Canadian structural engineer, StructureCraft, built a specially crafted, dual-curve timber roof in a long-span format in University of Idaho’s (U of I’s) basketball arena in Moscow, Idaho.
The engineering team behind the project worked to develop, shape, and optimize the curved roof, ensuring its feasibility for fabrication and construction.This meticulous process not only enhanced the architectural vision, but also addressed the various constraints and challenges associated with a doubly curved structure spanning a 5,760-m2 (62,000-sf) arena.
The architect, Opsis Architecture, envisioned the shape of the roof to be inspired by the undulating hilly landscape of the Palouse region, encompassing parts of northern Idaho, southeast Washington State, and some areas of northeast Oregon.
Using timber in a double-curve roof and a structure composed of hybrid timber/steel trusses spanning 36.6 m (120 ft) came with its set of challenges but the structural engineering team at StructureCraft worked in consort with the architect to find a fitting solution. The mass timber, sourced and installed by StructureCraft, featured in this project includes long-span king-post roof trusses, glulam columns, and cross laminated and dowel laminated floors. Consulting firm KPFF provided structural engineering for the building base, and Hoffman Construction Company was the general contractor.
In the arena, thoughtfully designed 3D timber/steel trusses, meticulously proportioned, extend over a length of (45.7 m) 150 ft, reaching a distinctive timber portal frame arch that gracefully delineates the intimate space within the arena. Constructed with locally sourced timber, this newly erected structure has swiftly transformed into a beloved exhibition space, showcasing the university’s pride as well as Idaho’s significant forest industry.
The project primarily utilized locally sourced Glulam, with curved Glulam elements produced by two different manufacturers based in Idaho. This posed a notable challenge since these manufacturers had not previously worked with the precise tolerances required for a project of this magnitude. However, according to StructureCraft, the structural 3D model produced by their team successfully generated all the necessary geometry and shop drawings to produce the unique curved Glulam shapes.
To accomplish this, the engineer’s shop team leveraged its in-house CNC capabilities and employed layout optimization techniques to accurately cut the desired shapes from the actual curved billets received from the Idaho manufacturers. Additionally, the team carefully conducted a “test fit” of each major assembly within the shop to ensure proper fit before shipping the components to the construction site.
To minimize working at a height, the entire portal frame was pre-assembled on site into three components, each weighing over 22,679 kg (50,000 lbs).
The kingpost trusses presented a significant challenge during installation due to their weight and the need for a crane within the bowl. To overcome this obstacle, a parametric model of the trusses was developed using genetic algorithms. This enabled structural optimization while adhering to various aesthetic objectives. As a result, the trusses achieved enhanced structural efficiency, significantly reducing the weights of the prefabricated elements. This approach not only upheld the project’s budget, but also ensured its successful completion.