Technical Corner: Athabasca River Bridge Launch
January 6, 2010
By Canadian Consulting Engineer
Infinity Engineering Group completed the widest and one of the longest bridge launches in Canada in November, ...
Infinity Engineering Group completed the widest and one of the longest bridge launches in Canada in November, crossing the Athabasca River near Fort McMurray, Alberta.
A new bridge is being built across the Athabasca River in Fort McMurray, Northern Alberta as a part of the ongoing expansion of oil and sand developments. This bridge is being built parallel to the two existing bridges and will double the capacity of Highway 63 at its crossing of the Athabasca River.
The superstructure of the 472m-long, 30m-wide multi-span bridge consists of 10 steel plate girders with a composite cast in place concrete deck. All 10 girders are being launched simultaneously, resulting in what is believed to be the widest launch ever undertaken in North America. In addition, with the total weight of structural steel exceeding 6 million kilograms, this segmental launch is setting a precedent as the one of the heaviest steel bridge launches in North America. The girders cantilevered the maximum clear span of 76m without the use of intermediate temporary bents. An inclined launch nose attached to the leading segment of girders made touch down at the piers. Of the total bridge span, 394m length will be launched while the remaining 78m-long flared end section will be crane-erected. Surespan Construction is the erection sub-contractor for the steel girders while Flatiron Constructors are the general contractor. Infinity Engineering Group is the construction engineer for the steel erection. The project owner is Alberta Transportation, and the bridge designer is CH2M Hill.
The erection engineering consultant and contractor investigated erection options in search of the most economical method. It was determined that launching all 10 girders simultaneously offered a significant cost saving and schedule advantage. Aspects of the launch that required particular consideration and detailed engineering included the launch nose, launch pad, girder supports, pushing assembly and a review of the permanent structure. A detailed finite element model developed by the erection engineer was used to assess the girders at several critical stages throughout the launch. The staged analysis took into account the cambered geometry of the launched girders.
A launch nose with an inclined bottom flange was attached to each of the leading girders. Cross and plan braces tied each launch nose together to create a single structural system. As the girders approached each pier the bottom flange of the launch nose touched down on the Hilman rollers then acted as a guide to correct vertical alignment of the girders.
The launch pad was built of H-piles orientated in line with each girder and positioned with their flanges vertical. Solid wood blocking beneath the web of the H-pile, in combination with intermediate concrete footings distributed gravity loads to the compacted ground, while along each girder line, every segment of steel H-pile was welded together. The launch pad was close to 100m long.
All 10 girders were supported during the launch using 150t and 250t Hilman rollers. Standard 150-XNTL Hilman rollers were positioned at abutment two and at pier four while 250-XOTL-08332 Hilman rollers served at piers two, three, five and six. Lateral guides were positioned at the abutment and each pier. Several of these guides housed jacks that were used to maintain the longitudinal alignment of the girders. At the rear of each girder a steel sled beam was used for vertical support and to facilitate longitudinal movement.
Each girder sled had 25mm-thick Teflon runners fastened with counter-sunk screws to the underside of its bottom flange. These sleds were guided by, and travelled inside, stationary H-piles in the launch bed. Strand jacks were fastened to the rear of the sled beams. High strength strands were anchored at the abutment and ran along the length of the H-pile through the strand jacks. Upon activation the jacks gripped the strands resulting in a pushing force which enabled the longitudinal launch. Each girder sled was tied together with a transverse push beam, which transferred the longitudinal pushing force from the sled beams to the girders. The launch was completed on schedule on Nov 10. Just before completion the maximum strand jack force was approximately 4600 kN (10,000,000 lbs). The strand jack system was supplied and operated by DYWIDAG-Systems International Canada, Ltd.
Infinity Engineering Group Ltd. is based in North Vancouver, B.C.