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An iconic work of art is now complete in the heart of downtown Tampa, Fla., after more than a decade of efforts to replace its predecessor. The new Tampa Museum of Art replaces a 1979 facility that has been plagued with numerous criticisms throughout most of its existence including inadequate size, functionality, and presence in the community. In 2006, the museum board and the City of Tampa agreed to use public and private funds to construct a new $33 million, 66,000-square-foot museum in the redesigned Curtis Hixon Waterfront Park as part of the Riverwalk project along the scenic banks of the Hillsborough River. Known for using clean lines and practical materials in his buildings, architect Stanley Saitowitz, based in San Francisco, was chosen as the project designer. Museum criticisms of the past are now a distant memory for the City of Tampa because the new Tampa Museum of Art is an engineered work of art.
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The design
With the adjacent river located close to sea level, the museum’s primary requirement for programmed space was to ensure all art work, whether on display or in storage, be kept above the 18-foot flood plain. The architect embraced the opportunity to elevate the art by developing his vision of a “jewel box” hovering over a plinth of glass recessed beneath it. The illusion is achieved with massive cantilevers that thrust the second and third stories over the museum’s first floor outdoor promenades. It’s an innovative solution for a practical problem: providing shaded terrace areas as well as adding more usable space to the building’s footprint. The museum’s long mass is split in right down the middle. A three-level museum-support space is located on the east half and consists of offices, conference rooms, storage, security, receiving, and a “flying balcony” overlooking Tampa’s skyline. A two-level public space is located on the west half and consists of a lobby, conference rooms, restaurant, souvenir store, grand stair case, double-story exhibit space, and a balcony overlooking the river and the spectacular Florida sunsets.
The new Tampa Museum of Art replaces a 1979 facility that has been plagued with numerous criticisms throughout most of its existence including inadequate size, functionality, and presence in the community.
The Tampa Museum of Art was crafted by Walter P Moore’s Dylan S. Richard, P.E., and Richard J.A. Temple, P.E.
With the four corners of the “jewel box” hovering approximately 18 feet above the ground level plaza, the team designed a matrix of two-way truss framing to support both the east and west faces of the building.
With the adjacent river located close to sea level, the museum’s primary requirement for programmed space was to ensure all art work, whether on display or in storage, be kept above the 18-foot flood plain..
The museum is home to a variety of contemporary pieces.
Known for using clean lines and practical materials in his buildings, architect Stanley Saitowitz, based in San Francisco, was chosen as the project designer.
An expanse of metal consisting of 90,000 square feet of 1/8-inch perforated anodized aluminum panels wraps the building.
Museum criticisms of the past are now a distant memory for the City of Tampa because the new Tampa Museum of Art is an engineered work of art.
At the Grand Opening on February 4, 2010, Saitowitz stated, "This museum is both timeless and of our time, an electronic jewel box, floating on a glass pedestal, a billboard to the future, and a container to house works inspired with vision and able to show us other ways to see our world. The museum hovers in the park, a hyphen between ground and sky."
The structure
The Tampa Museum of Art is composed of a structural steel frame connected to three cast-in-place concrete elevator/stair towers along the north face of the building. The frame extends beyond the supports by 40 feet, including the 20-foot-cantilevered floors on the east and west faces. To the south, the elevated floors cantilever by 40 feet. The structural design team made the iconic cantilevers a reality by introducing a series of diagonal wide flange steel braces to create two-story trusses in the museum’s support space and a series of 11-foot-tall wide flange steel trusses at the roof level from which the public art galleries hang; see the BIM model in Figures 1 and 2. The two-way trusses laced within the traditional steel beam and column frame provide the stiffness required for both strength and serviceability of the cantilevers. The floor systems are composed of 4-1/2 inch normal weight concrete on 3-inch composite steel deck supported by structural steel composite beams. All public spaces in the building were designed with 3-inch white concrete topping slabs that serve as the finished floor surface. Each white concrete topping slab is polished and contains a series of saw-cut control joints to resist shrinkage cracking in the finished concrete floor surface. The control joints align architecturally with matching lines in the curtain wall system at grade as well as align with the ceilings in exhibit spaces. The roof system consists of 3-inch steel roof deck supported by structural steel beams.
