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Reply #87: "..analysis of sample K-16 yielded no revelations on the collapse.." [View All]

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Make7 Donating Member (1000+ posts) Send PM | Profile | Ignore Wed Aug-23-06 08:39 PM
Response to Reply #81
87. "..analysis of sample K-16 yielded no revelations on the collapse.."
Single Column K-16

The third example of a unique damage feature of a perimeter column was found on sample K-16. (As discussed below, a piece sectioned from this column prior to arrival at NIST was studied and reported on in the Federal Emergency Management Agency [FEMA]/Building Performance Assessment Team [BPAT] [McAllister 2002] report, Appendix C.) This was a single, unidentified column that experienced what appeared to be a large amount of material degradation as a consequence of erosion/corrosion processes, Fig. 620. Of all the recovered steel examined, this was the only case where this type of degradation was observed on a perimeter or core column. The damage consisted of localized thinning in the outer and inner web plates in this area, leading to significant perforations in the outer and inner webs. The stampings at the base of the column on the flange indicated that it was a 50 ksi column with column type 143. The database of all columns showed that columns matching this description were no higher than the 52nd floor level in WTC 1 and the 53rd floor level in WTC 2. Therefore, it was unlikely that this column experienced degradation prior to the collapse of the towers. The attrition appearance of the column, in terms of the two webs experiencing the highest degree of degradation with minimal attack observed on the flange sections, also indicates that the column was in a horizontal position while the attack occurred.

  <- snip ->

The wasting of the web plates most likely resulted from a high temperature, corrosion process that was exacerbated by the presence of sulfur. While not enough evidence was available to indicate whether corrosion occurred through gaseous, liquid, or solid attack (in addition to varied conditions possible in the rubble pile and lack of information associated with the recovery of this column at the WTC site), it was likely that the degradation process was most likely a complex combination of these three. As sulfur was not readily available in large amounts in the steel (0.02 weight percent max.), an external source must have supplied this specie (e.g., plastic, rubber). Viewing the column, this external source was in all probability burning directly on top of the outer web while the column lay in a prone position.

  <- snip ->

While analysis of sample K-16 yielded no revelations on the collapse mechanism for the buildings, the changes in the web material as a result of high temperature corrosion exposure were interesting.

DIAL-UP WARNING: The following file is 40MB.
http://wtc.nist.gov/NISTNCSTAR1-3Cchaps.pdf

Apparently they did not think it was relevant.

- Make7
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