Project: Frontier State Bank, Oklahoma City, Oklahoma
Client: Arcways Inc., Neenah, WI
Project Description: Custom Curved Wood Stair
Project Scope: Provide engineering services in the preliminary design phase to aid Arcways in selling a buildable wood stair concept to the owner. Provide final engineering services to design and detail the wood stair.
Project Challenges: The customer chose to have the stair to be constructed of wood. The treads and risers are Select Structural Maple while the stringers are constructed of laminated plywood that has maple overlays. Given the commercial occupancy, the wood stair was designed to support a 100 psf live load. The stair was also designed to have the treads clad in marble as well as art-glass chandeliers hung from the landing members (the marble was not installed in favor of Maple treads). Both the commercial live load and the dead load of the finish materials yielded serviceability issues such as differential deflection between stringers. The concerns were addressed by iterating with varying stiffness of the outside to inside stringers as well as incorporating connections that provided continuity for the outside stringer to help reduce/equalize the displacements under design loads. The use of large rolled steel gusset plates, laminated within the profile of the wood stringers was required to provide the continuity/limit the deflections of the outside stringer. Typical steel gusset plate connections had approximately 40 through bolts to connect the two independent stringer pieces together at landing locations.
Of Note: According to Arcways, they’ve “checked with the Stairway Manufacturers Association and there is nothing on record that remotely comes close to the massive scale of these circular commercial stairs out of wood nationally or internationally.”