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The cantilevered structural steel frame’s continuous overturning forces are resisted by numerous axial steel connections that ultimately tie to the cast-in-place concrete elevator/stair towers. The three elevator/stair towers were identified early in design as ideal cast-in-place concrete shafts to serve as the housing for the building’s vertical circulation and as the structure’s “anchors” for lateral stability against overturning and hurricane force winds. Each tower measures 12 feet wide by 31 feet long with the long direction oriented north/south (in the direction of the 40-foot-long cantilevers) to optimize their overturning capacities. Use of the elevator/stair towers for lateral stability also enabled the design team to eliminate all steel braces from the first elevated floor down to the foundation system, yielding a brace-free ground floor.
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A drilled-shaft deep foundation system was used to support the museum structure with 31 48-inch-diameter and nine 60-inch-diameter drilled-shafts; depths ranged from 45 feet to 60 feet. The drilled shafts were installed into a limestone layer roughly 40 feet below the existing grade with embedments ranging from 5 feet to 20 feet deep. These deep foundations relied primarily on skin friction in the limestone for resistance of gravity loads and cantilever action of the drilled-shafts above the limestone layer embedment to resist lateral loads.
The engineering
Flatness of the cantilevered floors was critical. The most significant challenge the design team faced was to ensure that the cantilevered portions of the building were perfectly flat when completed. Based on early reviews of the structural analysis and BIM models, the design team realized that the sequence of construction for the structural steel frame was not only crucial to attaining final floor elevations, but that the structural frame had to be analyzed and designed to accommodate each step of the sequence. Structural engineers developed and specified an erection procedure that utilized temporary erection post shores under each end of the cantilevered trusses. This allowed the contractor to erect the structural steel frame in a more traditional sequence. The top elevation of each temporary erection column was identified in the contract documents to account for the amount of calculated deflection at each cantilevered end due to initial settlement of the steel frame and the subsequent addition of building dead loads after the temporary erection shores were removed. A “cambered” elevation of the cantilevers at the 13 temporary erection post shores was specified ranging between 1/2 inch and 1-7/8 inch. The contractor followed the design team’s erection sequence exactly, which resulted in final cantilevered floor framing elevations that only varied ±1/4 inch from the design floor elevation at any location along the building’s 550 linear feet of cantilevered perimeter.
With the four corners of the “jewel box” hovering approximately 18 feet above the ground level plaza, we designed a matrix of two-way truss framing to support both the east and west faces of the building. Trusses located in the east-west direction along the two center column grids of the building provide support for three-span north-south trusses cantilevered to the building corners. The number of analysis iterations in these areas was significantly increased from that of a more traditional, non-cantilevered structure because of multiple dead and live load combinations required both for the construction sequence and for the completed structure.
The cantilevered structural steel frame requires between 60 and 410 kips of continuous resistance at each of the connections to the elevator/stair tower “anchors” just to stabilize the buildings gravity loads. The challenge of distributing these continuous tensile forces into the concrete shearwalls was solved with a series of 1-inch-thick by 15-inches-wide by 18-1/2-foot-long embed plates — each containing 36 headed-stud-anchors — centered on its respective shearwall. Breakout for each of these roughly 1,000 pound embed-plates is resisted by an array of carefully detailed hairpin and crosstie reinforcing.
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The grand stair — The museum’s grand staircase hovers above the main lobby floor. A thin and light structure with white precast concrete treads and glass handrails is framed with minimal steel for support. A single HSS14x10 stringer spanning from grade to an intermediate landing HSS steel column to the second level framing supports a 4-inch thick precast concrete landing and 4-inch thick precast concrete treads centered on and cantilevered off each side of their support. The primary challenge of the grand staircase was providing a design that met the architect’s vision of a dramatic stair that reaches up to the art on the floors above while controlling the stair’s natural vibration frequencies. The final grand staircase design is a precise blend of structure and architecture that serves as the centerpiece of the museum’s 55-foot-tall main lobby.
The exterior — The exterior cladding of the Tampa Museum of Art creates the “jewel box.” An expanse of metal consisting of 90,000 square feet of 1/8-inch perforated anodized aluminum panels wraps the building. With one layer of panels on the north face and two layers of panels on the south, east, and west faces, the “jewel box” contains more than 800,000 3-inch diameter holes spaced 4-inches apart in each direction. By day, the metal sheathing shines in the Florida sun, and by night the south façade is illuminated by an LED light exhibit that glows between the two layers and radiates through the array of perforations, creating streams of light through each of the holes. The façade’s challenge was not so much structural or design, but rather the installation. The contractor and sub-contractors spent many days preparing, measuring, and installing each 8-foot by 4-foot aluminum panel to create a 300-foot by 125-foot by 40-foot box, with precisely leveled, plumbed, and squared edges at each corner. But the results give the exterior of the museum an artistic feel that complements what it holds inside.
