As Yoders points out in his own rebuttal, the term “top down” has been used since seven U.S. buildings were constructed by IED and TTG (Thornton Termohlen Group) between 1962 and 1974 with the LIFTbuild method. Those projects were built in the San Francisco Bay area, the Port of Los Angeles, Huntington, W.Va. and New York City. McNally erroneously describes the article subject and project as lift-slab construction, which stopped after the 1987 L’Ambiance Plaza apartment building collapse in Bridgeport, Conn. that killed 28 workers.

After my firm, Thornton Tomasetti, delivered its investigation of the Bridgeport accident to the city, lift-slab projects ended. But TGE Top Down has continued, and TGE and its predecessors use a very different system: slip-formed concrete cores that are at 28 days strength before the first floorlifting takes place.

It is outrageous that McNally and others are still spreading rumors about a system that bears no resemblance to the spindly, unstable and unbraced steel columns of the Bridgeport project—a true house-of-cards approach that allowed the building to collapse.

Robert T. Williams is even further from the mark with his allegation—about the Detroit project—that “this system would shake loose like a can of nuts-and-bolts in California or any earthquake.” He goes further astray by writing that these “types of articles are misleading and give little prudence to safety and only highlight production.” How can anyone say that about a building system used on four San Francisco area structures that withstood 1989’s Loma Prieto earthquake with only minor damage?

Jeff Yoders’ rebuttals to McNally and William were excellent, but I thought more was needed. It is amazing how gadflies can make outrageous statements without justifying them.

Charles H. Thornton, Ph.D, P.E. Chairman, TGE TOP DOWN

Easton, Md.