It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Thank you.
Some features of ATS will be disabled while you continue to use an ad-blocker.
Originally posted by wecomeinpeace
I honestly don't see any concrete in any of those photos. Even the last one which is supposed to be "the one surviving piece of concrete core wall", I don't see diddly squat.
Seems to be a red herring, IMO.
The most noticeable change in the modern high-rise construction is a trend to using more steel and shaping lightweight steel into tubes, curves, and angles to increase its load bearing capability. The WTC has tubular steel bearing walls, fluted corrugated steel flooring and bent bar steel truss floor supports. To a modern high rise building designer steel framing is economical and concrete is a costly material. For a high-rise structural frame: columns, girders, floors and walls, steel provides greater strength per pound than concrete. Concrete is heavy. Concrete creates excessive weight in the structure of a building. Architects, designers , and builders all know if you remove concrete from a structure you have a building that weights less. So if you create a lighter building you can use columns, girders and beams of smaller dimensions, or better yet you can use the same size steel framing and build a taller structure. In News York City where space is limited you must build high. The trend over the past half-century is to create lightweight high buildings. To do this you use thin steel bent bar truss construction instead of solid steel beams. To do this you use hollow tube steel bearing walls, and curved sheet steel (corrugated) under floors. To do this you eliminate as much concrete from the structure as you can and replace it with steel. Lightweight construction means economy. It means building more with less. If you reduce the structure’s mass you can build cheaper and builder higher. Unfortunately unprotected steel warps, melts, sags and collapses when heated to normal fire temperatures about 1100 to 1200 degrees F.
The fire service believes there is a direct relation of fire resistance to mass of structure. The more mass the more fire resistance. The best fire resistive building in America is a concrete structure. The structures that limit and confine fires best, and suffer fewer collapses are reinforced concrete pre WWII buildings such as housing projects and older high rise buildings like the empire state building, The more concrete, the more fire resistance; and the more concrete the less probability of total collapse. The evolution of high- rise construction can be seen, by comparing the empire state building to the WTC. My estimate is the ratio of concrete to steel in the empire state building is 60/40. The ratio of concrete to steel in the WTC is 40/60. The tallest building in the world, the Petronas Towers, in Kula Lumpur, Malaysia, is more like the concrete to steel ratio of the empire state building than concrete to steel ratio of the WTC. Donald Trump in New York City has constructed the tallest reinforced concrete high-rise residence building.
Originally posted by Zaphod58
From one page that I read, the WTC was 60/40 concrete to steel ratio, but with the WTC it was estimated to be 40/60 concrete to steel. So from what they're saying there WAS concrete, but it was MUCH less than in previous and most high rise buildings.
The most noticeable change in the modern high-rise construction is a trend to using more steel and shaping lightweight steel into tubes, curves, and angles to increase its load bearing capability. The WTC has tubular steel bearing walls, fluted corrugated steel flooring and bent bar steel truss floor supports. To a modern high rise building designer steel framing is economical and concrete is a costly material. For a high-rise structural frame: columns, girders, floors and walls, steel provides greater strength per pound than concrete. Concrete is heavy. Concrete creates excessive weight in the structure of a building. Architects, designers , and builders all know if you remove concrete from a structure you have a building that weights less. So if you create a lighter building you can use columns, girders and beams of smaller dimensions, or better yet you can use the same size steel framing and build a taller structure. In News York City where space is limited you must build high. The trend over the past half-century is to create lightweight high buildings. To do this you use thin steel bent bar truss construction instead of solid steel beams. To do this you use hollow tube steel bearing walls, and curved sheet steel (corrugated) under floors. To do this you eliminate as much concrete from the structure as you can and replace it with steel. Lightweight construction means economy. It means building more with less. If you reduce the structure’s mass you can build cheaper and builder higher. Unfortunately unprotected steel warps, melts, sags and collapses when heated to normal fire temperatures about 1100 to 1200 degrees F.
The fire service believes there is a direct relation of fire resistance to mass of structure. The more mass the more fire resistance. The best fire resistive building in America is a concrete structure. The structures that limit and confine fires best, and suffer fewer collapses are reinforced concrete pre WWII buildings such as housing projects and older high rise buildings like the empire state building, The more concrete, the more fire resistance; and the more concrete the less probability of total collapse. The evolution of high- rise construction can be seen, by comparing the empire state building to the WTC. My estimate is the ratio of concrete to steel in the empire state building is 60/40. The ratio of concrete to steel in the WTC is 40/60. The tallest building in the world, the Petronas Towers, in Kula Lumpur, Malaysia, is more like the concrete to steel ratio of the empire state building than concrete to steel ratio of the WTC. Donald Trump in New York City has constructed the tallest reinforced concrete high-rise residence building.
Originally posted by AgentSmith
I love these images:
The Concrete Core And Its Hallways
Below on the left is WTC 1 at sunrise. The view is not looking down the hallways, we look nearly along the long axis of the towers core. The vertical line of light in the lower segment is created by sunlight reflecting off the inner core walls then shining out the core hallway.
