June 18, 2015
Category: Case Studies, Box Girders - Published by: Patrice Tremblay
The Burgoyne Bridge is a new 1,090-ft (333-meter) structure that’s being built over Highway 406 and the Twelve Mile Creek River in St. Catharines, Ontario, which is located in the Niagara Region. The two-lane structure will replace the existing bridge that was built over 95 years ago.
The new structure features two lines of 16 box girders, the longest of which measures 84 ft. (25.5 meters) and weighs 80 tons. The structure is composed of over 2,830 tons of steel, including a 410-ft. (125-meter) arch, 44 pot bearings, a number of which are being used as temporary supports to uphold the main span during construction, and 4 LG-3 type modular expansion joints.
This project presented many challenges. To start, the significant weight and width of the box girders, which are over 19 ft. (5.8 meters) wide, required technical prowess when being handled at the plant and transported to the jobsite. The construction site itself also made the erection more complex as the road sits high over the river and the access points were on steep terrain. Also, because of the height of the piers, which stand 82 ft. (25-meters) tall, it would have been both difficult and costly to erect the girders in a conventional manner, i.e. using a crane positioned along the bridge at the river level. Moreover, the space available at each end of the bridge was very limited because the erection site is located in the heart of the City of St. Catharines.
In addition to ensuring the integrity of nearby buildings, worker safety was also a major consideration since performing a conventional erection at such heights would have increased the risk of accidents.
The erection of steel components was awarded to Canam-Bridges who called upon the engineering firm Harbourside Engineering Consultants to design the appropriate method of erection. Given the aforementioned challenges, the chosen method combined two techniques: the launched-girder erection technique, which was used in the erection of the Gilbert River Bridge, and a system to unload and position the box girders that would not require a high-capacity crane.
A line of girders was first assembled behind the northern abutment and then successively pushed into place one girder at a time using hydraulic equipment. The unloading zone located behind the launching area, which was in a 10% slope, required a change to the initial concept of a craneless erection. The arrival of winter had caused stability-related problems due to the presence of snow and ice in the relatively steep slope. A small-capacity crane was therefore brought in to ensure the safety of unloading operations.
The system developed by Harbourside Engineering Consultants to unload and position the box girders required the design and fabrication of four mobile vertical supports. These supports allowed us to gradually adjust the height of the rollers from the elevation of the semi-trailer in the unloading zone to that of the launching area, which represented a difference of over 8 ft. (2.5 meters).
Once the crane was used to cantilever a box girder on the semi-trailer, it was no longer required for the subsequent steps. No external force was needed to transport the box girders to the launching area as the 10% grade combined with the low frictional resistance of the rollers allowed for the use of gravity to move the components. A pneumatic winch was used to restrain the girder while it was being lowered into the launching area.
A hydraulic portal lifting system was employed when lowering the box girders into the launching area in order to progressively adjust their height to the component ahead of it. This operation freed up space for the arrival of the next girder in the unloading zone. The splice was then bolted and the launch could begin, clearing the way for the following girder. The various unloading, positioning, bolting and launching sequences took place over a three to four-day period, depending on weather conditions.
The experience acquired in developing and executing this new method will subsequently be perfected and is already being planned for future projects. These innovations allow Canam-Bridges to be even more efficient in erecting our structures.
Owner: Regional Municipality of Niagara
General contractor: Pomerleau
Engineering firm: Parsons
Launching engineering firm: Harbourside Engineering Consultants
Drafting firm: Tenca Steel Detailing, Inc.
Superstructure and erection: Canam-Bridges
Erection sub contractor : Walters Inc.
Structural bearings and expansion joints: Goodco Z-Tech
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