Progress > March 2008
Raising the Roof
March was a big month for Kroon Hall. First, the final big concrete pours for the service node and top floor slab took place. And, once the concrete placements were completed, the roof beams began to rise. In one month the construction site was transformed from a fairly abstract concrete rectangle, to a graceful skeletal form of wood, steel and concrete, reminiscent of the hull of an upturned boat.
If the personality of Kroon Hall is starting to emerge, it is largely due to the glulam roof supports, which are custom-built Douglas-fir beams from Goodfellow Inc. in Québec. Glulam is shorthand for glue-laminated timber, a process by which the one-inch thick Douglas-fir boards were stacked, bent around a template to form the desired arching shape, held in this shape by hydraulic press, and glued while under pressure. After the steel forms were removed, the engineered wood retained its shape and was milled for the specifications of the building.
Each of the glulam arches is composed of two pieces. Once delivered to the construction site, the arch was assembled on the ground (the two pieces are held together by a center pin at the peak of the roof ridge), and lifted as one unit. The combined weight of the arch and rigging equipment is just less than 10,000 lbs. The Kroon Hall roof will be supported by 21 main glulam arches, with two smaller arches cantilevered off at each end.
Once the final arch is swung into place in early April, the construction team will add the roof decking, which Chris Meyer from Turner Construction describes as a really big version of a hardwood floor, with three-inch thick tongue and groove Douglass-fir planks. This roof diaphragm will not only protect building users from the elements, but also brace the structure and distribute the wind load.
The wind speed at roof level has been very apparent due to the rapid flapping of a Yale flag placed at the top of the first roof arch at the east end of Kroon. An American flag will fly on the westernmost arch as a tribute to the “topping out” tradition of ironworkers when constructing skyscrapers and bridges. While completion of the building is still nine months away, this milestone of maximum height is a big one.
Photographs by Peter Otis
Edward P. Bass
Susan & Coleman P. Burke
Michael F. O. Harris Family
Carl W. Knobloch, Jr.
Mary Jane & Richard E. Kroon
Evelyn and Bonnie Lee
Diana Calthorpe & Jonathan F. P. Rose
Joan O. L. Tweedy
William D. Waxter III
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