The North Tower had a core oriented east and west. The camera perspective is not aligned with the hallway as can be seen by the orientation of the south towers roof indicating an oblique view. The light is reflected off the inner south shear wall at a hallway level where there is no doorway interrupting. Notice the very slight interruptions, dark streaks, whole dark floors. The nature of light under these conditions is to blend, blur and obscure solid areas between the light.
We see no light on the left side because the doorways on the north face do not align with the doors on the east. Above that, or the top sky lobby floor, the top floors had a different scheme with some halls on one floor crossing both directions.
The core of the south tower above is oriented north south with its long axis and had 2 halls crossing the short axis. We see no light through it because the doors on our face only reveal a shadowed inner concrete wall corner. See the 2 vertical, central lines in the image below.
Below: Tower on right, the north tower. The interior box columns followed the slight taper of the concrete core to a point then had to continue vertically plumb to the roof as the interior wall of the outside tube of the steel framework. The purpose of this section and photo is to show the space between the interior box columns and the tapering core face at the upper floors. The north tower had hallways crossing perpendicularly every other floor (diagram below). This picture of the towers is looking due south through the towers.
Above: The north tower core was oriented east west, so we are looking at the wide side. On the right tower fr then project that dddistance down to a cross section. We see, from right to left; a light space from the out side to a dark column which represents the floor space to the interior box column, then there is another narrow light space left of that. That is the space between the interior box column and the concrete core face. Going leftward we see the facing concrete shear wall, then the hallway crossing the narrow axis, then the core face again, then the space between the east core face, then interior box column, then floor space to the east side of the building.
Originally posted by Zaphod58
From one page that I read, the WTC was 60/40 concrete to steel ratio, but with the WTC it was estimated to be 40/60 concrete to steel. So from what they're saying there WAS concrete, but it was MUCH less than in previous and most high rise buildings.
“Beyond the reaction that any citizen has—the sadness that we all feel—you have to understand, I worked long hours, seven days a week on this project back when I was young and energetic,” [...]
Still, Robertson, whose firm is responsible for three of the six tallest buildings in the world, feels a sense of pride that the massive towers, supported by a steel-tube exoskeleton and a reinforced concrete core, held up as well as they did—managing to stand for over an hour despite direct hits from two massive commercial jetliners.
Each tube contained a concrete core, which supported only the load of the central bank of elevators and stairwells (Snoonian and Czarnecki 23).
At the heart of the structure was a vertical steel and concrete core, housing lift shafts and stairwells. Steel beams radiate outwards and connect with steel
uprights, forming the building's outer wall.
The structural design for the World Trade Center Towers was done by Skilling, Helle, Christiansen and Robertson. It was designed as a tube building that included a perimeter moment-resisting frame consisting of steel columns spaced on 39-inch centers. The load carrying system was designed so that the steel facade would resist lateral and gravity forces and the interior concrete core would carry only gravity loads.
Dr. Domel received a Ph.D. from the University of Illinois at Chicago in 1988 and a Law Degree from Loyola University in 1992. He is a licensed Structural Engineer and Attorney at Law in the .State of Illinois and a Professional Engineer in twelve states, including the State of New York. Dr. Domel is authorized by the Department of Labor (OSHA) as a 10 and 30 hour construction safety trainer.
Originally posted by wecomeinpeace
Concerning the pictures of what may be rebar at ground zero, the bars seem to be a little too thick. All the steel rebar I've seen has been at most an inch in diameter. This needs to be explored in more depth.
Could it be that the basements and floors 1-7 were concrete reinforced and the structure above wasn't?
The documentary focused on the concrete core because the construction of the core was a big slowdown factor. The steel contractors, mostly the indigenous tribes of the area, Onandaga, Iroquois, Mohawk, the best high steel erectors in the world, experiences slowdowns in the perimeter and interior column’s construction, not a part of their bids. They had to lay off crew while the concrete limited to 40 feet vert per pour was completed. Later, after complaints the engineers calculated that 7 floors of steel could be built, instead of just 4, while the concrete caught up. Unfortunately the aerial photos cannot see the steel after maybe the 14 floor or so. What you see in the photos are various cranes and equipment used to move material and support the rebar hanging into the concrete pour.
The actual slowdown was when it was revealed by the government agency constructing, that there was a special anti corrosion, anti vibration resistant coating on the rebar of the concrete core structure. The coating was flammable and special precautions were to be taken, meaning the government would handle the butt welding of the 3 inch vertical bar prior to regular crews running the horizontal minor steel.
entire blog here
I remember watching the video of the construction of the towers and there was mention of concrete in the basement. The four-level parking facilities in the basement would also be made from much thicker concrete (and necessarily steel-reinforced) than the floor pans in the office levels.
The fire eventually finished 26 hours later, leaving a complete burn-out above the fifth floor. The steel-glass façade was completely destroyed, exposing the concrete perimeter columns. The steel columns above the 17th floor suffered complete collapse, partially coming to rest on the upper technical floor.