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McIntosh Perry

Rehabilitating a dozen bridges in 12 months:

McIntosh Perry solidifies leadership in bridge innovation

One of the most recent projects completed by McIntosh Perry saw the firm not only incorporate new bridge innovation, but also complete an advanced assignment six months ahead of schedule.

McIntosh Perry put the finishing touches on a 12-bridge innovation in July, wrapping up the project with the Ontario Ministry of Transportation (MTO) in only 12 months. But that’s not all. The ever-evolving firm also put a new design in place that will increase the longevity of the bridges it rehabilitated.

Bala Tharmabala, Head of the McIntosh Perry Bridge Engineering Office in Burlington, Ont. said the move earned the firm praise from its client, helping further advance McIntosh Perry as a leader in bridge innovation.

More than a year ago, the multi-disciplinary engineering and related professional services firm was tasked with carrying out the rehabilitation design of a dozen post-tensioned voided deck-type bridges, with very large deck end skews of 30 to 45 degrees.

The engineers on the job used a new approach to develop semi-integral details for bridges having a large skew. “By adopting this approach, and with careful detailing around the skew deck end, we were able to complete the rehabilitation design with assurance that the rehabilitated structure will perform another 40 to 50 years without need for another extensive rehabilitation,” Tharmabala said.

Tharmabala noted although the common approach for rehabilitating the deck ends would mean replacing the existing expansion joints with new joints, it may not be the most appropriate treatment to achieve long-term durability. “It is well known that expansion joints leak with time and the deck will start deteriorating further a few years after the completion of the expensive rehabilitation work,” he said.

Given the bridges involved extraordinarily large skews, the McIntosh Perry engineers were faced with the decision to maintain the status quo and stay with tradition - or to design a new method to augment the future of the structures.

“We had to create a way to go through the process. Our designers persevered to come up with a detail that will allow the bridges to be converted to semi-integral articulation arrangement,” he said.

To do so, the new design shifts the expansion joints further away from the deck ends. In addition, it also sees the approach slab move directly over the deck ends and incorporates shifting the ballast wall to form a gap between it and the deck end. This methodology allows the deck end to move freely without touching the soil and thereby not be affected by the forces of the backfill induced by the thermal expansion/contraction cycles, which could possibly rotate the bridge after a few years of service. Tharmabala said this new design was enhanced by the addition of a sleeper slab, allowing free movement of the approach slab while the corners were able to function without damaging the approach pavement.

Not only is the firm earning praise for its advanced design, but the project was also completed a full six months ahead of schedule. The work originally started with an anticipated 18-month timeline. As it progressed, Steven Pilgrim, project engineer with McIntosh Perry, said the staff made an extra commitment to see the project through in a timely manner – and exceed expectations.

 “We had a great staff who was able to dedicate time beyond what was required,” said Pilgrim.

Tharmabala said client reaction was positive, as the early completion means saving finances and resources. “The senior managers at MTO appreciated what we did and they appreciate the efforts we took to deliver the project six months early,” he said.

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