<-- Photo is from page 238 of Joel Meyerowitz'
AFTERMATH
The non-diagonally gusseted (orthogonal) columns supporting the core of the Twin Towers were joined end-to-end by a deep weldment running along their longest ajoining faces. In the event this type of joint need be broken in a controlled demolition, a charge is placed on this joint, the explosive force of which severs the joint. In doing so, the force of the blast also bends the surface of the column inward, resulting in a concave deformation of the end of the beam.
Examples of column segments with characteristically deformed ends are shown here. It is relatively easy on close inspection to determine if a deformation was formed from a detonation or by impaction as in being struck by other extremely heavy debris falling from great heights or horizontally by a transport vehicle travelling at speed. Since the force from an explosion is applied by rapidly expanding gas more or less uniformly over the affected area, originating from a single point at the locus of the explosive device, the deformation is that of a gentle curvature, free of impact marks made by being struck by another hard object, and with the center of the arc thus formed in the general area of the demolition charge. One formed by striking from another structural member is characterized by sharper deformation angles and gouges or scrapes where the two pieces collide. Also, because the force of a detonation is applied by gas uniformly over an area, curvatures in the rubble can be free of the local stress failures characteristic of being mechanically cold-forged.
Note also that due to the high percentage of oxidizers present in explosives, steel will show a
characteristic oxidation if an explosive is detonated in close proximity. Quite a number of photos
from The Pile show this light red oxidation on the beam ends.
A perusal of the hundreds of photos of The Pile that have managed to make it into the public domain indicates that the observable deformation of steel beams due to impact after falling from a great height is substantially less than the concavities shown here.
One can only conjecture how many beams presented with these concavities, and whether these were formed detonatively or from impact, since the evidence, contrary to US statutes pertaining to crime scene evidence, was rapidly shipped overseas as scrap to be melted down. One can find numerous examples of beams with ends distorted smoothly inwardly in the FEMA 9/11 Photo Archive.
Select "Open this Image" of FEMA Photos 4166, 4204, 4154, 5432,5381 to view in higher detail
In light of this, one can only guess, also, the motives of certain New York authorities who placed a very strict ban that prevented tourists and other laypersons from photographing the World Trade Center's remains.
What is certain is that no-one has yet been held accountable for this destruction of evidence by any agency vested with that authority by the US Government.
Now let's use that same forensic analysis to shed a little light on what hit the Pentagon. Since some of the pillars damaged in the Pentagon were concrete reinforced with steel rods, we need to enlarge on our understanding that structural members subject to an explosive blast 1) curve into arcs with a center toward the detonative device, 2) are characterized by an absence of impact scarring, and 3) show an oxidized surface.
Concrete, being rigid, responds to modern detonators by shattering into dust. The large pyroclastic clouds seen at the World Trade Center were composed largely of that dust. If a reinforced concrete pillar were subject to a collision with a rapidly moving hard object, one would expect to see localized deformation where it had been hit, with major cracking extending into the more intact area. The concrete would be broken into relatively large blocks, as we see in concrete buildings that succumb to earthquakes.
On the other hand, we would expect to see reinforced pillars exposed to a detonation having their concrete shattered out of them, and the remaining structure, if standing at all, would take on the characteristic arc, with a center pointing toward the source of the detonation.
Most of FEMA's photos are of people standing around congratulating each other for acts of heroism, admiring their dogs or helping themselves to catered lunches at the disaster site. Occasionally, however, the astute observer can find a forensically interesting shot.
FEMA Photo 4436
Note, that in this picture of the Pentagon's interior, the electical conduit on the pillar near the center does not appear to have been hit by anything solid, yet the pillar to which it was attached has lost its structural integrity. The concrete has been totally blasted out of the pillar on the extreme right. Note also the center of the blast appears to have been outside the exterior wall of the building.