Colby College Athletic Complex: Winner of an ACEC/MA 2022 Silver Engineering Excellence Award

In 2020, Colby College opened the doors of their new state-of-the-art Harold Alfond Athletics and Recreation Center. The 354,000ft² building transcends conventional athletics and recreation center design, efficiently and elegantly integrating all of Colby's indoor competition venues, training areas, and ancillary spaces to comprehensively serve every athletics and recreation program on campus. 

Under one roof, the project contains:

• The only Olympic-sized Myrtha pool in Maine
• A dedicated ice area providing year-round ice
• A gym with three regulation basketball courts
• A track and field oval including a running track with accommodations for field events
• An indoor rock climbing and bouldering wall
• A squash center with nine championship regulation courts
• A three-level fitness center
• Athletic administration offices, classroom, and locker room spaces

London-based Hopkins Architects, served as executive architect, and Sasaki was the Architect of Record. Arup provided the full suite of engineering and consulting services for the project, including structural, mechanical, electrical, plumbing, and fire protection engineering, as well as acoustics, audio visual, facades, IT/communications, security, and sustainability consulting.
 
The building has received LEED Platinum certification — almost unheard of in large-scale sports facility design. The Hopkins-Sasaki team and Arup reviewed every assumption and took every opportunity to seek out ways to optimize resources, minimize embodied carbon, reduce energy and water use, and reduce carbon and greenhouse gas emissions. The combination of solutions developed by Arup – which include daylight harvesting, air system energy recovery wheels, and a pool heating system powered by excess waste heat – enabled the team to reduce energy use to 47% below the modern code baseline. 

Structural System
Structural steel is used for the primary gravity system (columns, suspended floors, and roofs) as well as the lateral system (concentric braced frames). Individual shallow spread footings are provided under columns, and the lowest level floors are reinforced concrete slabs on grade. 

Due to the large size of the building, movement joints were used to divide the larger volumes into separate structural systems. The project was divided into six structurally separate buildings: field house, gymnasium, ice arena, aquatics center, squash center, and central spaces. The roof and façade systems are designed with flexible detailing to accommodate the resulting movements, and double columns are provided along movement joints where required.

Figure 1: Project Division 
 

Conventional Construction

Two of the six buildings (squash center and central building) are conventional steel suspended floor and roof framing of steel wide flange beams supporting composite lightweight slab on metal deck. The ground floor is a slab on grade.

Lateral stability of the buildings is provided by concentric steel braced frames. Columns are wide flanged rolled steel sections and the braces are circular hollow structural sections, with bolted gusset plate connections. 

Long Span Roof Systems
The other four of the six buildings (field house, gymnasium, ice arena, and aquatics center) employ variations on a similar long span roof design. The steel trusses were a primary component of the architectural design of the space, and details were developed to provide a common architectural expression while being flexible enough to provide structural efficiency in the various geometries and spans of the venues. The spans varied from 130' up to 200', and the shape of each truss was determined by both the required horizontal span, as well as the required vertical clearances above the sporting surfaces. These vertical clearances varied based on the competition requirements of each space, and the bottom chords were curved in a single arc which simplified fabrication while also maximizing depth.
 
The long span roofs are supported by a series of portal frames with truss construction on thirty-foot centers. The truss chords are rolled wide flange sections with bolted joints. The perimeter elements are wide flange sections, with the bottom chord as a curved member of constant radius. The internal verticals and diagonals are back-to-back channels bolted to gussets plates. Full capacity bolted splices were provided as required such that segments of the portal truss did not exceed 70 feet in length. These limits were considered to avoid trucking complications in transporting the steel from the fabrication plant in Canada to the site in Maine. 

To improve steel efficiency and minimize foundation complications, the opposing columns are typically tied at their base by Grade 75 #24 bars encased in concrete to resist imposed thrusting forces. At the aquatic center, the pool physically prevented the horizontal tie approach from being implemented, so special foundations were designed which mobilized concrete weight and soil pressure to resist thrusting forces. At the ice arena, the workpoint of the trusses was dropped deeper than typical to allow the ties to pass under the ice.

Secondary framing spanning perpendicular to the trusses is provided by steel open web joists with acoustical metal roof deck spanning between them. Lateral stability of the buildings is provided by concentric steel braced frames. Columns are wide flanged rolled steel sections and the braces are exposed circular hollow structural sections, with bolted gusset plate connections.

 Figure 2: Schematic Sketch of Typical Portal Truss

Figure 3: Completed Portal Truss in Aquatics Center

Loading Considerations
Given the large expanse of roof and location of the project in Maine, a site-specific snow report was commissioned from RWDI. The report provided roof snow and drift loading which was specifically tied to the project location and geometry, rather than using the code-specified values. With such a large roof area, the study was undertaken to refine loads as much as possible as part of the project's overall push for minimizing steel weight.

The exposed steel trusses were also evaluated for extraordinary event loading under the possibility of fires within the event spaces. Jensen Hughes provided fire modelling to provide anticipated steel temperatures, which in turn reduced the stiffness of structural members. The trusses were then evaluated for load distribution arising from stiffness redistribution, to ensure that strength and stability was maintained in the event of a large fire. 

The structural optimization cut the project’s overall embodied carbon by an estimated 800t – the equivalent of nearly two million miles driven in an average passenger vehicle!