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mhgaffney · 07-15-2009, 05:24 PM

Lone Bolt,

It's clear from the above exchange that Mark Roberts did not read the NIST Report.

The information about factor of safety is there in the report -- as I stated. In fact, the NIST scientific team actually guided me to that table. However the data is expressed as demand/capacity ratios instead of factor of safety.

However, the data is the same. It's like the difference between conductance and resistance. Both express the same idea in a different way. Same deal here.

If you simply express the demand capacity ratio in decimal form instead of as a fraction you have factor of safety.

All of this was explained to me by Ron Hamburger, one of the nation's leading structural engineers. I call him up to consult -- and he was most helpful. Hamburger helped author the FEMA study of the WTC collapse.

The core columns had a factor of safety on average of 2.1. Mark Roberts got this totally wrong. His numbers are funny. I have no idea where they came from.

This means that on average any column could support more than twice the anticipated design load (2.1 times to be exact) BEFORE reaching the yield point, where damage and deformation could begin to occur. Notice, this does NOT mean that once the yield point is reached you get a collapse.

No, steel is so resilient that even if the yield point is exceeded it has reserves of strength. You would get a slow gradual deformation. Not a general collapse. Its why structural steel is such a terrific building material.

BTW, the outer perimeter wall had a factor of safety of 5.7. This was a phenomenally strong wall -- On 9/11 -- because there was almost no wind -- the outer wall could support almost 6 times the anticipated design load before damage would begin to occur.

The WTC was incredibly strong -- vastly overbuilt.

07-15-2009, 05:24 PM	#6
mhgaffney Ring of Famer Join Date: Apr 2006 Posts: 9,764	Lone Bolt, It's clear from the above exchange that Mark Roberts did not read the NIST Report. The information about factor of safety is there in the report -- as I stated. In fact, the NIST scientific team actually guided me to that table. However the data is expressed as demand/capacity ratios instead of factor of safety. However, the data is the same. It's like the difference between conductance and resistance. Both express the same idea in a different way. Same deal here. If you simply express the demand capacity ratio in decimal form instead of as a fraction you have factor of safety. All of this was explained to me by Ron Hamburger, one of the nation's leading structural engineers. I call him up to consult -- and he was most helpful. Hamburger helped author the FEMA study of the WTC collapse. The core columns had a factor of safety on average of 2.1. Mark Roberts got this totally wrong. His numbers are funny. I have no idea where they came from. This means that on average any column could support more than twice the anticipated design load (2.1 times to be exact) BEFORE reaching the yield point, where damage and deformation could begin to occur. Notice, this does NOT mean that once the yield point is reached you get a collapse. No, steel is so resilient that even if the yield point is exceeded it has reserves of strength. You would get a slow gradual deformation. Not a general collapse. Its why structural steel is such a terrific building material. BTW, the outer perimeter wall had a factor of safety of 5.7. This was a phenomenally strong wall -- On 9/11 -- because there was almost no wind -- the outer wall could support almost 6 times the anticipated design load before damage would begin to occur. The WTC was incredibly strong -- vastly overbuilt.