Idaho Central Credit Union Arena

Moscow, ID, USA · Completed 2021

Project facts

Client: University of Idaho
Architect: Opsis Architecture
Sports Architect: Hastings + Chivetta Architects
General Contractor: Hoffman Construction
Base Building Engineer: KPFF
Size: $51M
Location: Moscow, ID, USA
Status: Completed 2021
Our involvement: Structural Engineer of Record - Roof
Timber Sourcing, Prefabrication & Installation

Photography & imagery

Completed photography: Lara Swimmer; University of Idaho Creative Services
Diagrams / renders: StructureCraft

Long-Span Timber Sports Arena

The University of Idaho basketball arena models the use of timber in long-span sports facilities in North America. The 4,200-seat arena is the new home for the Vandals’ varsity basketball teams and a gathering place for a variety of school and community events.

The University engaged StructureCraft as structural engineer of record and builder for the innovative doubly curved timber roof. Carefully proportioned 3D timber/steel trusses span 150ft to a unique timber proscenium arch, elegantly defining the intimate arena space. Using local timber, the new structure has quickly become a dearly loved showcase for both the University and Idaho’s important forest industry.

Completed view of Idaho Central Credit Union Arena

Interior view of Idaho Central Credit Union Arena

Design

The roof is a doubly curved plywood diaphragm supported by hybrid timber/steel trusses, carefully proportioned for both aesthetics and structural efficiency. The engineering team with the architect developed, shaped and optimized the curved roof for fabrication and constructability, enhancing the architectural vision, while meeting the numerous constraints and challenges associated with a doubly curved structure.

One of the many unique features of this project is the efficient timber/steel portal frame that spans 120’ to allow for viewing from the secondary seating at the practice rink. Complex timber engineering was required to design the thrust connection between beam and column to transfer over 450,000 lbs. of compression.

Elevation drawing for Idaho Central Credit Union Arena

Crowded arena beneath an exposed timber roof at Idaho Central Credit Union Arena

Three-dimensional structural model of Idaho Central Credit Union Arena

Steel connection diagram for Idaho Central Credit Union Arena

Fabrication

Local Glulam was used for most of the project, and two different manufacturers in Idaho produced the curved Glulam. This was a significant challenge, as they had not previously worked with the tolerances required for this scale of project. Our structural 3D model produced all the geometry and shop drawings required to produce the curved Glulam shapes, each of which had a unique curvature.

Our skilled shop team used in-house CNC capabilities along with layout optimization to cut the desired shapes out of the actual curved billets we received from the Idaho manufacturers. We also “test fit” each of the major assemblies in our shop, ensuring fit prior to shipping the components to site.

Curved arena beam assembly in the fabrication shop

Components for Idaho Central Credit Union Arena during shop fabrication

Curved arena beam segments in the fabrication shop

Installation

The entire portal frame was pre-assembled on site into three large components weighing over 50,000 lb. to minimize work at height.

The kingpost trusses span over 150 ft. across the main arena. One of the key challenges was installation of these heavy elements with a crane in the bowl. A parametric model of the trusses was created using genetic algorithms to perform a structural optimization on the trusses, while respecting numerous aesthetic objectives. This created structural efficiency and, importantly, reduced weights of the prefabricated pieces. This also allowed the project budget to be maintained.