Benaroya Hall tops the competition for concrete construction
Not only did the Benaroya Hall project win the Cast-in-Place category, it was the judges' unanimous pick for the Grand Award.
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Benaroya Hall
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Concrete was a vital element in the construction of Seattle Symphony's new home because of the project's noisy location - it is surrounded by busy city streets and an underground railroad tunnel directly below. To top that off, Metro's bus tunnel runs the full length of one of the property lines.
Concrete provided a relatively inexpensive mass to help deaden exterior vibrations. It also allowed seamless structural forms, flexibility of shape, variety in framing systems and speed of construction.
Some of the specifics of the project include:
Concrete foundation mat. The 6-foot-thick mat runs diagonally from one corner of the site to the other, directly over the train tunnel. It carries the weight of the building above without adding load to the tunnel. It also dampens and reflects noise and vibrations from train traffic. Each side of the mat is supported on 6-foot-diameter, cast-in-place concrete piers. The top of the mat serves as the floor for the lowest level of the hall's parking garage.
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Benaroya Hall Auditorium.
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Concrete framing considerations. While the foundation mat provided acoustical coverage over the tunnel, an inexpensive solution also was needed to provide mass throughout the rest of the basement level. The answer was to cast a non-structural, 1-foot-thick lean concrete slab under a 6-inch-thick slab on grade. Lean concrete provided acoustical isolation properties similar to structural concrete at a lower cost. An added benefit of using that approach was a clean working surface for the contractors during the rainy winter.
Concrete parking structure. Two underground parking levels are framed with cast-in-place concrete beams and slabs, then topped with a concrete "lid" - which is nearly twice the weight of the concrete in the slabs, for acoustical and design reasons. To save time and money on the lid, garage formwork was reused and floor-beam depth increased about the slab level.
Concrete transfer beam grid. Continuing the column spacing down from the auditorium would have interfered with an efficient parking layout. The solution is a shallow concrete column transfer system that reduces the necessary garage area by 20 percent, meeting parking goals and avoiding an increase in building height.
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Benaroya Hall's auditorium - a box within a box.
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Concrete auditorium. The cast-in-place concrete auditorium is designed as a "box in a box," with the inner box of the auditorium cradled in the outer box of the surrounding structure. The only connection between the two boxes are 532 rubber isolator bearings at the base. The ability of concrete to be molded into many different shapes and forms allowed for the construction of oddly shaped girders, lugs and surfaces for bearing placement.
Tessellation. Interior auditorium walls are seamless, but unusually shaped. The art of tessellation - the search for repetitive, interlocking shapes - was used to develop the irregular acoustical wall surfaces that was cast using just two sets of forms. The walls provide a massive acoustic substrate for the auditorium's wood paneling. They were precast with tight tolerances, since wood shims could not be used due to acoustical reasons.
Using concrete for Benaroya Hall helped it achieve better than expected acoustical results. Only .3 percent of sound energy enters the auditorium from outside the hall.
The project team included: City of Seattle, owner/developer; Skilling Ward Magnusson Barkshire, structural engineer; Baugh Construction, general contractor; LMN, architect; Baugh and Lease Crutcher Lewis, concrete contractors; and Stoneway Concrete, ready mixed supplier.
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