September 30, 2011

KENAIDAN CONTRACTING LTD.

How concrete is used to overcome constraints of a very tight site in Uxbridge will help in reaching LEED Platinum.

FEATURE | Concrete/Masonry

Uxbridge, Ontario office building site presents construction challenges

DAN O’REILLY

correspondent

Approximately 4,000 cubic metres of cast-in-place concrete will have been consumed by the time construction is completed on an innovative 40,000-square-foot, four-storey office building in Uxbridge.

Project completion is expected in October 2012 but it is not so much the amount of material that makes the First Leaside Securities Head Office noteworthy. Rather it’s how concrete is being used to overcome the constraints of a very tight and irregular site and, in the process, help the building achieve LEED Platinum status.

It was designed by RDH Architects Inc. and is being built by construction manager Kenaidan Contracting Ltd. The LEED consultant is Jain & Associates Ltd.

Located immediately south of Brock Street in the downtown core, the site is comprised of two halves whose curved and angled configurations were dictated, in part, by a heritage railway line that runs between them. The building is on the east side of the York-Durham Heritage Railway line and the parking area is on the west side.

KENAIDAN CONTRACTING LTD.

At peak of construction the project will have an average of 120 cubic metres of concrete poured weekly, estimate stakeholders.

“Concrete was really the only material that could be used (for its construction),” says Weimin Liang, project manager, exp Services Inc., the structural consultant.

A raft form foundation is being used for the building whose concrete features include a silo that will house a steel spiral staircase, a three-storey cantilevered stairway connected to the roof beam via HSS hangers and a “crash wall’ to protect the building in the event of a train derailment.

Using concrete also provides the structural support for three tiered green roofs that will include full height trees, says Liang.

The green roofs are just one component of a rigorous green design and construction package being implemented by the designers and builders in their goal to achieve LEED Platinum. As part of that strategy, the concrete will have a 25 per cent slag replacement, says Liang.

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Such a high level will create some challenges with curing times as winter approaches, acknowledges Kenaidan project manager Benjamin Alves.

“We are cognizant and mindful of the need to make smart choices as to where we obtain materials to meet the LEED requirements.”

The project is in its very early stages, but concrete formwork subcontractor Structform International has completed the erection of the 71-metre-long, 2.3-metre and one-metre-thick crash walls, which are comprised of a number of six-metre deep caissons placed every 2.4 metres. The construction took three weeks to complete and required 17 pours, says Alves.

At the peak of construction Structform will have anywhere from 25 to 30 employees on site and on a weekly basis an average of 120 cubic metres of concrete will be poured, he estimates.

For the raft slab foundation there will be two main pours with a small filler strip. Each pour will be completed as a continuous pour of 650 cubic metres for that day. Similarly the suspended slabs will also be divided into two main pours with a filler strip.

As some sections of the building will feature architecturally exposed concrete, special precautions will be taken.

“Extra care will be taken by the carpenters to ensure the formwork panels are aligned correctly and butted tightly to ensure that seams, once poured, are pleasing in appearance,” says Alves.

Along with good formwork practices, self-consolidating concrete is being used to ensure that a high-end architectural finish is achieved, he explains.

On an overall basis the project is one punctuated by a series of major challenges. Not only is the building adjacent to the railway line, it is also close to the Uxbridge Brook and that requires stringent and ongoing soil, erosion and remediation measures.

The tight building site on the east side of the railway line also leaves little room for parking and laydown areas for materials. Since there is an elementary school nearby, any truck deliveries have to be made when children aren’t walking in the area, says Alves.

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