Colebrook Road Overpass provides critical north-south link across City of Surrey

The Colebrook Road Overpass in Surrey, BC provides a critical north-south link across the city. Part of the Greater Vancouver Transportation Authority (TransLink)’s Major Road Network (MRN), the structure was built in 1974 with a 50 year service life. However, in less than 30 years, the structure had begun to exhibit signs of accelerated concrete deterioration in the deck, deck joints, and concrete components below, resulting from elevated chloride ion (salt) concentrations. In addition to the need for rehabilitation, the bridge was identified as a priority for seismic assessment and retrofit. The City of Surrey retained Associated Engineering to complete a detailed bridge assessment and seismic analysis, develop a rehabilitation strategy, and design seismic upgrades.

The two, parallel, two-lane bridges consist of eighteen precast, prestressed concrete girder spans supporting a cast-in-place concrete deck for each bridge span, a total of ten girders support the deck, five carrying the northbound traffic and five carrying the southbound traffic. Each span is approximately 21.3 metres long with a total bridge length of 384 metres.

The key components of the rehabilitation and retrofit program included:

• Completing the critical deck rehabilitation and improving seismic performance
• Retofitting shear keys on the 17 four-column bents
• Retrofitting tie beams between columns
• Enhancing column shear capacity near the cast-in-place concrete pile cap
• Enhancing sliding resistance of the north end cast-in-place concrete abutment.

The seismic assessment and retrofit adopted a displacement-based design approach. Two and three dimensional models were developed for the structure. Response Spectrum Analysis was used to assess the displacement demands on the structure. Non-linear pushover analysis was used to assess the displacement capacity of the various bridge components. Each retrofit option was modeled, allowing the effects of the retrofits to be assessed and refined to maximize the benefits.

The deck joints were replaced with cast-in-place concrete link slabs. The bearings were replaced with laminated rubber bearings, some of which incorporated transverse shear keys. Link slabs provided an effective waterproof joint at each pier, and provided robust structural continuity to the bridge deck, allowing the deck to better distribute the seismic loads. The new bearings incorporating the shear keys replaced the rubber bearings and provide a durable bearing and a positive load path for seismic loads into the piers. The new bearings were also designed to accommodate the accumulated longitudinal thermal deformations that result from the link slab continuity.

The new concrete pedestals for the bearings and shear keys were incorporated into the concrete repairs to the pier caps. The concrete work required to install the bearings and shear keys did double duty by addressing some of the concrete rehabilitation requirements, providing an efficient, cost-effective solution.

“We developed the rehabilitation and retrofit strategy to fit with the City of Surrey's asset management program,” advises Project
Manager, Shane Cook, P.Eng. “This involved designing repairs and rehabilitation to suit staged construction and availability of funding from the City and TransLink.”

Completed on time and on budget, the project also incorporated sustainable features such as a new bicycle path and recycling of milled concrete for use on a neighbouring farmer's lanes.

Associated Engineering receives BC Deputy Minister’s Award

The BC Ministry of Transportation presented Associated Engineering with the Deputy Minister's Finalist Award for the Beaton Canyon Bridge and Road Widening project. Presented by Kevin Falcon, Minister of Transportation and John Dyble, Deputy Minister of Transportation, the award recognizes excellence in design and contract preparation for structures.

Beaton is located in southwestern BC. The community’s only access is along a winding gravel road on a steep mountain slope. A section of the access road had eroded away. The resulting road narrowing made driving difficult, particularly for truck traffic.

The BC Ministry of Transportation retained Associated Engineering to develop a design for the road widening, including a bridge structure. The terms of reference for this challenging assignment stipulated a short construction window, and required that access to Beaton could only be disrupted for short periods of time. In addition, the steep mountain slopes limited construction activities.

Led by Project Manager, Leslie Mihalik, P.Eng., Associated Engineering developed a precast bridge design, including precast
abutment cap-beams and wing-walls. “The precast elements facilitated rapid construction,” Leslie advises. “We designed mini-piles to support the bridge and spaced the piles widely apart, which helped to accommodate traffic during construction.” Rock
anchors, drilled into the mountain slope, provide lateral stability.

Congratulations to the team including Leslie Mihalik, Alfred Kao, P.Eng., and Stephen Pienaar.