This next paper appeared in the journal JOM, issue 53, December 2001, pp. 8-11. You may read the article here.

The paper was written by Thomas W. Eagar, the Thomas Lord Professor of Materials Engineering and Engineering Systems, and Christopher Musso, a graduate research student. Both are from the Massachusetts Institute of Technology (MIT).

For the most part the paper is very good, however, the speculative aspects are used by some as evidence that the fire-induced collapse scenario is authorative. As before my comments will appear in black and the author's material will appear in blue italics.

Let's begin...

In order to separate the fact from the fiction, we have attempted to quantify various details of the collapse.

The major events include the following:

The airplane impact with damage to the columns.
The ensuing fire with loss of steel strength and distortion (Figure 1).
The collapse, which generally occurred inward without significant tipping (Figure 2).

In order to separate the fact from the fiction, it is important to note that the degree of strength loss and distortion is unknown and never will be known. We do not know if this played a factor in the collapse at all.

The authors then refer to the visual nature of the collapse as being "generally...inward without significant tipping". That's a politically correct term for describing an implosion.

Let's continue...

Of equal or even greater significance during this initial impact was the explosion when 90,000 L gallons of jet fuel, comprising nearly 1/3 of the aircraft’s weight, ignited. The ensuing fire was clearly the principal cause of the collapse

According to Boeing, a 767 carries 23,980 U.S. gal (90,770 l). The authors are assuming that the planes had full fuel loads. According to FEMA's assessment, each aircraft was carrying around 10,000 gallons (37,854 l).

We are then told that "fire was clearly the principle cause of the collapse" without any corroborating physical evidence. Not to mention the fact that no skyscraper, in the history of the US, before or since, has ever collapsed from fire.

This statement is really a shot in the dark and complete speculation.

It is known that the WTC fire was a fuel-rich, diffuse flame as evidenced by the copious black smoke. Soot is generated by incompletely burned fuel; hence, the WTC fire was fuel rich—hardly surprising with 90,000 L of jet fuel available.

Firstly, this black smoke was observed for over an hour, which according to NIST's report, would indicate that it was not due to jet fuel, but rather, burning office contents:

"The jet fuel, which ignited the fires, was mostly consumed within the first few minutes after impact. The fires that burned for almost the entire time that the buildings remained standing were due mainly to burning building contents and, to a lesser extent, aircraft contents, not jet fuel."
Key Findings of NIST’s June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster

Secondly, as we noted earlier, the amount of jet fuel was over-estimated by at 50,000L. Thus, reducing burning time of the fuel and the maximum coverage by 5/9ths the origonal estimate. It would not, however, impact the burning temperature as noted by the authors. It simply reduced the initial scale and slow the long term progression of the subsequent fire.

Let's continue...

It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.

So, it is noted that structural integrity was not compromised by the impacts and that even a 50% loss of strength would not have induced the collapse.

The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.

This notion has since been demonstrated to be false. In tests conducted by NIST the trusses did not fail, even though they were tested to their maximum design load, which is some 1,300 tons greater than the weight of the floor itself and nowhere near the loads that were on the floors at the time of the collapse.

"Tests were conducted in both the restrained and unrestrained condition to provide bounds on the expected performance of the floor system under the standard fire exposure. The restrained full-scale WTC floor system obtained a fire resistance rating of 1½ h while the unrestrained floor system achieved a 2 h rating. For the unrestrained test condition, specimens protected with ¾ in. thick sprayed fire resistive material were able to sustain the maximum design load for approximately 2 h without collapsing; in the unrestrained test, the load was maintained without collapsing for 3½ h."
Fire Resistance Tests of Floor Truss Systems (Draft)

So, once again, we have another paper that is irrelevent to any factual discussion on the collapse of the WTC.