Launched-Girder Erection: A Cost and Time-Effective Technique

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June 4, 2014

Category: Launched Bridges  -  Published by: Éric Lévesque, ing., M.Sc.

Canam-Bridges participated in the construction of a bridge over the Natashquan River that now links two municipalities in the province of Quebec, Kegaska and Pointe-Parent, which are located approximately 620 miles (1,000 km) north of Quebec City. Until the bridge opened in fall 2013, Kegaska residents had relied on other means, including boat, plane and snowmobile, to meet their transportation needs. This project was executed in the scope of the extension of Route 138.

The superstructure chosen for this 469-ft. (143 m) highway bridge is a continuous girder system with four lines of main girders over two spans. The primary steel structure is composed of welded girders and bracings. The 900 tons of steel components that form the superstructure, which are distributed over 28 girder sections, were fabricated at the Canam Group plant in Quebec City. The various components measured up to 105 ft. (32 m) in length and weighed as much as 30.5 tons each.

Natashquan-Pont-01
Natashquan River Bridge while under construction
Natashquan-Pont-02
The Natashquan River Bridge now links Kegaska residents to the Quebec highway system.

Launched-Girder Bridge Erection

Time and cost savings were a major concern in the execution of this project and it was partially for this reason that the launched-girder erection technique was chosen. Other factors that led to the use of this technique included:

  • Tight deadline and the desire to minimize risks
  • Limited lifting capacity needed at the erection site
  • Reduced environmental impact

Tight Deadline and Desire to Minimize Risks

The use of the launched-girder erection technique allowed for the sequential erection of the main girders, the secondary components as well as the formwork that was successively put in place prior to the different launch phases. These steps were carried out on land, thus providing very safe conditions for workers. Moreover, the optimal working conditions contributed to enhancing jobsite productivity. Typically, high-capacity cranes mounted on barges would have been used to erect the steel girders, given the worksite layout. However, this method would have been much slower and riskier, especially with regards to meeting the deadline and staying within budget.

Natashquan River Bridge

Limited Lifting Capacity Needed at the Erection Site

Given that the cost of high-capacity cranes can be quite significant, the choice of the launched-girder technique allowed for major savings as it limited the size of the lifting equipment that would be needed. The crane capacity required to perform the launches was determined based on operations to unload the components upon delivery and then place them on the assembly stands located upstream of the western abutment. Given the short-range maneuvers and the maximum weight of the components, i.e. 30.5 tons, a conventional 200-ton crane was sufficient.

Natashquan River Bridge
A conventional 200-ton crane was used.

Respect for the Environment

The Natashquan River is one of the largest salmon rivers in the province of Quebec. Keeping environmental impacts to a minimum was therefore a key consideration throughout the construction process. The launched-girder erection technique is an excellent alternative as it eliminates the possibility of spills and other risks associated with the use of barges or the construction of landings in the river to erect girders, which greatly disturbs the equilibrium of aquatic ecosystems. Moreover, the use of a smaller crane acted to reduce the overall amount of greenhouse gas emissions produced by the project.

Images of the Launch

View a video of launching operations for the Natashquan River Bridge.

An Effective Technique

The launch had to be performed on sloped terrain given the direct access to the western bank, which represented the most economical choice. This option called for enhanced restraining systems that had to be operated simultaneously with the launching system.

Thanks to this high-performance technique, the erection of the superstructure was executed in a total of three launch sequences in spring 2013, on April 23, May 1 and May 8, according to an accelerated construction schedule that ran seven days a week, 10 hours a day.

The erection of the Natashquan River Bridge is a prime example of sustainable development that answers the needs of the current population while minimizing the impact on future generations. This type of development rests on a long-term vision that takes into account the inseparable nature of social, economical and environmental considerations.

The Canam-Bridges team is proud to have participated in the execution of this project. Following this concrete example of a highly successful collaboration, we look forward to again being called upon to share our expertise in the realization of similar projects in the years to come.

Consult the project file

Project Team

General contractor: Construction Atik
Engineering firm: WSP Global Inc.
Bridge owner: Ministère des Transports du Québec

* Imperial tons

 

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