August 19 2020
Behind the Project: Highway 427 Over Highway 407ETR
Integrating Bridge & Construction Engineering
Recently, we sat down with Jason Jelinek, Principal, to talk about one of the many interesting projects he’s worked on.
Thanks so much for chatting with us, Jason. Tell us about this project.
To accommodate the ongoing expansion of Highway 427 in Woodbridge, Ontario, the existing northbound and southbound structures over mainline Highway 407ETR required widening.
The existing structures were 94-metre-long, three-span, voided slab, post-tensioned concrete bridges. They originally carried three lanes of Highway 427 traffic over Highway 407ETR and both the northbound and southbound structures were widened to include new primary traffic lanes, HOV lanes, and increased shoulders. The existing bridges were widened by adding new structure on both their exterior and median sides.
That sounds like quite an undertaking. What was unique about this project?
The distinguishing aspect of this project was that the existing post-tensioned concrete bridges were widened with new steel box girders.
In a conventional bridge widening, the new portions of the structure would typically be built with a similar construction to that of the original bridge. But there were significant disadvantages associated with building the new widenings for the existing Highway 427 bridges with post-tensioned concrete. Post-tensioned concrete construction would have required a sizeable falsework system to be set up along active lanes of both the eastbound and westbound mainline Highway 407ETR, resulting in reduced service and increased traffic risk.
Additionally, to suit the depth of the falsework required, the widenings would have been needed to be built at a higher elevation and then lowered into their final positions, adding time and cost to the project.
Recognizing the significant disadvantages associated with constructing the new widenings with post-tensioned concrete, Entuitive developed an alternate solution of using heavy steel box girders.
The use of steel box girders eliminated the need for falsework and avoided long-term disruption to active Highway 407ETR lanes. The new steel girders along the exterior sides of the existing structures were placed using conventional cranes and the new steel girders along the median sides of the existing structures were placed with launching, with both methods only causing minimal disruption to traffic flow on Highway 407ETR during night time lane closures.
That’s a great solution to the challenge of widening the bridges. Can you tell us a bit more about integrating the post-tensioned concrete structures with the steel box girder widenings?
One of the primary technical challenges with this project was designing and detailing the new steel box girders to have similar flexural properties to those of the existing concrete structures.
Having similar flexural properties for the original and widened structures was important so that they responded similarly to the traffic loads and temperature effects and did not create excessive stress through the closure pour connection in the deck. Intricate time-dependent analysis with full consideration of creep and shrinkage was carried out to demonstrate that traffic and thermal loads could be appropriately shared between the new and original parts of the structures.
What was your favourite part of the project?
One of the most interesting and appealing components to working on the Highway 427 widening was the level of integration between bridge and construction engineering. The project gave us the opportunity to both design the permanent structure and have a significant voice in the methods that would be used to build it. There was satisfaction in seeing the new widenings being successfully constructed by the contractor using the concepts we had originally envisioned.
Launching of Median Steel Box Girder
Any final thoughts?
This project is an excellent example of how methods of construction can influence and ultimately drive the final design for a new structure. It emphasizes the importance of thinking about construction right from the onset of design.
By identifying the potential impacts of construction methods early in the design phase, we were able to develop and finalize a concept for the new Highway 427 widenings that provided minimal disruption to our client’s ongoing operations.
Thank you so much for chatting with us, Jason.
If you’d like to learn more about this project, reach out to Jason Jelinek.