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Making and setting up canopy is a big job

It may look like a simple expanse of white, but the canopy over the platform at Commencement has been the focus of just as much detailed organization as other aspects of the event.

Jerome Milgram, professor of ocean engineering, has produced dozens of computerized plans and blueprints for the design of two different canopies, which are tensile structures supported entirely by tension cables with no posts or columns giving the best appearance and avoiding obstructing the audience's view. The first canopy was created in 1979 when Commencement was first held outdoors in Killian Court; a new one will be used this year because the old one often tore during installation as the material aged because of mechanical stresses and exposure to sunlight. The new canopy measures 5,300 square feet compared to 4,200 square feet for the old one, which did not fully cover the platform. Physical Plant workers installed the canopy on Friday, June 2.

The new canopy's fabric is also different, because the material used in the old one is no longer manufactured in the United States. A preferred canopy fabric has little or no finishing resin in it, as this allows the yarns to slip a bit under load and thereby spread concentrated loads over many of the yarns, in addition to giving the most crease-resistant fabric, Professor Milgram explained.

Fabrics with more finishing resin like that used in the new canopy are more resistant to distortion and are best for sails with stable shapes. The only low-finish fabric that could be obtained in time for the new canopy is the very heavy cloth used to make the sails for square-riggers or "tall ships" that would make the canopy excessively heavy and harder to deal with. Rather than delay the new canopy for a year and seek the best fabric in the interim, the Physical Plant staff decided to use the best of the more heavily resinated fabrics available.

The method used to put up the canopy has changed over the years as well. The first time the old one was used, there wasn't time to install the rigging fixtures on the roofs of the buildings surrounding the court, so side rigging cables to Buildings 3 and 4 went through the windows of offices, much to the annoyance of their occupants. Five rear cables were secured to steel bands placed around the tops of the Building 10 columns. Professor Milgram cemented strips of soft rubber inside the bands to prevent damage to the soft sandstone.

As fate would have it, although the initial reason for the canopy was to create shade, it rained during the first outdoor Commencement exercises. With the canopy's low pitch angle that first year, the rainwater puddled on top, which worried organizers. "I was standing on a ledge outside a third-floor window on Building 4, shaking a rigging cable as vigorously as I could, trying to make the water come off," Professor Milgram recalled.

The old canopy tore once again during installation last year, and workers had to scramble to find a company that could repair it in time. That turned out to be Doyle Sailmakers of Marblehead, MA. "Because they were so good, they got the job of making the new one," he said.

A version of this article appeared in MIT Tech Talk on June 7, 1995.

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