A timber-concrete composite spiral stair spanning 70′ between two floors of an airplane-shaped museum.

For KF Aerospace‘s Centre for Excellence, our structural engineers proposed a unique design concept: could we connect the two levels of a museum space with a free-standing spiral CLT stair. This posed significant structural challenges; the spiral shape requires the CLT to both bend and warp, and creates forces in a combination of strong and weak axis bending as well as torsion.

The structure is comprised of doubly curved CLT with a concrete topping throughout the full spiral. The addition of the concrete provides the required mass to control vibrations in the 70ft long free span. Creating composite action between the concrete and the CLT significantly increases the overall stiffness of the stair, removing the requirement for any support columns and maintaining a highly aesthetic structure that serves as a welcoming showcase for the Centre.

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