An engineered work of art
The Tampa Museum of Art is a testament to Stanley Saitowitz’s vision, Walter P Moore’s structural design, Skanska USA’s construction, and most importantly to the Tampa Bay community’s determination. When the structural frame was completed and the erection towers removed, Tampa Museum of Art Director Todd Smith, in his quarterly newsletter, encouraged the Tampa Bay community to “witness a significant milestone and see pure unadulterated genius in concrete and steel.” At the Grand Opening on February 4, 2010, Saitowitz stated, “This museum is both timeless and of our time, a billboard to the future, and a container to house works inspired with vision and able to show us other ways to see our world. The museum hovers in the park, a hyphen between ground and sky.” The new world-class Tampa Museum of Art is an engineered work of art.
Spotlight: Walter P Moore Q&A with the structural engineer JG: What types of structural systems did your team evaluate for this project, and what did you learn? DR: Because of the building cantilevers, structural steel framing was identified early in the design to be the most feasible structural system for the project. The architect’s design vision was an art museum that would appear to float above a glass box. The challenge was to create an economical cantilevered structure that would accomplish this vision. Through discussions and studies with the construction manager, alternate configurations of two-story deep trusses and single roof level trusses along with cast-in-place concrete shearwalls was reviewed. Cost estimates were prepared for these options with different cantilever lengths. From this the most viable structural scheme to accommodate the architect’s design was selected, and very economical solution was achieved JG: What was the most unique problem to solve on the project? How was it solved? DR: The most unique aspect of the Tampa Museum of Art project was how to erect the multi-directional cantilevers. The design team developed a procedure to temporarily shore the cantilevered structural steel framing with specific camber values (ranging from 1/2 inch to 1-7/8 inch) at each grid line. Once the steel frame was completely assembled and anchored to the shearwalls, a survey was performed to ensure the proper camber values specified on the Contract Documents were provided. The temporary shores were then removed one by one to allow the cantilevers to fully engage and the structure was again surveyed to confirm no excessive deflections had occurred. The final step was to cast the primary structural composite slab followed by a white concrete topping slab (in the gallery space only). The floor system cambers at the cantilever tips all came out to within +/- 1/4 inch from level. JG: To what extent was building information modeling (BIM) used on this project? DR: The Contract Documents were developed from the Revit structural model. A NavisWorks model was created from the Revit model to aide in coordination efforts within the design team and with the construction team. JG: How was BIM used on this project to benefit the whole project team? DR: The NavisWorks model was shared with the entire project team and proved to be a very beneficial to understand the complex structural system and how it needed to be integrated into the overall design of the art galleries and the required construction sequence. JG: What software did the design team use for the project design? DR: Structural analysis was performed in SAP2000, which is developed by Computers & Structures, while design modeling and documents were done in Autodesk’s Revit Structure 2009. JG: What lessons did you learn from this project that you will apply towards future projects? DR: The cladding for the Tampa Museum of Art consists of 75,000 square feet of 1/8 inch perforated anodized aluminum sheets around the perimeter walls and under the cantilevered framing for the appearance of a metal box floating atop an inner ring of glass walls at the ground level. Dimensional precision and deflection serviceability limits were heightened on this project to ensure the perforated aluminum sheet cladding remained flat on every surface and matched perfectly at every corner of the building. The lesson learned from this project was how easily the architect’s vision for the exterior of the building could have been compromised if the design and construction teams had not established and maintained the level of detail that was ultimately provided. Firm Facts |
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By the numbers: Tampa Art Museum
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Dylan S. Richard, P.E., is a principal and was the project manager for the Tampa Museum of Art. Richard J.A. Temple, P.E., is a senior principal and was the engineer-of-record and principal-in-charge for the project. Both are in Walter P Moore’s Tampa, Fla., office and can be reached at drichard@walterpmoore.com and rtemple@walterpmoore.com, respectively.
