Île aux Tourtes bridge backgrounder

NOTE: The following story first appeared in the Hudson/St. Lazare Gazette in July 2007. It was dismissed as scaremongering by the Ministére des Transports and the anglo media, including the Montreal Gazette. Since then, engineering reports by several major consulting engineering firms for the MTQ have confirmed what the Hudson weekly was first to report — the bridge is in failing health. Scheduled for replacement by 2020, the cost of keeping the Ile aux Tourtes span open is accelerating. According to the MTQ’s own figures, it will cost $65 million to keep the bridge open until then — $45M prior to 2015-16 and another $20 million by the time a replacement opens. Estimated cost of replacement: $750M. 

By Matthew Brett
Standing under the eastern side of the Ile aux Tourtes Bridge, one feels and hears the constant thudding overhead from the big rigs roaring to their destinations. The thudding has taken its toll on the bridge as the first pier to reach the water, pier 24, is almost entirely marked off with spray paint for repairs. Exposed steel bleeds rust down the pier, and a sliver of light beams through a crack where cement has spalled away.
The Hudson/St. Lazare Gazette camera snapped a series of photographs of the bridge from the shore and by boat, which provide graphic detail of what is happening to the underbelly of the 1.8-kilometre span between Montreal Island and the mainland.
The six-lane Highway 40 bridge carries an estimated 75,000 vehicles a day.
Upon examination of the photographs, bridge engineer Hellen Christodoulou said “repairs are clearly warrented.”
Christodoulou, who was involved in a post-examination of the de la Concorde overpass collapse which claimed five lives on September 30, 2005, said “the bridge design capacity remains inadequate to sustain current loading. There should be stringent requirements and monitoring of traffic loads and speeds.”
Kaare Olsen, who was Atlas Construction’s VP and Chief Engineer when construction began in 1963, was in complete agreement with Christodoulou when he saw the photographs. (Olsen, left with fellow Hudson engineer Brian White during the Gazette’s 2007 inspection tour,  passed away on March 23, 2014 at the age of 91.)

“When we built that bridge it wasn’t meant to take the load its taking today,” he said. “They didn’t visualize the capacity that’s going now.”
The Ile aux Tourtes was one of the first pre-stressed concrete bridges built in Quebec, Olsen explained. Like an elastic, it was designed to flex under load.
Lack of maintenance, Quebec’s harsh climate and an ill-advised bridge-widening project to add a breakdown lane on both sides have contributed to the deterioration of the bridge Olsen built. Spalling, leaching and cracking are now widespread after 42 years of service. Already, the bridge has exceeded its 35-year lifespan.
“Geez, look at that,” Olsen said as he looked at a section of exposed and rusting steel. “That’s all from weathering, it’s not from any stresses.”
The weathering is exacerbated by what Olsen regards to be a poorly designed drainage system. Gaps in the concrete barriers designed to drain the surface water were placed directly above the piers, allowing water and salt runoff to erode the beams and piers.
Olsen noted the original prestressed bridge design was not taken into account when the MTQ replaced the original lightweight retaining rails with a solid concrete parapet, prompted by the number of vehicles tumbling into the Outaouais after losing control. The bridge flexes but the barriers do not.
Olsen’s comment upon seeing the deterioration of the heavily modified structure: “I didn’t build that bridge.”

(Since Matt’s original story ran, a 2011 inspection by the consulting engineering firm Genivar discovered the added breakdown lanes cantilevered onto the original outside beams have had the effect of prying them apart, exposing the original structure to even greater weathering.)
Christodoulou’s summary notes work was done on the bridge in order to increase its capacity by transforming  sections of the bridge’s initial girders into box girders —a reasonable repair, but the workmanship was substandard. She also said the box girders were only a temporary solution.
Several of the cables used to construct the box girders are rusted, “indicative of the fact that they were either not galvanized, or insufficiently galvanized,” she said.
Several sections of the bridge also reveal cracked and delaminated surfaces. “there is no doubt that the work done was a patch-up job,” Christodoulou said. She said the delaminated concrete may be the result of poor quality or fast-hardening concrete.

(Since Matt’s story was published, there has been growing concern worldwide about the catastrophic failure of structures built with calcium aluminate concrete. Originally preferred because they set, or achieved most of their final strength more quickly, these aluminate cements (ciment fondu) were widely used during the building boom in the ‘60s, ‘70s and ‘80s, nowhere more so than here in Quebec. The Europeans were the first to note the correlation between aluminate concrete and accelerated aging in dams, bridges and buildings. According to the late Brian White, most of the cost of Quebec’s deteriorating infrastructure could well be due to the widespread use of ciment fondu. White believed the failure of Hydro Quebec’s transmission network during the 1998 ice storm should be blamed on the use of ciment fondu in insulators.)

NOTE: This June 15, 2007 summary by consulting engineer Hellen Christodoulou followed a visual inspection of the Ile aux Tourtes bridge by a team which included the late Kaare Olsen, under whose supervision the bridge was built.

1) The bridge was initially a girder bridge. From the photos it is evident that work was done to deepen the girders, in order to increase the bridge capacity.
2) In order to achieve this, the individual girders were transformed into box girders, except at the end girders.
3) The photos illustrate that this transformation was done by the installation of bottom plates and vertical bars, as a means to strap the existing while lowering the bottom to increase capacity. The lowering was achieved by pouring a concrete layer to connect the girders.
4) Once the above was completed the plates and cables were left in place. It is evident from the photos that several of these cables are rusted, indicative of the fact that they were either not galvanized, or insufficiently galvanized.
5) As for the cracked and delaminated surfaces seen in the photos, there is no doubt that the work done was a patch-up job, the reinforcing used has rusted (not galvanized), the concrete has delaminated, possibly resulting from the use of poor quality or fast-hardening concrete. Repairs are clearly warranted.
6) As for the horizontal post tension cables, there lies an even more serious problem. These cables have been placed at the end girders. The photos clearly show that one of these cables has snapped off. Why is this serious? These types of cables are installed to increase the capacity at the ends and reduce flexure. The fact that they have snapped out of place implies that the bridge capacity has weakened and that section is overstressed. This situation can be quite volatile and more serious problems may occur.
7) As for the substructure (piers), it seems they have been marked-off for repairs, yet no work has been done. The spalled and delaminated surfaces as well as the rusted reinforcing bars, require immediate review and repairs.

Christodoulou’s conclusion: The concept of transforming the existing girders into box girders and deepening the sections, is reasonable, however a) the workmanship seems substandard and b) this solution is not a permanent one, since this modification may only partially increase the bridge capacity. The fact that post-tension cables were required, is proof enough that the capacity is insufficient for current loading requirements. The bridge design capacity remains inadequate to sustain current loading. There should be stringent requirements and monitoring of traffic loads and speeds.

 

 

 

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