California College of the Arts Expansion

This innovative project blends sustainability with seismic resilience, highlighting the natural beauty and structural functionality of mass timber. Conceived as a creative ecosystem where different art and design disciplines can interact and overlap, the California College of the Arts Expansion establishes a vibrant indoor-outdoor environment for learning and making that strengthens relationships among people, ideas, and creative practices. 
 
The building’s concrete ground level is a hub of indoor-outdoor workshops for more physically intensive art-making practices and fabrication. Emerging from this base, two mass timber pavilions house classrooms, art studios, and exhibition galleries. Leading onto a green-terraced landscape that unites the building’s lower and upper levels, the three-story Hooper Pavilion and one-story Irwin Pavilion are among the first exposed mass timber structures in California. 
 
With their expressive features, the pavilions showcase innovative structural design as well as the ambitious sustainability goals upheld by the California College of the Arts. The Type V-B structures incorporate glulam columns and beams, CLT floor and roof panels, and structural steel, optimizing the distinctive strengths of each material. The exterior of each pavilion is wrapped in a striking timber-steel hybrid eccentrically braced frame (EBF), which combines the stiffness of a concentrically braced frame with the ductility of a moment frame for use in high-seismic zones.  
 
The EBFs were formed using 12-inch-square glulam members, ebony-stained to match the steel. Each was attached to a knife plate using steel dowels, and the plates connect with a single pin to the horizontal perimeter beams wrapping the buildings. Engineers designed the pins so the timber members are only subjected to axial loads, simplifying the connection by providing rotational freedom.  
 
To meet San Francisco’s challenging seismic requirements, engineers decoupled the gravity and lateral systems. The mass timber gravity systems—3-ply CLT panels with glulam beams, girders, and columns—were carefully detailed with consideration for lateral seismic drift. The EBF lateral systems are slightly offset from the gravity structures and wrapped around the building perimeters, adding robustness and ductility. In addition, seated glulam beam and column base connections were designed with slotted holes to avoid inhibiting the rotations of the members, which could happen with lateral building displacement. Because CLT diaphragms were not prescriptively recognized in the code at the time the project was permitted, concrete floor toppings are used as the diaphragms and are tied to the horizontal perimeter beams. This groundbreaking seismic design underwent a rigorous peer review to validate the approach. 
 
The glulam was preservative pressure treated in accordance with American Wood Protection Association (AWPA) Use Category 3B (UC3B), intended for exterior applications where the wood is not in direct contact with the ground. Dowels and fasteners were installed only from the inside of the building, avoiding exposed holes on the exterior. The braced frames were also fabricated with drip edges at the ends, and a saw cut for the connecting knife plate was added to the underside of each brace to prevent water from becoming trapped.