Track 1: DOCUMENTATION AND DIAGNOSTICS – UNDERSTANDING HISTORIC PLACES / Volet 1 : Documentation et diagnostic – Comprendre les lieux historiques

West Block Pendulums: Mackenzie Tower and the use of early engineering technology

Friday, October 13
3:00 PM - 4:30 PM

During the late 20th century, with the construction of taller and taller buildings, engineers developed tuned mass dampers and other advanced approaches to stabilize towers against excessive motion caused by external forces such as high winds, hurricanes/typhoons, and seismic events. The earliest use of tuned mass dampers in the U.S. began with the construction of Citicorp Center in New York City, a 59-storey tower built in 1977. But does this mark when architects and engineers began to use engineered controls to counteract external forces of nature?

West Block, one of the three buildings on Parliament Hill, possesses an unusual feature that up until the current rehabilitation project hung in obscurity since it’s construction in 1878. Near the top of Mackenzie Tower are two pendulums suspended inside of each of the masonry spires. They were incorporated into the original construction to prevent excessive movement in high winds and provide flexibility.

During the course of the masonry rehabilitation work, various team members felt that the pendulums were a unique feature, certainly in Ottawa, and possibly in Canada or even farther afield. But are they? Are pendulums exceptional or were they commonly used, and we are simply no longer familiar with them? Initial research reveals that pendulums have been in use as an engineered control since the 18th century devised by Sir Christopher Wren, and even earlier to the 7th century with the use of shock-absorbing shinbashira in Japanese pagodas.

This presentation will explore the early use of counterweights to stabilize tall slender structures and how they became to be incorporated into tower and spire designs. We will look at a few examples of the early use of counterweights, and I will then present the Mackenzie Tower pendulums, explaining their construction and detailing, and the decision to retain them during the recent masonry rehabilitation work.

Learning Objectives:

Caroline Guay

Senior Conservation Technologist
Heritage Conservation Services / PSPC

Caroline has over thirty years' experience working as a Senior Conservation Technologist in both the private and public sector. She has a strong background in the investigation and assessment of building conditions, advising on material conservation issues, and project management and oversight related to cultural assets. In 2016, she returned to the federal government after spending three years working on the masonry conservation team retained by the construction manager.


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West Block Pendulums: Mackenzie Tower and the use of early engineering technology

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