April 17, 2013
Port Mann Bridge builders honoured as demo starts
Two plaques were unveiled at the Port Mann Bridge recently to mark the opening of the new crossing, while the demolition of the old structure gets underway.
“Thousands of builders, designers and visionaries were responsible for the construction of this new crossing, and this plaque will serve as a permanent reminder of our gratitude for building the widest bridge in the world and reducing our daily commute,” said Minister of Transportation and Infrastructure Mary Polak.
A 1964 commemorative plaque from the original bridge and a new plaque will be mounted along the new Port Mann Bridge pedestrian and cycling path once the bridge is completed to its full 10-lane width.
The new plaque reads: “Dedicated to the thousands of builders, designers and visionaries responsible for the Port Mann / Highway 1 Project - the largest transportation infrastructure project in British Columbia’s history; December 2012”.
The Transportation Investment Corporation is undertaking the demolition of the old Port Mann Bridge, which involves removal of the superstructure, substructure, piers, and footings down to the Fraser River.
Construction crews are currently focusing on the portions of the old bridge that overlap with the area to be occupied by the new bridge.
This demolition is required to complete construction of the new bridge to its full 10-lane width, as well as continue highway widening and interchange improvements through Coquitlam, Burnaby and Vancouver.
The Port Mann Bridge Demolition CEAA (Canadian Environmental Assessment Agency) Screening Assessment provides details about the demolition.
It was necessary because dredging requires Fisheries and Oceans Canada authorization under the federal Fisheries Act.
Dredging will be used to develop marine access immediately upstream of the existing Port Mann Bridge to a depth of about four metres.
In addition, pile driving is likely to be required to construct one or two offshoots from the temporary trestle that is currently being used for construction, in order to position land-based cranes.
Demolition of the superstructure involves the dismantling and removal of the steel tied arch, which is expected to begin with the removal of the bridge deck and asphalt.
Span components such as barriers, railings, electrical conduit and other items incidental to the structure will then be removed as necessary to reduce the weight on the steel frame prior to its removal.
The main steel tied arch section of the bridge is expected to be deconstructed using similar methods to those used to erect the original superstructure.
The removal of the center arch could occur by either lowering the entire arch to a barge in one piece or by systematically removing smaller sections.
The contractor is expected to remove the structure in the largest pieces possible to minimize work at elevation.
The steel deck sections, the structural steel arch and the deck framing will be removed on a panel by panel basis and hoisted by mobile cranes, which will work from the receding bridge deck.
The demolition of the approaches is expected to proceed on a span-by-span basis, working away from the connections to the steel tied arch structure at two piers.
At any particular location, demolition will start with the removal of the concrete deck followed by the supporting steel superstructure, which mainly comprises steel girders known as “stringers.”
The steel superstructure of the approach structures will be removed in two phases; removal of the section of the steel girders between pier supports, followed by removal of the remaining girder section located immediately above the pier.
Deconstruction of the substructure will involve sequential removal of pier caps, columns and pedestals, with removal to mudline elevation.
This corresponds to the elevation of the top of the pile caps, which are expected to be left in place.
Removal of the concrete substructure, including pier caps, columns and pedestals will be accomplished by: (1) wire-cutting or saw-cutting the concrete into sections small enough to be handled by a crane, and then hoe-ramming the concrete to rubble; (2) breaking the substructure apart by controlled blasting; or (3) a combination of the two options.
Prior to commencing substructure demolition, temporary cofferdams may be constructed around each pier to isolate the demolition area from surrounding river flow.
If substructure demolition occurs below water without the use of a cofferdam, wire-cutting would be undertaken by divers.
Once the underwater wire-cutting operation has been completed, divers would connect the concrete blocks to a crane for hoisting onto a barge and transport to an upland disposal site.
One pier pile cap will remain in place as intended in its original design and construction since it is integral to the non-standard south shore dike and necessary for the stabilization of the shoreline and protection of the adjacent CN rail yard.
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