In his letter to the editor, WTC Disagreements, Lawrence Fisher stated that the World Trade Center towers might have been more resilient if they had been configured with a strong and stiff perimeter structure (ENR 11/29/03 p. 5). In fact, they were. The structural system used in the towers was a very strong and stiff perimeter lateral and gravity system with a gravity-only core system. I strongly support the premise of the original article that there was nothing wrong with the design of the World Trade Center towers.
CHARLES J. CARTER Chief Structural Engineer/American Institute of Steel Construction Inc. Chicago