Portland International Airport (PDX) in Oregon has begun the installation of a seismically isolated roof structure over the central area of the main terminal, which is being expanded to increase the airport’s annual capacity to 35 million passengers.
Heavy-lifting contractor Mammoet was contracted to transport and install 20 roof panels of five distinct types at the airport in Oregon while avoiding passenger disruption. The roof, crafted mainly from regionally and sustainably sourced wood, was fully prefabricated between the active runways of the airport over the course of a year. Prior to being moved, the roof panels were disconnected into football-field-size pieces to be transported to the new terminal, which is being expanded. This enabled the airport to carry on as usual while minimizing disruption to airport operations. Depending on the type of panel, each was launched, rolled into place, set directly with self-propelled modular transporters (SPMTs), or lifted with a crane into its final position.
The panels vary in weight between 40t and 632t, with dimensions up to 72 x 50 x 6m. Mammoet used four towers of Mega Jack 800 to jack up the roof panels to approximately 17m to enable SPMTs with falsework to be driven underneath each roof section. At midnight on the day of each move, the runways were closed for the one-mile transportation of the panel from the laydown yard to the terminal. The roof sections were moved with care at a speed of about 1.6km/h (1mph).
Most panels needed to be installed over the top of populated areas of the existing terminal building. To ensure the safety of the project, work was done during strict overnight closures when the public could be kept clear of the work area. Once the area was verified to be clear of all pedestrians, the installation of the roof panels could begin. Each panel, referred to as a super cassette, was installed using stationary skidding propelled by strand jacks and lowered with the skidding jacks onto column isolators. The next set of panels was then rolled into position down the bottom flanges of the previously set panels. The panels were safely secured with consideration for potential elevated wind and project-specific seismic requirements before the public was allowed to reoccupy the area below.
According to the airport, a major complexity of the project was the wood material used in the roof panels’ construction. Deflection of the roof panels was a major concern of the client and the roof designers, so at each point in the jacking, transport and installation process deflection of the roof was monitored and kept within stringent criteria. Only the super cassette pieces had steel girders in the longitudinal direction to support the 25m wooden arches and to ensure the panels could be launched using stationary skidding equipment. Also, the supports for the launching jacks were temporary towers supported by wooden piles which were installed in the 1950s.
To mitigate any issues, Mammoet performed extensive friction testing in its Rosharon, Texas, yard prior to execution to ensure no structural damage occurred to a mockup roof panel, and that the design values presented to the client for strand jack anchoring were realistic. When executing the job on-site, Mammoet closely monitored the loads and deflections to ensure that they were in line with the tested values.
To date, Mammoet has successfully placed 16 panels to wrap up phase one of Portland International Airport’s project. Four additional panels will be installed in 2024 during phase two – once the interior of the new terminal expansion has been built out by the client for general occupancy.
To find out more about Portland International Airport’s latest developments, click here.