October 16, 2014
Category: Launched Bridges, Case Studies - Published by: Raphael Gagné
Built in the scope of the Highway 73 extension project in the Beauce region, the Gilbert River Bridge is a 1,070-ft. (326-meter) structure that was erected 170 feet (52 meters) over the Gilbert River and 34th Street in Notre-Dame-des-Pins, Quebec. The new bridge features eight lines of 11 girders, with each component measuring 11 feet (3.4 meters) tall and weighing up to 48 tons apiece.
Canam-Bridges supplied 4,550 tons of steel components in addition to Goodco Z-Tech elastomeric pot bearings and modular expansion joints for both abutments of this bridge. Fabrication, which was completed in December 2013, was carried out at the Canam Group plants located in Quebec City and Laval, Quebec.
The highway is extremely elevated in comparison to the river and the embankments are steep. With the piers standing 98 to 164 feet (30 to 50 meters) high, it would have been difficult and costly to erect the girders conventionally using a crane positioned along the river and erecting the girders one by one on temporary supports. Moreover, worker safety was another element that had to be taken into consideration as working at such considerable heights using a traditional approach would have increased the risk of accidents.
In view of the above-mentioned factors, the launched-girder erection technique was chosen. During the first phase, four lines of girders were assembled behind the northern abutment and then launched into place using the equipment supplied by Canam-Bridges; the same type of equipment had also been used for the North Channel Bridge project in Cornwall, Ontario, and the Natashquan River Bridge project in Quebec. The first of the eight launches was completed on December 17, 2013. The team launched the bridge over a distance of 55 feet (17 meters) on December 16 followed by 252 feet (77 meters) the next day, representing a total launch of 308 feet (94 meters) over two days, just as had been initially planned. Canam-Bridges is thankful to the team that accepted to work on December 17 despite the intense cold (- 33 °C at the start of their shift). It was also the first time that the hydraulic equipment was used at such cold temperatures. All in all, the first phase was a complete success despite the complications caused by Mother Nature.
The second phase of the erection was carried out in a manner very similar to the first. The four remaining lines were assembled behind the northern abutment and subsequently launched using the equipment supplied by Canam-Bridges.
During the launching sequences, the maximum distance that the assemblies could advance was 59 feet (18 meters) per hour. Including the required stops and verifications, and with optimal conditions, four girder lines could be launched close to 328 feet (100 meters) during a good workday. The launching distance was not increased as the established speed allowed for the efficient control and validation of reactions and deformations in the girder lines. Prior to each of the launching sequences, the erection teams had spent approximately two weeks assembling the girders, bracings and other required steel components behind the northern abutment.
Once the two assemblies of components that each contained four girder lines and their respective bracings were put in place, the final series of bracings connecting the two were erected using horizontally-positioned jacks. Canam-Bridges completed its mandate on June 27, 2014, a month ahead of its original construction schedule.
Canam-Bridges was able to promote solutions to facilitate the bridge erection process by using the launched-girder erection technique, all with a view to speed up the project. Thanks to the use of this technique, the bridge structure could be erected during the winter and allowed the customer to carry out certain formwork-related tasks more quickly before each launch. Canam-Bridges’ experienced technical team, which was stationed onsite and had taken part in many such projects in previous years, also shared its expertise with steel erectors and the general contractor throughout the execution of the project.
Special collaboration: François Jutras, Chief, Bridges and Bridge Infrastructures, Roche Ltd, Consulting Group
The engineering portion of the Gilbert River Bridge project was overseen by the Roche – CIMA + consortium. Given the length of the structure, the number of spans and the significant height of the piers, monthly meetings were held from the very start with the Chaudière-Appalaches regional branch (DTCA) as well as concrete specialists working at the roadway lab directorate (DLC) of the Ministère des Transports du Québec (MTQ) to ensure that the best solutions were chosen and that the specifications indicated all of the requirements that would allow for the highest possible quality. Below are the main challenges that the engineering team faced in the scope of this project.
Roche determined the height of the poured concrete piers and then validated its calculations with qualified contractors to ensure the feasibility and optimization of the formwork and rebar joints. A concept was subsequently created featuring a minimum number of joints. The massive amounts of concrete that had to be poured led Roche to establish precise criteria and requirements in collaboration with the DLC in order to limit cracking and ensure the durability of the underlying structure.
In the presence of major structural efforts, it’s necessary to use large quantities of intersecting rebars. Roche therefore created a 3D model illustrating the positioning of the rebars in the footings as well as certain areas of the piers and crossbeams to ensure that the concrete could be poured using conventional pumps without the risk of segregation.
Roche considered several scenarios for positioning the girders as well as their transportation to the jobsite. The launched-girder erection technique requires that a large number of analyses be performed to ensure that various reference values, such as bearing reactions, girder deformations, etc., are available when they’re needed. For this project, Roche elaborated a launching scenario in compliance with CAN/CSA-S6-06 to ensure that the chosen contractor would not submit a launching scenario that was difficult to validate or that would have resulted in inacceptable deformations in the permanent structure.
Afterwards, the challenge rested in elaborating launching specifications that, together with the model, would be sufficiently demanding to guarantee the quality of the erection. The specifications also took into account the impressive size of the superstructure, the length of the spans, the financial implications and the obvious safety management issues in the event of a failure or work stoppages following unforeseeable and sudden material behaviors.
The MTQ decided to integrate a deicing system on the bridge deck, the first-ever in Quebec. Controlled by a weather station, this system deices the deck when freezing rain conditions are detected. The challenge in this case was to incorporate the various nozzles, housing and accessories throughout the superstructure as well as the integration of a permanent maintenance walkway.
View a video of the launching of the Gilbert River Bridge.
General contractor: Couillard Construction Ltd.
Engineering firm: Consortium Roche – Cima +
Owner: Ministère des Transports du Québec
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