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Hardfire: Szamboti / Chandler / Mackey

Newtons Bit said:
I think, in general, concrete buildings are still more susceptible to progressive collapse than steel structures. There's a number of reasons for this, but the simplest explanation is that concrete requires rebar to resist tension forces. If that rebar isn't in the right location and detailed correctly an entire concrete section could fail from load redistribution, the capacity of the original section before the collapse is irrelevant. With steel, the entire structure is capable of resisting both compression and tension. It's quite common for a steel structure to have good resistance towards single column failures. Concrete structures, on the other hand, have to be specifically designed for that load redistribution (and it's not required by code for most buildings).
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Excellent comments.
 
Tony,

Do you have any physical evidence to show everyone here that thermite or explosives were used on 9/11?

Can you account for the primacords, the shaped charges & 1,000's of pounds of thermite?
 
jaydeehess said:
In addition, concrete must be allowed proper time to cure before load is applied and if the construction pace pushes this time is combined with adverse temperature and humidity conditions that slow the curing disaster can occur.

With steel, it goes up, gets attached and is ready.
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I believe most of the concrete structure progressive collapses that have ever occurred were for the reason you cite.
 
Originally Posted by Newtons Bit
I think, in general, concrete buildings are still more susceptible to progressive collapse than steel structures. There's a number of reasons for this, but the simplest explanation is that concrete requires rebar to resist tension forces. If that rebar isn't in the right location and detailed correctly an entire concrete section could fail from load redistribution, the capacity of the original section before the collapse is irrelevant. With steel, the entire structure is capable of resisting both compression and tension. It's quite common for a steel structure to have good resistance towards single column failures. Concrete structures, on the other hand, have to be specifically designed for that load redistribution (and it's not required by code for most buildings).
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Tony Szamboti said:
Excellent comments.
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Portland Cement Association has a different opinion:


“A major advantage of concrete construction for high-rise buildings is the material's inherent properties of heaviness and mass, which create lateral stiffness, or resistance to horizontal movement. Occupants of concrete towers are less able to perceive building motion than occupants of comparable tall buildings with non-concrete structural systems. As a result, concrete has become the material of choice for many tall, slim towers, including many squeezed into narrow building lots in New York City in recent years. Engineers deemed concrete to be the only viable structural option for the structures—including City Spire on West 56th Street, with its slenderness ratio of 10 to 1—to withstand anticipated wind loading. …”

When subjected to abnormal loads how do concrete and steel buildings perform:

“Contrary to popular belief, a structure's likelihood of surviving an earthquake depends more on how well the structure is engineered than on what type of material is used to build it. During a severe earthquake that struck Kobe, Japan, on January 17, 1995, concrete buildings and steel buildings in the downtown area of the city shared comparable fates: just 4.9 % of concrete buildings and 5.3 % of steel buildings collapsed.”

http://www.cement.org/buildings/overview.asp

Whereas most steel high rise office buildings have a column and beams grid floor systems (as in the Towers core area) every 900 square feet or so that can compartmentalize and aid in arresting progressive collapse , the almost structurally unique Towers had 31,000 square feet of interior floors unsupported by any interior columns or beams. This design combined with light, fire unprotected, high-perimeter steel area to mass ratio fire exposure of the web joists contributed to the building’s progressive collapse.
 
This is far off-topic, BasqueArch, but what exactly is the different opinion? They mentioned detailing for seismic resistance. This is not quite the same as detailing for progressive collapse resistance, though frequently seismic details provides strength against progressive collapse.

Concrete buildings in non-seismic regions do not have the ability to withstand column failures. They're just not detailed for it. The Murrah building is a good example of this. Steel structures, such as those at the WTC, have an inherent ability to resist greater or lesser amounts of column failure.
 
Brittle behavior in concrete can be a benefit in a progressive collapse.

A portion of the Murrah building survived because the collapsing portions broke of, and could not transfer any more of the energy from their collapse into the surviving structure.

Steel structures might exhibit great redundancy and ductility, but this is not a benefit unless you have determined the structure will be stable after new load paths have been found. This is tricky because the post damage configuration might lead to large forces that were not ever accounted for in design.

For example, flooring systems display remarkable damage tolerance due to catenary action, but the resulting anchorage forces can be extremely problematic (sounds familiar....)
 
cmcaulif said:
Brittle behavior in concrete can be a benefit in a progressive collapse.

A portion of the Murrah building survived because the collapsing portions broke of, and could not transfer any more of the energy from their collapse into the surviving structure.

