KF Aerospace Centre for Excellence
The new KF Aerospace Centre for Excellence is coming to Kelowna! We are excited to be working 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, wishes to create a project 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 will house historical planes. The building showcases the latest in structural innovation and mass timber construction throughout the superstructure. From wing-shaped hangar roofs to a world-first doubly-curved CLT staircase, a creative approach to structural engineering is 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 has been busy scheming efficient and elegant solutions for the different building components.
Stay tuned for project updates! Grand opening in 2022.
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 will be sourced and manufactured from within BC.
For the two aircraft hangar “wings”, our structural engineering team has been working hard on answering the question: How do we create one of most efficient “wing” building structures worldwide? Taking queue from the aerospace industry, we are using the latest in computational design techniques to optimize structural solutions for these unique roof structures.
The long spans of the hangar roofs present 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.
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 instead of the jigs and four people each end.
Curved CLT Stair Laminations Test
Timber composite concrete (TCC) elements is a well-known structural element that keeps evolving. Cross-laminated timber (CLT) is a well-know timber product commonly used as 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. 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 added twisting of 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 and, to our knowledge, the first of its kind in the world, bending tests of laminations are being 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.
The roof panel trusses of the hub structure at KF Aerospace are currently in fabrication, each consisting of a DLT top chord, two steel queenposts and a cable. The curvature is being 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 being created in StructureCraft's shop are the hangar roof 'rib' trusses, replicated after a plane wing. The glulam top chords are a single piece of glulam, and will be assembled on site with the cable, queenposts and custom designed steel castings to span over 90'.
The CLT wall panels, large steel trusses which span over the hangar doors, and glulam purlin and plywood roof panels to cover the hangar roofs are also being fabricated currently.