{"id":23986,"date":"2023-03-01T13:07:46","date_gmt":"2023-03-01T18:07:46","guid":{"rendered":"https:\/\/www.parsons.com\/?post_type=project&p=23986"},"modified":"2023-03-22T14:05:38","modified_gmt":"2023-03-22T18:05:38","slug":"canal-lachine-bridge-montreal-canada","status":"publish","type":"project","link":"https:\/\/www.parsons.com\/project\/canal-lachine-bridge-montreal-canada\/","title":{"rendered":"Canal Lachine Bridge \u2013 Montr\u00e9al, Canada"},"content":{"rendered":"
The new Canal Lachine Bridge in Montr<\/strong>\u00e9al, Canada, designed by Parsons, <\/strong>is the first curved extradosed bridge with multiple steel box girders and a composite concrete deck.<\/strong> The clearance envelope for the canal, in combination with the given Profile-Grade-Line (PGL) and the meaningful crossfall of 6%, were decisive for the superstructure concept, which had to bridge an 88-m (289-feet) long main span with an only 2-m (6.6-feet) deep girder along the inner curve. This requirement corresponds to a slenderness of 44 (span-over-depth ratio), which is remarkable for traditional beam superstructure types.<\/p>\n The reference concept was anticipating a cable-stayed bridge with two large and torsionally stiff steel box girders to satisfy the performance requirements. Hereby, a wide-cantilevering deck was selected to guarantee the 6% crossfall and maintain the clearance envelope below. In addition, a lightweight orthotropic steel deck and a tower separated from the superstructure were proposed.<\/p>\n During the bid phase of this Design-Build Project, the orthotropic deck was found to be more expensive and challenging to design, fabricate, and construct than a traditional concrete deck. Therefore, it was decided to investigate the concrete deck option. The heavier concrete deck increased the problems for the slender girders from a demand and deflection perspective. The team realized that simple steel plate girders could not meet the design objectives regarding constant girder depth and slenderness.<\/p>\n Another challenge the team overcame was live load deflections. The slender girders along the inner curve would have significantly deflected and twisted the cross-section if torsional stiff box girders were omitted. However, the two box girders proposed by the reference concept were costly and too large to be shipped. For fabrication and construction reasons, it was decided to investigate multiple small box girders tied together to form a mega steel grillage system that provides simplicity, repetition, structural redundancy, and stiffness (see Figure 1).<\/p>\n Parsons\u2019 engineers took advantage of the fact that in a curved superstructure and hyperstatic structural system, the lack of vertical bending stiffness can be partially compensated by providing torsional stiffness and capacity. To realize this effect, take your arm and bend it at a 90-degree angle. A bending moment at your wrist turns fully into a torsional moment at your shoulder and vice versa. Structural engineers know that the forces (moments and shear) in hyperstatic structural systems depend on the bending stiffness distribution in the system. This is no different for bending and torsion in a curved hyperstatic system where the torsional stiffness of box girders directly effects the bending moments and helps to redistribute high local demands in one box girder if multiple coupled box girders are used. This effect was the solution for the Canal Lachine Bridge because it allowed a concrete deck without compromising the performance criteria and the architectural vision which follows the Millau Viaduct in France.<\/p>\nInnovation in Bridge Design and Construction<\/h3>\n
Overcoming Challenges<\/h3>\n