Building Vibration Isolation for Noise Control
A natural extension of the work on FST vibration isolation was to apply the same design ideas and materials to the isolation of buildings from ground-borne or structure-borne vibration and noise. In the period from 1955 to about 1990, most consultants in the United States believed that lead-asbestos pads were the best available structural isolation material. Many buildings in the Eastern United States were isolated on lead-asbestos pads even though performance was limited. During this period, there were multiple examples of buildings isolated on rubber pads in the United Kingdom, which Dr. Wilson concluded provided a much better isolation design. Dr. Wilson began using natural rubber support bearing pads for building isolation in the 1980s. Early projects included the Birmingham Concert Hall (1980) and the Burnham Plaza Theater (1986), both of which were successfully isolated from ground-borne noise produced by adjacent rail systems.
The first major U.S. concert hall isolation design project for Wilson Ihrig was Benaroya Hall in Seattle, with design starting in 1994 and opening in 1998. The ideal site for Benaroya was in Downtown Seattle near the Seattle Art Museum and Pike Place Market, however the site was directly over a freight and passenger train tunnel and directly adjacent to a bus and light rail tunnel. The site was initially considered unacceptable by the hall acoustician, Dr. Cyril Harris, but his mind was changed when Dr. Wilson determined that a two-stage isolation system could be designed to reduce ground-borne noise from trains to levels below the threshold of hearing with the air conditioning turned off. This project was the first completely vibration isolated performance hall in the United States.
The first stage of the Benaroya Hall isolation system was a very heavy mass foundation built to decrease transmission of the noise and vibration from the ground to the main building, as opposed to a normal mass foundation. The second stage was the performance hall’s box-in-box structure within the main building structure. The performance hall is supported by 7-inch thick natural rubber pads to further reduce noise and vibration from trains in the tunnel below. A unique feature of the isolation system design was that the resilient support pad arrangement included lateral restraint pads of the same thickness as the gravity load support pads to provide the same degree of noise and vibration reduction. The lateral pads were pre-compressed and sized tosupport lateral loads in any direction from an earthquake of up to 0.75 g. This was completely different from most isolation designs which provided only lateral restraint buffers or bumpers: an arrangement that does not maintain the isolation or protect the isolated structure from damage due to seismic events.
With the success of the building isolation configurations and details developed by Dr. Wilson on the Benaroya Hall project, those innovations have been incorporated in the design of 14 other performance halls to reduce ground-borne noise and vibration from trains and other noise and vibration sources. Thousands of people now live and work near rail lines without having excessive levels of noise, ground-borne noise, or perceptible vibration and can enjoy the quietest passages of symphonic music without the distraction of a passing train.