The Pile-Driver Theory
The Tops of the Towers as Giant Sledgehammers
The pile-driver theory takes up where the column failure theory leaves off, explaining how the top each tower crushed the intact portion into oblivion.
The pile-driver theory existed, at least implicitly, since the day of the attack. The paper by Bazant and Zhou contains the essential idea.
|Ronald Hamburger, who co-authored Chapters 1 and 2 of FEMA's Report has given public appearances supporting the official story.|
Structural engineer Ronald Hamburger articulated the pile-driver theory by name, stating to an audience on November 29, 2001:
The pile-driver theory receded with the ascendancy of the truss-failure theory, which abandoned the idea of the entire top sections of the Towers falling as intact blocks. Instead, FEMA told us, the unsupported heights of the freestanding columns, lacking the lateral support of the pancaked floor diaphragms, buckled and collapsed:
Thus, FEMA never invokes the pile-driver theory, preferring to have us believe that the Towers simply fell apart as a consequence of the alleged floor pancaking.
In early 2005, with the release of some of the preliminary reports from NIST's investigation, it became apparent that the pile-driver theory was poised for a come-back. The nearly 300-page Draft of NIST's Final Report on the Twin Towers has only one paragraph describing the start of each Tower's collapse, but the pile-driver theory is unmistakable. The following passage describing the South Tower is almost identical to the one describing the North Tower.
Apparently in response to criticisms that the Draft Report "does not actually include the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable", the Final Report added a new section making the pile-driver theory more explicit. It reads, in part:
The structure below the level of the collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structures below to absorb that through energy of deformation. 3
2. Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Towers, NIST.gov, , page 146
3. Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Towers, NIST.gov, , page 146