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I thought the history of the World Trade Center Twin Towers layout might be an interesting piece of history. This history was written by my friend, William B.F. Lair, a surveyor of the "first order", written shortly before he died in 1987.
The actual control network was established in 1960. The control network was "tied into" NGS control in both New Jersey and New York, and we quickly realized that the NGS control needed to be "tightened up". The NGS was very cooperative in training and helping us to increase the precision of their control points we were using..this included not only the horizontal but also the vertical control. Once a control network was established into the site, the "Existing Conditions" survey began, and was finally completed shortly after Minoru Yamaski began the design process in late 1962. It is interesting to note that the control, existing condition surveys and plans cost over $5,500,000.00! During the design process, Mr. Yamaski and Mr. Roth's firms required another $250,000.00 worth of surveying to answer questions that were raised.
Once the design was finalized and construction was scheduled was scheduled, Tishman Realty and Construction hired us to provide both vertical and horizontal control onto the site. It was almost instantly realized that because 15 square blocks were to be razed, we needed a dense network of highly precise control outside of that 15 block area from which we could continually extend control onto the site. This control, on its outer perimeter was required to be 1/150,000 horizontally and 1/20000 vertically. As a result, the control had to be placed where heavy traffic, vibrations, extreme temperature changes, etc would not affect the control. In addition, it had to be in positions where we could extend control points directly onto the construction site. For example the depth of the "hole" to the piling covers/column pads was approximately eight stories below ground level; this required having control very close to the actual excavation. In addition, the heavy construction in the area made protecting the control from destruction almost impossible and required us to be ready on almost a moments notice to extend new control back onto the site. It should be noted that all the control was required to be done by Licensed Land Surveyors but all construction layout was done by unlicensed surveyors who were considered to be experts in construction layout. Being sure the control we gave the construction surveyors weighed heavily on us!
We did get involved in the construction survey in the sense that we were required to check both the alignment of the columns and the elevations of the spandrels at every floor, at the eight corners of each floor. The reason we checked only the corners was because the floors were considered a plane and were not parallel to the earth's surface, but the columns were designed to project to the earths center and thus both towers were to be 0.0136 feet wider at the top than at the bottom!
The vertical and horizontal alignment problems were accentuated by the fact that uneven heating of the buildings surfaces and winds (causing sway) made these measurements extremely difficult to make.
In spite of all of these facts, the two towers were finally completed in 1973.
(DCG's added note: Twenty eight years later, the Towers which had taken five years to build came down in a few terribly long minutes!)
David C. Garcelon with credit to my friend Willy Lair.