Reply #151: Hey einstein [View All]

There were no concrete support columns.

The support columns were steel, not concrete. They only concrete in the WTC was the 4" of topping poured over the steel floor decking. Concrete is very string in compression but has almost zero strength in tension. All of those floors tumbling and being twisted and contorted coming down...it's really quite obvious why the concrete topping was pulverized.

I recommend taking a structural concrete 101 course and you will learn the properties of concrete instead of relying on nutjob conspiracy kooks for your information.

Read this:
http://www.nist.gov/public_affairs/releases/wtc_latest_findings_1004.htm

FACT SHEET

Leading Hypotheses for the Collapses of the World Trade Center Towers

The National Institute of Standards and Technology (NIST) World Trade Center (WTC) investigation team has formulated the chronological sequence of major events leading to the eventual collapses of the WTC 1 and WTC 2 towers as a result of the terrorist attacks of Sept. 11, 2001. The leading collapse hypothesis for each tower is based on evaluations of the building’s innovative structural system; the effects of the aircraft impact and subsequent fire; the post-impact condition of the fireproofing; the quality and properties of the structural steel used in construction; and the relative roles in the collapse scenario played by the perimeter and core columns, and the composite floor system (including connections).

The two collapse hypotheses are consistent with all evidence currently held by NIST, including photographs and videos, eyewitness accounts, and emergency communications records. However, the hypotheses released today still may be revised for the investigation team’s final report, scheduled for release as a draft document for public comment in December 2004 or January 2005.

The leading collapse hypothesis for each tower is as follows:

WTC 1

Aircraft impact damaged the perimeter columns, mainly on the north face, resulting in redistribution of column loads, mostly to the adjacent perimeter columns and to a lesser extent, the core columns.
After breaching the building’s perimeter, the aircraft continued to penetrate into the building, damaging floor framing, core columns and fireproofing. Loads on the damaged columns were redistributed to other intact core and perimeter columns mostly via the floor systems and to a lesser extent, via the hat truss (the steel structure that supported the antenna atop the towers and was connected to the core and perimeter columns).
The subsequent fires, influenced by the impact-damaged condition of the fireproofing:

Softened and buckled the core columns and caused them to shorten, resulting in a downward displacement of the core relative to the perimeter. This led to the floors (1) pulling the perimeter columns inward, and (2) transferring vertical loads to the perimeter columns; and
Softened the perimeter columns on the south face and also caused perimeter column loads to increase significantly due to restrained thermal expansion.

Due to the combined effects of heating on the core and perimeter columns, the south perimeter wall bowed inward and highly stressed sections buckled.
The section of the building above the impact zone began tilting to the south as the bowed south perimeter columns buckled. The instability rapidly progressed horizontally across the entire south face and then across the adjacent east and west faces.
The change in potential energy due to the downward movement of the building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.
WTC 2

Aircraft impact damaged the perimeter columns, mainly on the south face, resulting in redistribution of column loads, mostly to the adjacent perimeter columns and to a lesser extent, the core columns.
After breaching the building’s perimeter, the aircraft continued to penetrate into the building, damaging floor framing, core columns and fireproofing. Loads on the damaged columns were redistributed to other intact core and perimeter columns mostly via the floor systems and to a lesser extent, via the hat truss.
The subsequent fires, influenced by the impact-damaged condition of the fireproofing:

Caused significant sagging of the floors on the east side that induced the floors to pull the perimeter columns inward on the east face;
Softened and buckled the core columns on the east side and caused them to shorten, which transferred significant additional load to the perimeter columns on the east face primarily through the floor system and to a lesser extent, the hat truss; and
Softened some of the perimeter columns that were exposed to high temperatures toward the northern half of the east face.
Due to the additional loads on the perimeter columns on the east face and the inward pulling of those columns, the east perimeter wall bowed inward and highly stressed sections buckled.
The section of the building above the impact zone began tilting to the east and south as both the east perimeter columns and the impact-damaged south perimeter columns buckled. The instability rapidly progressed horizontally across both faces and across the north face.
The change in potential energy due to the downward movement of the building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.