Structural design for vibration isolation at Benaroya Hall

Abstract

Vibration and noise isolation criteria, together with an urban site for the Seattle Symphony Hall, created unusual constraints for its structural design. A massive concrete mat foundation bridges and isolates the railroad tunnel running diagonally under the site. Two garage levels and an isolation level further separate the Auditorium from the tunnel, while 30 ft of unexcavated soil remain between the Auditorium and an adjacent underground transit station. Heavy concrete construction is used extensively to add mass for isolation. Concrete topping was added to the Auditorium roof for isolation, and double concrete walls surround the Auditorium. Exterior precast concrete cladding adds further mass and isolation. To speed construction time, the Auditorium balconies, including the inner walls which were cast to odd geometric shapes, are precast concrete. The Auditorium structure is isolated from the surrounding structure by an uninterrupted, 7-in.-wide joint, creating a ‘‘box within a box’’ The only structural connections to the Auditorium inner box are two types of special, natural rubber isolation bearings at its base. One bearing type takes gravity loads. The other type, initially prestressed, takes lateral loads. The need for bearing access under the base of the Auditorium created unusually shaped transfer girders.