Steel structures might exhibit great redundancy and ductility, but this is not a benefit unless you have determined the structure will be stable after new load paths have been found. This is tricky because the post damage configuration might lead to large forces that were not ever accounted for in design.

For example, flooring systems display remarkable damage tolerance due to catenary action, but the resulting anchorage forces can be extremely problematic (sounds familiar....)
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That's a bug, not a feature. Your argument is akin to saying windows has an added safety feature against hackers because it crashes so frequently and isn't connected to the internet while it reboots.
 
I'm not sure if this is true to the Murah building. The blast accelerated debris, then left an alternate path for the debris to collapse onto (compared to the towrers). In terms of Tony's favourite mass participation, the Murrah had very little. There is a distinct pattern in the building remains that suggests the blast caused the observed collapsed areas, and not falling debris. I think there are different mechanisms at work in the Murrah bulding.
 
alienentity said:
Tony, what caused WTC2 to tilt more than WTC1?
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I noticed that you didn't mention that the two blocks were of different dimensions and sizes. I would have thought that would have been a significant factor, as the upper block of WTC1 was much shorter than the other one. Am I on the right track?
 
Newtons Bit said:
This is far off-topic, BasqueArch, but what exactly is the different opinion? They mentioned detailing for seismic resistance. This is not quite the same as detailing for progressive collapse resistance, though frequently seismic details provides strength against progressive collapse.

Concrete buildings in non-seismic regions do not have the ability to withstand column failures. They're just not detailed for it. The Murrah building is a good example of this. Steel structures, such as those at the WTC, have an inherent ability to resist greater or lesser amounts of column failure.
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NB, as shown by the Kobe ,Japan earthquake both concrete and steel buildings had the same failure rate, so one material was no more inherently weak, when both materials design account for the same forces. Detailed right, both materials can compensate for lost columns.

As I understand it both the concrete Murrah building and the steel WTC7 suffered an initial column failure (one by explosion, one by heat) under transfer beams/girders . So the WTC7 loss of one steel column did not prevent global collapse. Perhaps the lesson here is that transfer beams should not be used in buildings subject to potentially abnormal loads, not what material to use. Embassies choose poured-in-place concrete for blast resistance and thereby survival from collapse.

The main point I want to make is that the steel Towers were not of typical design and were weak to fire and non-redundant in its vulnerable long span non-columned lightweight floor truss design.
(Not that I would have done anything differently.)

For steel buildings either the fire goes out before the building collapses or the building collapses before the fire goes out.
The plane damage and the fires fully explain the gravity-only collapse of the Towers.
 
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I've got a request from you guys. Can those of you who have college/university training in physics and/or engineering please give a brief account of it?

I would like to pass such info onto a group of anti-JREF truthers who seem convinced that nobody on the JREF conspiracy forums has expertise in physics.

Thanks in advance.
 
alienentity said:
I've got a request from you guys. Can those of you who have college/university training in physics and/or engineering please give a brief account of it?

I would like to pass such info onto a group of anti-JREF truthers who seem convinced that nobody on the JREF conspiracy forums has expertise in physics.

Thanks in advance.
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Physics and math (degreed) at the University level, and currently Power Engineering at the college.

A physics expert isn't really that well versed in material science and engineering. We're talking applied science and theoretical. There's a grey area, but I know PhD physics grads that can't change a tire.

What physics does is give you a great base for applying science to things. Ryan is a great example of this. He's probably spent more time on this 9/11 crap than he did on his undergrad. If not more, then he's certainly approaching that point.

It isn't about degrees, it's about understanding. Period. All a degree does is give you a piece of paper that says "This guy gets it".

My degree says "He kinda gets it, but just barely" :)
 
alienentity said:
I've got a request from you guys. Can those of you who have college/university training in physics and/or engineering please give a brief account of it?

I would like to pass such info onto a group of anti-JREF truthers who seem convinced that nobody on the JREF conspiracy forums has expertise in physics.

Thanks in advance.
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Here is mine...although none of it related to 9/11 issues....

Military:
8 years in the Army Reserves specializing in Communications....deployed from 2004-2005 during OIF2. Left the service in 2006.

Civilian:
Bachelors of Science in Electrical Engineering.
Almost 7 years of experience.

Areas of focus:Electronic Warfare (EW) and Intelligence Surveillance and Reconnaissance (ISR) systems and sensors.

Role: Testing and Evaluation during field and lab testing.

Other areas: Directed energy weapons (DEW).

Thats the shortest and most general description I can give ya...

***Edited to add: Nevermind...it looks like you already got what you needed....***
 
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