Alumna answers question, "What are you working on?"
Above: 30-foot dragon in Lincoln Center’s plaza for the Game of Thrones season 4 premiere.
By Miriam G. Paschetto (MS 00)
A little over 15 years ago I started work at Geiger Engineers – shortly after getting my master’s degree from University of Illinois at Urbana-Champaign. Geiger Engineers was founded in the late 1980s by David H. Geiger, a pioneer in designing air-supported fabric roofs for sports stadia which proliferated in the 1970s and 80s (the Metrodome and Silverdome are prominent examples). From this specialty, Geiger Engineers has branched out into retractable fabric roofs, tensile membrane structures, arenas, long-span roof systems and entertainment engineering. Being a part of Geiger Engineers gives me the best of all worlds. I get to work on a wide range of projects from arenas to retractable roof components to reviewing outdoor stages for music festivals.
Right now I’m managing several small projects (more about that later) along with working on the construction phase of the new Louis Armstrong stadium at the U.S. Tennis Center in Queens, New York where the U.S. Open is held. The new Armstrong stadium will have a retractable roof and is scheduled to open in 2018. In the meantime, details of the project are under wraps.
However, at the 2016 U.S. Open the new retractable roof built on the existing Arthur Ashe stadium debuted. Geiger’s one Principal who is a mechanical engineer designed the mechanical systems that operate Ashe’s roof. The roof consists of two panels that each nominally cover a 232 foot wide opening. Mounted on the north and south edges of the fixed roof are tracks along which the custom-built wheeled bogies supporting the retractable panels move. The tracks are curved to match the fixed roof’s profile and have a maximum slope of 20 degrees. Operation of the retractable panels is by a pull-cable winch system and four sets of brakes allow the roof panels to be locked at any point in their travel. The maximum cable tension exerted is 140 kips and the maximum vertical load on one bogie is on the order of 500 kips.
My job was to analyze the structure of the wheeled bogies supporting the moving roof panels. To reduce the demand on the trusses making up the roof panels, the bogies were “guided” on one side of each roof panel and released on the other. Taking the axis of the panels’ tracks as x and z as global vertical, the connection of the roof panels to every bogie needed to be free to rotate about the y-axis. This was achieved by an 18” diameter pin through the body of each bogie. Additionally, for the released side bogies the 18” pins were approximately 2.5’ longer than the bogie was wide so that the pins allowed not only rotation about but also translation along the y-axis.
But back to some of my small projects, which can also be very interesting. Geiger’s office is about 30 miles northwest of New York City and this means we also work on a lot of small and sometimes large entertainment and event projects. Things like a 30-foot dragon in Lincoln Center’s plaza for the Game of Thrones season 4 premiere or the reconfigurable temporary truss stage structures for Puebla’s 150th Cinco de Mayo celebration in Mexico or all of the outdoor structures and stages for the Electric Zoo 2016 music festival in New York City. I’ve had projects at Radio City Music Hall, the Reuters building and the Hard Rock Cafe in Times Square, and Broadway theaters. The work is always different and more often than not has a very compressed time-frame. We have to be creative and think on our feet.
At the moment, the absorbing small project I am working on is not entertainment but the retrofit of a ca. 1920s brick building in Manhattan. New York City has a surprisingly large number of very old building stock. For instance, many brownstones date back to the mid- to late-1800s.
In this case, the building owners needed to replace and repair the south parapet of the roof. In the process of removing the existing parapet masonry, the bearing ends of the cinder concrete-encased steel roof beams were exposed. After what must have been decades of water infiltration around the edges of this roof, some of the steel was dangerously corroded. Saying it was barely there is not too strong a description as can be seen in the photograph below. We were left wondering how the roof had remained intact.
It is fascinating to be able to see the “guts” of these old buildings and to try to figure out what the builder was thinking. When we opened up the original drop ceiling (metal mesh that had been directly plastered onto from below – these were typical and are very heavy), we saw that the east and west walls had round bar ties connecting them to the interior roof beams. But for some reason we’ll never know, the ties in the northeast corner were never installed. And indeed, that portion of the wall has visibly pulled away from the roof. Another condition to be addressed in our retrofit design.
The owner is a non-profit so we brainstormed repairs that could be relatively easily done without replacing the entire roof. We are still working out some of the issues but for the roof beam end corrosion, our idea is to chip away the encasing concrete far enough along each beam end to expose a not yet determined length of sound steel. We are not going to disturb the beam bearing plates at the walls but we also do not want to continue depending on them. Small channels will be bolted on both sides of the roof beam webs where the steel is good. These channels will extend to the wall where they will be grouted in place thereby directly transferring the beam end reactions to the masonry wall.
And, as always, I’m looking forward to the next engineering challenge, large or small!
All photos courtesy of Miriam G. Paschetto
Originally published in the Summer 2017 issue of the CEE magazine. If you would like to write about one of your projects for a future issue of the magazine, please contact Celeste Arbogast, firstname.lastname@example.org, for details.