Northport Bridge Replacement Alternate
Location: Cumberland County, Nova Scotia
Client: Alva Construction
Duration: 2010-2011
Key Staff: Robbie Fraser, Ghislain Doucet
Project Description
After tender and award, Harbourside Engineering Consultants was hired by Alva Construction to provide a value engineering alternate design for the replacement of the Northport Bridge that spans the Shinimicas River in Cumberland County along Route 366. The old bridge, constructed some 50 years ago, was limited to loads of 20,000 tonnes or less. This vital piece of infrastructure had to be replaced with something capable of carrying all legal highway loads.
Harbourside’s Role
The alternate design, completed by Harbourside, consisted of a 2 span semi-continuous precast concrete girder structure founded on fully integral abutments and a central in-river wall type pier, also founded on piles. The alternate design resulted in significant cost savings for the contractor, as well as the Nova Scotia Department of Transportation and Infrastructure Renewal. These savings were achieved by reducing the number of girders in the structure from the parent design, as well as significantly reducing the number of piles in the abutments by modifying the abutments from semi-integral to fully integral structures.
Unique Challenges
As a design build alternate design, the contract had already been awarded, and construction was initiated before design began. To keep the project on schedule, design drawings were issued in packages so that the design could be carried out in parallel with construction activities without influencing the overall project schedule. This required a great deal of cooperation and coordination between Harbourside Engineering and the contractor. The design of the structure was further complicated by the bridge’s proximity to the mouth of the Shinimicas River, where it discharged into the Northumberland Strait, and the fact that the pier design needed to account for dynamic ice loads. Since an ice study was not completed during the base design, Harbourside conducted a site-specific desktop ice study to determine the 1 in 100-year ice thickness and crushing strength to determine the dynamic ice loads for the design of the central in-river pier.
Social Impact
The aging bridge structure had become a safety concern for residents in Cumberland County. In addition, the loss of this vital corridor between both sides of the Shinimicas River would mean extensive detours for the local community. Harbourside’s design of the new structure ensured a speedy replacement and a much-needed renewal of the crossing. Now capable of bearing all legal highway loads, the new bridge is a welcome modernization for the area.