Working with the team designing the World Trade Center Tower 1 from 15 May 2003 until 15 December 2003, Guy Nordenson and Associates developed the design and structure that has served as the design basis for the World Trade Center Freedom Tower. The original WTC T1 design is a torqued and tapered volume beginning as a parallelogram 200ft by 260ft at street level and transforming to 200ft by 60ft at 2000ft elevation. The Northeast and Southwest corners slope upward at a 1:10 vertical incline while the Southeast and Northwest corners remain vertical "held" corners.
The WTC T1 consists of a 1000ft building, a 700ft cable-stayed double mast structure and a 300ft antenna field and carbon composite tensegrity structure. The building structure uses a steel diagrid exterior frame, a composite steel floor structure and a 110ft by 65ft continuous concrete core. Floor to floor height is 13ft 4in or 15 floors per 200ft module and is optimized for both ceiling and floor supplied ventilation. The diagrid structure facilitates the economical transfer of selected columns over the PATH tracks under the building. Detailed analyses and design studies, including wind tunnel tests, were carried out. Structural steel weights for the building portion are on the order of 19lbs/sf with the all concrete core. The maximum (controlling) torsional acceleration is 27milli-g's for a 10 year return period wind regime. The cable system contributes both stiffness and transparency and provides for a safe means of construction - allowing both slipped-formed cores and a strand jacked tensegrity/antennae platform - and enhanced safety in use. The open cable structure would permit the operation of wind turbines and tests were conducted to evaluate wind turbulence and drag effects on the turbines and cost impacts to the building structure.
photograph by Jock Pottle model by Studio Associates of New York