No matter how carefully work is planned, sometimes designs don’t easily translate into reality. Often, the more sophisticated the design, the more difficult it is to render into actual form. In the case of one very modern, innovative design for a pedestrian/cycle bridge, laser scanning helped keep the project on-time, on-budget and aided in turning the design into reality. By employing terrestrial LIDAR, material scrap rates were significantly reduced and project delays were kept to a minimum.
Implementing a Transportation Solution
The City of Pickering is a rapidly expanding suburban city of 90,000 people approximately 20 miles (32km) east of downtown Toronto, Ontario, Canada. Because the Toronto "region" is a sprawling metropolis of about 5 million people, large highways and mass transit are essential commutation conduits to and from the downtown core. Pickering sits just on the north shore of Lake Ontario and is bisected by Highway 401 (the busiest highway in Canada and one of the busiest in all of North America), as well as major passenger and freight rail lines.
In 2011, with funding from multiple levels of government and the provincial rail agency, Metrolinx, a bridge project was undertaken to provide pedestrians, cyclists and commuters with the ability to easily traverse these major east-west transportation corridors in a comfortable and, some might say, stylish fashion. (See Figure 1 for an example of the artistic nature of the design.) At over $20million (CDN) the span is intended to help connect the City of Pickering to the major transportation systems in Southern Ontario, and is eyed as an impetus to help transform the downtown area of the city by creating pedestrian access across the transportation corridor. Additionally, the bridge is designed to allow easy access to the commuter rail station/platforms, parking lots and shopping centers that are adjoining the highway and rail lines.
Modern Design and construction Methods
AECOM Canada is responsible for the overall design and construction of the two-phase project, with Teeple Architects providing the preliminary design and APlus General Contractor acting as the lead construction firm. AECOM used Revit Building Information Modeling (BIM) software to model the complex design and employed Integrated Project Delivery (IPD) techniques for construction. BIM-dependent IPD aids in the communication with the sub-contractors/sub-trades to estimate material delivery quantities and to provide a method for feedback on design. IPD helps smooth the "hand-off" points between the trades as well.
Generally, BIM’s are leveraged throughout the design-build and even extend into the full life-cycle of the construction project continuing on as a "facilities management tool" extending into operations and maintenance aspects of the facility after completion of construction. The BIM can sometimes be used as an accurate as-built document, especially when scan data is available to compare to design and then used to update the model layers. While using BIM-based IPD makes the handoff between sub-trades much easier and minimizes confusion, sometimes there are complexities in the design where adjustment is required to meet the requirements during construction. Using a LIDAR scanner can aid in determining if there are slight discrepancies between the design model and the actual as-built conditions. This is especially helpful where tight tolerances are concerned.
A Unique Design
The fully accessible and completely enclosed Pickering Bridge is the first of its kind in Canada. It stretches over 800 feet (about 240meters). A standard truss-based steel structure with concrete flooring and membrane-on-steel-deck roof, the bridge’s interior has customized glazing that provides a comfortable interior environment. It is also the first pedestrian bridge to be covered in highly specialized perforated aluminum sheeting (cladding) called Kalzip.
Utilizing a passive ventilation approach, the Kalzip material resists solar gain, easily sheds snow/ice (before accumulating), reduces wind-loading, and due to the perforations, serves as a transmissive material for light and air. In addressing the unique construction challenges of the glazing within the structure and also the compound curves required in the design of the Kalzip cladding, it fell to the use of terrestrial LIDAR to assist in providing project cost and time savings by verifying the as-built situation for two different aspects of the construction.
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