There’s a troubled bridge over Saugeen waters.
While the main structure of the bridge is not in jeopardy, according to Wellington North Public Works Manager Gary Williamson, ignoring the problem may result in the closure of the east-west artery of the bridge this winter.
Mayor Mike Broomhead said there was a small problem with the bridge that a report from engineering firm BM?Ross detailed.
Williamson said, “You know you’ve been around too long when this is the second time we’ve had to fix the deck of this bridge.”
Similar work was done in 1988.
Alluding to the later report, Williamson said while this may not be a problem with the bridge structure, it could turn into a major project. “It is a major issue which needs to be addressed immediately.”
The Highway 89 bridge crosses the Saugeen River at the eastern edge of Mount Forest and falls under the connecting link program through the Ministry of Transportation.
The BM Ross engineering report stated related deck deterioration of the bridge. The firm was informed on July 19 of a crack pattern and depression over the deck.
Township staff filled the depression with cold-patch asphalt and are monitoring the condition daily.
Observers have seen no movement due to tire truck loads, “But everyone agrees that it appears that a localized deck failure is occurring,” Williamson said.
A structural inspection was completed by BM Ross last October.
“At that time there were pavement cracks in various areas over the bridge but no pavement depressions were observed,” Williamson said. “There was an unusual pattern of pavement cracks, but no depression was reported.”
As a result of the 1988 report, a council saw to it that patching and repairs were done to the deck, as well as waterproofing and paving. The current areas of concern are adjacent to the 1988 repair areas and are not centred over of them. There may be some overlap with the 1988 patches.
During the 1988 repairs, the highway was closed and traffic detoured south of the river to Highway 6.
Prior to the 1988 repairs, BM Ross completed a review and analysis of the structure based on the 1969 plans. Engineers determined the bridge had been sufficiently designed so that it could carry prescribed loads from the Bridge Code in effect in 1988.
However, the wooden falsework used to support the wet concrete of the deck is still encased in the voids of the bridge. The voided slab construction prevents any observations of the deck soffit, so that the deterioration is completely hidden.
The BM?Ross report stated, “It is difficult to make a precise determination of the problem since the concrete is hidden under the asphalt.
However, the depressed condition indicates a punching failure of the deck. Since the deck is designed to be 229mm thick and very heavily reinforced, we can conclude that the concrete has likely deteriorated due to salt effects on the concrete and the reinforcing steel. It is our opinion that this condition is unlikely to result in a general failure of the bridge span.”
The report added, “However, it is quite possible that the punching failure of a deck segment will make the bridge unserviceable until repairs are made.”
The 1988 repairs were required when the bridge was 19 years old. It has now been 22 years since that repair was done and such deterioration may be expected, the report stated.
The waterproofing membrane should have prevented further chloride and water ingress to the concrete, but the chlorides introduced between 1969 and 1988 will still be in the concrete.”
The engineering report stated, “In our opinion, repairs are required immediately. The areas of deck cracking and depression could develop quickly into isolated areas of deck failure and the municipality should be prepared to close the bridge to all traffic until repairs have been completed.
The firm recommended “the entire deck be stripped of pavement and waterproofing membrane so that the extent of damage can be determined.
If conditions are bad, the road may then need to be closed or one lane may need to be closed. Such provisional preparations would need to be ready on the day of asphalt removal. Small deck failures might be bridged with bolted steel plates until a contractor could be hired to make permanent repairs.
Williamson said that the settlement in the asphalt of the bridge deck was noticed about a month ago. Staff filled that depression with asphalt and the pavement level dropped again.
“We’ve been monitoring it … and it seems once a week, we have to refill it. It’s asphalt over concrete – so what it is telling us is that it is collapsing underneath the asphalt.”
He noted the engineer’s report recommends stripping the entire bridge deck of the asphalt and waterproofing to find out what the problem is with the deck.
He said the problem in doing that is considering the timeframe for investigation, call tenders, and get the work, it would be impossible to complete the project this fall.
“The other issue is that the bridge is a connecting link project, which the township gets 90% funding for. All money from that fund has been designated for other projects this year.”
He said, “Our hope is to find out what the problem is with this deck, and apply for the funding next year to do the repair.”
He said BM?Ross is drafting an invitational tender to have the bridge inspected where the patch is settling, to find out what is happening.
Williamson said there is the potential of another area of the decking that will need to be dealt with as well.
“That work could be completed this fall, but it would have to happen as soon as possible.”
“If we do nothing, the old bypass (on side streets south of the river) would become the bypass for all of this winter. That would not be good for anybody.”
“The reality is we have no idea what these costs will be until we get the asphalt up and the membrane up to see what is happening beneath the surface.”
The advantage of doing just the investigation and patching, he said, is that there would be fewer costs to carry over into the new year.
And doing the investigation now, will justify the work proposed in the application to MTO, Williamson said.
He anticipated that work will include complete stripping the deck and restoration.
Williamson said the suspicion is a lower layer of concrete has deteriorated, which, in turn, is causing the upper layer of concrete beneath the pavement to fail.
Councillor John Matusinec asked if the bridge now requires additional structural inspection.
Williamson said it is being monitored.
“The bridge itself is not going to collapse. It is the deterioration of the deck which is the concern. It’s not a matter of the bridge falling into the river.”
The area being patched is roughly eight feet by 20 feet and Williamson added the depression is only a few inches deep.
Councillor Dan Yake said Williamson has been on top of the problem since it was first discovered.
Council’s resolution was to amend the 2010 budget to include the engineering and associated costs for the bridge work.
