The suspension cables of the Pierre Laporte Bridge in Quebec are becoming less and less resilient and some could fail at any time, according to information from the Enquête program. According to the Ministry of Transport (MTQ), despite worrying data and repeated reports from its experts, there is no emergency that does not yet envisage a complete replacement in the short term.
At the request of the MTQ, the five lines removed from the Pierre Laporte Bridge and replaced in the last two years have been tested in the Polytechnique Montréal laboratories.
Each hanger consists of two vertical steel cables connecting the two huge suspension cables to the bridge deck.
Enquête has received videos and test results showing the lowest resistances ever seen since the first tests conducted on traveling cables in 2015.
Two of the five lines were urgently replaced last fall and one of the cables had lost 57% of its original strength. He was down to 43% capacity, the worst result to date.
The test consists of gradually pulling each wire until it breaks, which allows you to determine its residual resistance.
Lines have been tested at Polytechnique Montréal for the past few months
A report signed by two MTQ engineers, prepared after these tests and obtained by Enquête, shows results showing a significant and accelerated decrease in the resistance of the lines. Damage and capacity loss are evolving and will continue to evolve at an accelerated rate, they say.
We learn in this document that the cables of the 160 suspension cables of the Pierre Laporte Bridge are checked during the general inspections of the bridge, but that certain parts are inaccessible and it is impossible to know their real condition without removing them.
The latest visual inspections and current tests confirm it: These cables are increasingly rusting.
You see broken steel wires on page 43 of the MTQ report Photo: Radio-Canada
This more than 100-page report was sent to managers and senior department officials on April 21. However, according to our information, they had been informed about the weak results of the stress tests long before receiving the document.
The authors recommend replacing all lines. The sooner the better, they write, some need to be dealt with at short notice to avoid emergency replacements or significant impact on bridge operations.
They also mention in the report the risk of a cascade failure given the uncertainty about the condition of the lines. If a cable gives way, the engineers explain, the adjacent cables must be able to withstand the strain.
The redistribution of load to damaged adjacent elements can cause the latter elements to rupture etc. up to a possible general rupture of the lines.
“It is absolutely essential to avoid the rupture of one or more lines with the unlikely but potential end result of a catastrophic rupture of the cascade […] which could ultimately lead to the collapse of the structure. »
— A quote from an excerpt from the report on the suspension system of the Pierre-Laporte bridge
It is difficult to estimate how quickly the damage will progress. Management of the risk of line breakage is unacceptable over a long period of time.