AWARD OF MERIT: Frontage Road Bridge System for Pearson Airport Terminal

Category: Transportation

HATCH MOTT MACDONALD

Hatch Mott MacDonald of Mississauga, Ontario engineered the road bridge system that serves as the frontage to the new terminal at Toronto’s Lester B. Pearson International Airport. The bridge system was completed in December and serves as the main access and staging area for the rest of the terminal’s ongoing construction. Hatch Mott MacDonald is responsible for the civil, aviation and bridge engineering components of the New Terminal Development, as part of the overall design team: Airport Architects Canada.

The road bridge system is a curved structure of 500 metres that consists of an at-grade service road, and elevated roadways at Levels 1 and 3 of the terminal building. The complete deck system is integrated into the terminal building, and the elevated decks are staggered such that the inner Departures level also acts as a roof structure over the Arrivals hall below.

Each level of the road system has an inner road of three traffic lanes for commercial vehicles and an outer road of four lanes for public traffic. In the elevated levels, light and ventilation wells are strung between the inner and outer lanes, except where there are pedestrian and vehicle crossover areas or pier-beam locations.

Structurally the bridge consists of 1000-mm deep solid post-tensioned concrete decks, continuous over three spans. The slender columns are continuous from the upper Departures level down through the Arrivals level, to caissons socketed into bedrock.

The client required that the road bridge should have a design life of 50 years and not require the normal bridge maintenance activities. To meet this need, the engineers championed the first large-scale application of cast-in-place high performance concrete for bridge construction. They incorporated previous data, specifications and experience gained from other projects and industry research to date.

High-strength concrete has been used successfully in high-rise buildings for two decades. It has also been used in precast, prestressed bridge girders, since in precast manufacture, quality control and conditions are more consistent. Large-scale, high-performance precast concrete has been used in the Confederation Bridge, St. Clair River Tunnel and Sheppard Subway Tunnel liners, the latter two designed by Hatch Mott MacDonald as well.

However, the use of high-performance concrete in cast-in-place bridge construction is slower to take place. In Ontario, as with many other jurisdictions, the Ministry of Transportation had limited its use to concrete deck slabs or pre-manufactured girder systems as part of its own trials and implementation program. This project showed that the technology can be used at a large scale; over 30,000 cubic metres of high performance concrete were successfully laid.

The physical composition of high performance concrete presents key differences to normal concrete mixes, and hence dictated strict specifications and on-site controls in the way the mixes were delivered, placed, finished and cured. For example, the most critical requirement is its immediate and sufficient curing. As soon as the surface was finished, a continuous fog mist had to be provided and wet burlap placed on the surface. The burlap had to be kept moist for seven days, and the temperature had to be carefully maintained during this time to below 70 C, with a maximum differential of 20 C. The specifications required a minimum compressive strength of 50 MPa at 28 days, type 10SF (8-10% silica fume) cement with up to 25% replacement with fly ash, slag cement or a combination, and the use of a superplasticizer.

The completed road bridge structure is deceptively simple and clean in form, when, in fact, a number of technical constraints called for imaginative engineering. In particular, the widths of the lower roadways dictated a large transverse spacing between the pier columns, which in conjunction with the split inner and outer decks, required a unique integration of transverse and longitudinal post-tensioning. Span lengths and structural depths were also constrained by the need to integrate the structure with that of the terminal building.

Because the bridge structure is so critical to the ongoing construction of the terminal, the engineers considered constructability aspects in their design. To speed up the process they also suggested that the owner should put tenders out for the work when only 60% of the drawings were complete. The project was successfully completed by December 2000, built within 18 months, on schedule, and within the $27 million budget.CCE

Project name: Frontage road bridge system for Pearson Airport New Terminal, Mississauga, Ontario

Client: Greater Toronto Airports Authority

Award-winning firm: Hatch Mott MacDonald, Mississauga, Ontario (bridge engineering consultant)

Project team leaders: Ken Bontius, P.Eng., Christopher Solecki, P.Eng.

Prime consultant: Airport Architects Canada