As part of its terminal expansion project, a new, seismically isolated, roof has been constructed over the central area of Portland International Airport (PDX).
Utrecht, Netherlands-headquartered Mammoet was contracted to jack up, transport, and install 20 roof panels of five distinct types at the airport – 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 for transportation. This enabled the airport to operate as usual, with minimum disruptions. Depending on the type of panel, each was launched, rolled into place, set directly with self-propelled modular transporters (SPMTs), or lifted by crane into its final position.
The panels vary in weight between 40and 632 tonnes, with dimensions up to 72x50x6m. Mammoet used four towers of Mega Jack 800 to jack up the roof panels to approximately 17m to allow 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 transport of the panel from laydown yard to terminal. The roof sections were moved with care at a speed of about 1.6km per hour.
Most panels needed to be installed over the top of populated areas of the existing terminal building. Work took place during 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 were 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 were allowed to reoccupy the area below.
Work on the new roof took place during overnight closures
Complex materials
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 allow the panels to be “launched” using stationary skidding equipment. 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 mock-up 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 sixteen panels to wrap up phase one of the 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.
Image: Mammoet
