2012 Issue

53 The design intent is to have patrons marvel at the similarity between an actual canyon and this multistory clear space. To achieve the angular appearance of rock, each of the walls has been faceted to provide triangular segments. At the east of the canyon is a concrete wall that is approximately 65 feet tall, fromwhich a cantilever stair goes from the third floor of the South building to the fifth floor of the North building. The tall wall is braced back by baffle walls at about eight feet, zero inches on center (see photo). The intermediate stair landing at the east canyon stairs is surrounded by a concrete feature designed to look like a big boul- der jutting out from the wall. This board- formed, faceted concrete mass cantilevers out from thewall, providing a spectacular vi- sual. The photo below shows the formwork and shoring required to cast this boulder in place. One can see the dowels sticking out from the wall for the cantilever stairs. This wide-open space will allow patrons the opportunity of viewing the canyon floor 40 feet below. The exhibit space in the South building is primarily wide-open, clear-story space. The exhibit architect has designed the space to flow seamlessly with a series of ramps and suspended folding concrete slabs between the levels. The architect wanted to see a maximum thickness of five inches for the folding slabs, which required double-mat reinforcing to satisfy the loading criteria. In the few areas of suspended framing, the floors were designed for heavy exhibit-case racking loads. There are also nonrectangu- lar recesses in the floor framing to accom- modate exhibit displays. There is quite a bit of architecturally ex- posed concrete on this project. Even the structural shear walls are exposed in many cases, showcasing a beautiful board formed finish. Since there was so much exposed, the architect hired a concrete specialist to provide recommendations that met the design objectives. Much consideration was given to things we don’t ordinarily think about as structural engineers, such as color and finish. The desired color of the finished concrete was much lighter than the typical gray, which required the concrete mix to include some atypical ingredients. Lou Nicoletti of Staker and Parson notes, “Slag was im- ported from Illinois and used to substitute some of the Portland cement along with Class F Fly ash (donated by Headwaters Resources) to make the mix brighter and more aesthetically pleasing. The use of three cementitious materials qualifies the self-consolidating concrete mix to be classified as ‘ternary concrete.’ This ternary concrete mix supports the LEED requirement for recycled material using in excess of 65% recycled cementitious material content.” The contractor used self-consolidating concrete at all board-formed locations to achieve the desired look. Self-consolidating concrete is so fluid that they don’t measure slump in vertical inches. Instead, they mea- sure the diameter it spreads to after the cone is lifted. The concrete work is quite exquisite and has presented many con- struction challenges, but the contractor has done an excellent job bringing about the artistic beauty of these structural elements that are normally covered up. Since the museum finds itself perched high upon the hill, it is a very visible proj- ect. The architects have taken great care blending the building into the mountain- side by using colors that complement the natural surroundings. Rio Tinto is a major donor on this project and provided the copper that is used extensively in the skin. Between the copper, the lighter concrete and the metal panels, the colors blend into the surrounding landscape seamlessly. The shape of the North and South soffits also add to the building’s character and attractive appeal. In some cases, 60-foot girder trusses are supported by steel beams cantilevering up to 17 feet from the main column line. The shape of the soffit is achieved using tube steel trusses at six feet on-center to support the cladding. This project has been in our office for a long time now and it is exciting to see it taking shape up on the hill. It has been a privilege to be associated with something so world- class. We were able to rub shoulders with some very talented designers and learn a lot through the process. Our hope is that this museum provides enjoyment and an imaginative thinking outlet for our genera- tion and those that follow.  Rendering Courtesy of Polshek Partnership