To view the figures and tables associated with this article, please refer to the flipbook above.
Nestled among the redwoods on forested acreage marked by the ridges and ravines inherent to Northern California, the University of California, Santa Cruz’s (UCSC’s) new Kresge College Academic Center features a unique approach to hybrid design and construction different from the typical “steel-beams-and-timber-slab” hybrid model. The largest of the 125,000-square-foot expansion’s four buildings, the Center’s below-grade concrete podium and retaining walls hold back the hillside, supporting an impressive “lobed” mass timber roof that celebrates the inherent beauty of exposed wood. Light-frame wooden shear walls and a steel moment frame round out the design as the primary lateral system of the roof structure. The Center’s Cross-Laminated Timber (CLT) diaphragm is pushing the limits beyond what was formally codified at the time of design. Working collaboratively with the design architect and contractor, Magnusson Klemencic Associates (MKA) created a structural design that bridged the gap between vision and reality, historic and modern, and mass timber and hybrid systems.
‘Curvature and Porosity’
Design architect and architect of record Studio Gang envisioned Kresge’s four-building expansion—the Kresge College Academic Center and a trio of mass timber residence halls—as an opportunity to increase the College’s accessibility and better connect it with the surrounding natural ecology and the greater UCSC campus. The new buildings do not replicate the original campus buildings designed by Charles Moore and William Turnbull in 1973, but rather “engage it in a dialogue that complements its rectilinear, angular language with a more organic one of curvature and porosity,” as described by Studio Gang.
The selection of wood was prioritized for sustainability, as wood construction produces less carbon emissions than steel or concrete, a critical driver for Studio Gang.
The eight-acre expansion site is small and features a steep, uneven hillside drop-off to the east, above which the Kresge College Academic Center is perched. All the new buildings were sited and designed to minimize the removal of redwood trees to preserve the natural environment whenever possible, resulting in the building’s asymmetrical pod-like form inspired by the growth patterns of polypore fungi.
The Kresge College Academic Center includes four wings, or lobes, containing office, classroom, and lecture spaces connected to a large 600-seat lecture hall to the north at the primary upper-grade entry level. Here, the structural slab is lowered to accommodate a raised access floor. The raised floor provides a mechanical plenum and forms the tiered platforms and steps in the lecture hall and classrooms. The center of the building contains a triple-height atrium that shows off a curved, architectural concrete retaining wall and slender cast-in-place stairs that bring occupants down to the two lower levels, which terrace down, following the steep slope of the site.
Choosing the Right Material
While a concrete podium and retaining wall structure made sense for a large building built into the hillside above a ravine, UCSC chose exposed mass timber for the Center’s roof structure, where it could be most celebrated. The roof framing above the ground floor level consists of three- and five-ply CLT slabs spanning between glued-laminated timber (glulam) beams. Within the lobes of the building, glulam beams, ranging from 21–31½ inches deep, are gently curved upward to follow the geometry of the roof and rest on slender perimeter glulam columns designed to maximize window views. The CLT panels within the lobes are faceted to follow the curvature of the roof. This system provides flexibility for the variety of programs within each lobe, delivers an appealing exposed timber aesthetic, and maximizes views to the outside.
MKA utilized a light-frame wood shear wall lateral system and a single-bay steel moment frame to support the mass timber roof. The steel moment frame was selected to provide a 40-foot clear span at the south end of the large lecture hall, a critical aspect of the architectural vision, while efficiently integrating with the mass timber framing. The Center also utilizes a CLT diaphragm to distribute seismic loads to the shear walls and moment frame. MKA collaborated with WoodWorks on this unique diaphragm approach, which was vetted by a peer review process and ultimately resulted in cost savings by eliminating plywood sheathing and steel strapping.
Terracing down the steep grade of the site, a concrete podium was chosen for the lower two levels of the Kresge College Academic Center for its strength, stiffness, and durability. Concrete walls up to 18 inches thick and two stories tall support significant unbalanced permanent soil load. Below-grade slabs up to 12 inches thick were chosen based on compatibility with the retaining wall and the need to cantilever up to 15 feet at the atrium while minimizing structural depth. Concrete podium shear walls support the seismic and unbalanced soil load for strength and stiffness. The foundation system combines isolated spread footings and combined mat foundations. The mat foundations were used to incorporate the building’s complex geometry (in plan and elevation) while minimizing the volume of concrete required.
The juxtaposition between the smooth, exposed concrete of the lower levels and the mass timber above met the architectural vision of embracing the natural ecology of the site without losing the practicality and strength of a concrete-supported structure.
Naturally Unique
In this timber project, the building’s beams, walls, and roof subtly curve to reflect the natural environment and provide complementary contrast to the College’s earlier architecture. Large windows throughout the lecture spaces let in natural light.
Construction of the Kresge College Academic Center began in 2020, and the building opened to students in 2023.
The Kresge College Academic Center is a unique approach to hybrid construction, recognizing opportunities to use materials and systems in less conventional ways to benefit the project. By remaining open to all materials during the early stages of design, MKA and the project team were able to integrate them in ways that play to each material’s inherent strengths and push their limits. Materials might make sense where they are least expected.
About the Authors
Alex Wilson, PE, is a Senior Design Engineer at Magnusson Klemencic Associates (MKA).
Ian McFarlane, PE, SE, is a Senior Principal at MKA.