- 45,000 square foot addition on restricted urban site
- “Box-within-a-box” construction acoustically isolates theater
- Auger-cast pile foundations reduce vibration and noise
- Vierendeel trusses
- Continued performance function during construction
The Children’s Theatre expansion adds 45,000 square feet to the original Kenzo Tang structure, which was part of the 1974 expansion of the adjacent Minneapolis Institute of Arts. Built on a significantly restricted site the expansion adds another smaller theater, an education center with classrooms, and expanded prop shops and storage.
Because the site is located in a dense urban neighborhood and directly flanked by the Minneapolis Institute of Arts, there was little room for lateral expansion, so one of the solutions for placing the addition had to include efficient use of vertical space within the new site plan. Structurally, this meant adding a below grade level. To achieve the programming requirements of this space, a unique system of concrete struts and post-tensioned concrete ties was used to shunt loads away from the existing adjacent foundation wall and ensure overall stability of the structure. The system also helped meet the challenge of providing column-free spaces in the above theater, rehearsal, hall, and dance studio.
To prevent noise and vibration from adjacent spaces disturbing activity in the new 300-person capacity theater, MBJ designed a “box-within-a box,” which involved surrounding the theater (the inner box) with a 3-inch buffer of air (the outer box). The theater floor is composed of a 4-inch concrete slab supported on high capacity neoprene bearing pads. The pads elevate the floor slab 3 inches above the wide-module pan-and-joist concrete first floor system. The theater’s perimeter is composed of upturned concrete curbs that support 45 foot tall load-bearing concrete masonry-unit walls. The result is a space in which actors’ voices and production sounds are undisturbed by outside noise. Another special structural feature of the theater is two structural steel Vierendeel trusses at the theater’s roof. The trusses support a system of structural steel purlins, trolley beams, and pipe hangers, from which a lower catwalk and removable grid system of rigging and lighting spanning the entire width of the theater are suspended.
MBJ used auger cast piles, which extend to bedrock, thereby increasing the allowable soil bearing capacity in comparison to the existing building. Columns, piling, and unusually sized pile caps were meticulously designed and located between existing footings of the building and coordinated with the programming spaces of the four floors above. One of the results is a building with very few columns given the square footage of the typical floor. Piling also helped limit the potential for differential vertical settlement between the existing building and the new addition. The auger-cast piles, while slightly higher in cost, allowed the existing theatre to remain open and continue to generate revenue as well as provide the owner lower maintenance costs typically associated with problems involving differential settlement.