Hangar 14 Update – October 1st, 2023

One of the primary concerns regarding the future of Hangar 14 pertains to the necessary remedial work, particularly concerning the trusses supporting the roof. Our hangar is one of approximately 200 constructed for the British Commonwealth Air Training Plan during the Second World War. The roofs of these hangars are upheld by Warren trusses crafted from green Douglas Fir timber sourced from British Columbia, complemented by a cable post-tensioning system. Depending on the requirements of the base, the basic hangar design could be expanded either in width, creating two spans of 34m supported by intermediate columns, or, as in our case, both in width and length, resulting in the largest “double-double” design.

Double-Span Warren Truss Structure with Post-Tension Cables 

The Department of National Defense (DND) currently maintains around 70 Warren truss structures and has initiated multiple studies in collaboration with the Royal Military College to comprehend the gradual degradation of these structures over time, ensuring their continued usability and safety. 


One such study involved research-based investigation into the characteristics and capacity of Building H-103 at CFB St-Jean, Québec. H-103 is a double-span hangar similar to Hangar #14 but half as long. However, since the trusses span the entirety of the building, it serves as an apt comparison to our building.

Over the years, extensive remedial work has been carried out on H-103, including the installation of some intermediate steel columns to support the middle of the trusses. DND expressed concerns regarding the building’s safety in the event of heavy snow loads and implemented an evacuation procedure for snow loads exceeding 10 cm. However, they aimed to thoroughly analyze the actual structural capability of the building, devising a system to monitor deflections in the trusses during heavy snow loads, and to understand the strengths and weaknesses inherent in the Warren truss system. 


During two major snowstorms in 2019 and 2020, with snow accumulation reaching depths of 23cm and 35cm respectively on the roof, no significant deflections were observed. All deflections remained well within acceptable limits. Most of the structural members conformed to both the National Building Code of Canada and the Canadian Timber Design Manual. However, strain data on the individual components of the trusses revealed that one Double Diagonal Web member exceeded compression limits. This issue was attributed to the installation of intermediate steel columns, which had caused load reversal in several components of the trusses, including these Double Diagonal Web members. In other words, some components designed for compression were now under tension or vice versa. Hangar 14 does not have intermediate columns installed, so similar issues with load reversal should not arise. Nonetheless, understanding the condition of the roof trusses is crucial moving forward. 


An Automatic Total Station (ATS) installed in H-103 collected vertical, transverse, and longitudinal deflection data from October 2018 to March 2022. The ATS revealed cyclical annual movement of the entire building due to varying humidity levels. Importantly, all deflection values remained well within allowable limits, even during major snow events. Consequently, it was concluded that the 10cm snow depth evacuation limit was unnecessary. 


As part of the City of Edmonton’s assessment of Hangar 14, they enlisted BPTEC Engineering to conduct a structural investigation of our Warren truss roof. The purpose was to ascertain the long-term structural capacity of our building and identify necessary reinforcements. Their study, conducted between 2018 and 2019, identified specific structural members that had failed, cracked, or exhibited significant wear. Considering potential increased snow loads due to developments around the building related to the Blatchford development, they recommended reinforcing all (546) truss joints, replacing 146 truss compression members, and replacing 186 truss members, along with all post-tensioning cables. This undertaking would be substantial, prompting us to collaborate with Ian Morgan at Next Architecture to engage BPTEC for a comprehensive review of their recommendations in light of data from Québec. We may explore the possibility of installing intermediate columns as a means of reinforcing the roof structure, but we must take care to avoid load-reversal issues, as experienced in H-103. 

Depending on the recommendations, we are also considering the installation of a continuous monitoring system to provide real-time information about the condition of the roof structure. Implementing such a system, along with having the data reviewed by an engineering firm, can be costly – on the range of $350,000 over the first two years, and $50,000 per year thereafter. Therefore, we are exploring various funding options and alternatives, including potential partnerships with research institutions, to ensure the best return on investment. 


Once we receive further information from Next Architecture and BPTEC, we will share the results with you.