KF Aerospace Centre for Excellence
Design-Build Subcontractor
The new KF Aerospace Centre for Excellence has come to Kelowna! We were honored to work with Meiklejohn Architects and Sawchuk Developments on a legacy project for one of Kelowna’s largest employers, KF Aerospace. Kelowna Flight Craft, owner of KF Aerospace, wished to create a space which both pays tribute to the 50 years of the company’s history and educates visitors on the history of flight in the Okanagan and worldwide.
Shaped as an aircraft, a central 2-storey hub “fuselage” is flanked by two wing-shaped hangars which houses historical planes. The building showcases the latest in structural innovation and mass timber construction throughout the superstructure. From wing-shaped hangar roofs to a highly unique doubly-curved CLT staircase, a creative approach to structural engineering was pivotal to the design of this project.
We joined the project team in the summer of 2020 as structural engineer of record, and our team collaborated extensively with the architect and owner, scheming efficient and elegant solutions for the different building components.
The project is now complete and already becoming a "place to be" in the Okanagan region!
Design
KF’s motif, “We’re all about the craft”, resonated immediately with our teams’ core values of innovation and craftmanship. This synergy between companies was seen early on, giving Barry Lapointe and the ownership team confidence to appoint us as both structural engineers and builders.
One of the project goals is to demonstrate BC’s local design expertise and materials, and as such the entire structure was sourced and manufactured from within BC.
For the two aircraft hangar “wings”, our structural engineering team had to answer the question: How do we create one of the most efficient “wing” building structures worldwide? Taking our cue from the aerospace industry, we used the latest in computational design to optimize structural solutions for these unique roof structures.
Hangar Roofs
The long spans of the hangar roofs presented a particular structural challenge, with folding glass hangar doors creating a 115’ clear span to allow aircraft such as the Convair CV580 and the DC10 to enter the hangars.
Our approach to this wing structure has drawn inspiration from aircraft wings of the past, including the Spitfire. Just like in an aircraft wing, we have designated the truss clear spanning the hangar door as the “spar truss”, while the trusses spanning the hangar in the other direction are the “rib trusses”.
The rib trusses set the shape of the aircraft “wings”, so we went back to aeronautical engineering basics and looked at the NACA airfoil equation. Studying the important parameters of this formula, we derived a parametric shape that could be passed into a structural analysis software. The solution space for our goal, to find the lightest wing while maintaining specific structural criteria, was explored using both evolutionary and more traditional hill-climbing optimization algorithms.
After conducting 2D studies to understand optimal wing profiles, we then implemented an optimization of the entire hangar roof structure, including the spar truss. This optimization investigated ideal positions of the rib trusses and spar truss web density.
Testing
Curved DLT Panel Testing
The DLT roof panel curvature for the mid-section was tested in the StructureCraft shop by landing the panel on top of two prefabricated jigs located near the center of the panel. To weigh down the ends to produce the required curvature, it took four people standing at each end. Figuring that this load could be replicated by ratchet straps fixed to lock blocks on site, it was confirmed that the panels would conform to the desired curvature. In its final position, the curvature would be locked in by the queenposts and cable.
Curved CLT Stair Laminations Test
Timber composite concrete (TCC) is a well-known structural element that keeps evolving. Also common in the industry is Cross Laminated Timber (CLT), a wood product commonly used as a planar element for floors or walls to carry out bending out-of-plane and shear-diaphragm forces in the plane of the element.
For KF Aerospace, we are faced with the problem of creating a spiral CLT stair (read more here). The spiral shape forces the CLT to bend around both axis (double-curvature) and carries forces in a combination of strong- and weak- axis bending as well as torsion.
Bending lumber and gluing it together (GLT) is an established method around one single axis, but bending in addition to twisting the CLT without cut-offs is a highly complex feature and depends on a multitude of parameters such thickness of the lamination, bending radius, the rate of twist and the lumber species.
Since this stair is highly unique, bending tests of laminations were conducted in our shop to justify a viable product from manufacturing to service. See snapshots of a mock-up jig that aims to determine the prospect of bending and twisting Hem-Fir lumber of various thicknesses.
In addition to the added complexity of manufacturing, the stair spans an unsupported 60ft in a spiral fashion and is susceptible to dynamic excitation, a response due to footfall which tends to govern the design of stairs. Therefore, concrete has been added to limit these dynamic effects and stiffen the overall cross-section through TCC-action while also complicating the design further.
Fabrication
The roof panel trusses of the hub structure at KF Aerospace were fabricated in our shop, each consisting of a DLT top chord, two steel queenposts and a cable. The curvature has been achieved by letting the DLT panels 'sag' over two middle supported jigs, before installing the cable and locking the curvature in place by tensioning the cables.
Also created in StructureCraft's shop were the hangar roof 'rib' trusses, replicated after a plane wing. The glulam top chords are a single piece of glulam, and have been assembled and erected on site with the cable, queenposts and custom designed steel castings to span over 90'.
Installation
DLT roof trusses were curved by arching the panels over two central supports, before locking in the curvature with steel cables and steel queen posts on the ground. All 53 trusses were then craned into place – resulting in an efficient and elegant roof structure – which is also intended to mimic the fuselage of a plane.
The team has completed installing queen posts and cables to the underside of the DLT floor, in order to create an innovative timber-concrete composite truss floor system, to clear span 45’ and to help control deflections and vibrations.
The roof panels over each hangar were then erected, the last major timber component before the curved CLT stair.