly missed hitting a car. A small piece fell near Spadina Ave. in February 1999 and near York St. in January 1997.

“It is a concern for anybody underneath of it,” said Laidlaw.

Hooton said the Gardiner was designed before Ontario began salting roads in the winter, so it wasn’t constructed to withstand the salt that seeps through the roadway and into the steel reinforcing bar.

The salt rusts the rebar which then expands, cracking the concrete and pushing the outer layer off. Repair work was done years ago to the road’s drainage system to prevent salt from seeping into the concrete.

“It’s not happening as much as it would have if they hadn’t done those repairs,” said Hooton.

Police said no one reported any damage to a vehicle and there were no injures.

By 3 p.m. Monday, city crews had cleared debris off the road and unblocked all westbound lanes on Lake Shore Blvd.

The incident called to mind a horrific accident in Quebec five years ago. Five people were killed when a 40-year-old Laval overpass fell onto a highway on Sept. 30, 2006, crushing several vehicles.

A year later, a commission report into the accident blamed shoddy workmanship, insufficient oversight and deficient maintenance.

SOURCE: http://www.thestar.com/news/transportation/article/1011934–gardiner-structurally-sound-experts-say-after-chunk-smashes-onto-road?bn=1