The Core Structure Of The World Trade Center Towers Was A Steel Reinforced, Cast Concrete, Tubular Core.
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Some in the UK still think the WTC tower core was built as shown below. It was not. The diagram shows what is basically a post-stressed concrete design. Yamasaki had reviewed the design, and found no contractor that could build a 1,300 foot column of that design. We all know the towers had their stairwells and elevators inside the core. There is no room for that in the core below.
The design was a "tube in a tube" construction where the steel reinforced, cast concrete interior tube, was surrounded with a structural steel framework configured as another tube with the load bearing capacity bias towards the perimeter wall with the core acting to reduce deformation of the steel structure maximizing its load bearing capacity. All steel structures with the proportions of the WTC towers have inherent problems with flex and torsion. Distribution of gravity loads was; perimeter walls 50%, interior core columns (interior wall of the outer tube of the tube in a tube construction) 30%, concrete core 20%.
Steel, no matter what temper, no matter what bracing is used, ends up with an overall flex that exceeds design parameters for defining when deformations and failures occur. These were facts I learned from a documentary in 1990 called "The Engineering and Construction of the Twin towers. Yamsaki's decision making process was outlined and rejected core designs identified. Including the plans which have been "leaked". Those plans are altered, faked to appear as plans having revisions and later dates.
Both the WTC 1 & WTC 2 towers had a rectangular cast concrete core structures. WTC 1 was a strict shear wall design having poor access across the core to preserve shear wall strength. WTC 2 had the concrete core formed into rectangular shear wall cells that had more hall floors, elevators and stairways in them.
I've met numerous people that remember the early and very technical 2 hour show. One was a civil engineer who remembers the documentary aired on another cable educational channel in 1995 and remembers the concrete core as they are shown below and labeled "ACTUAL CORE OF WTC TOWERS", but as yet, is not willing to provide a declaration certifying such. The documentary showed us the true concrete core structure of the trade center towers. It aired in 2 segments on consecutive nights. I missed the first 20 minutes of the second one, otherwise I watched it all. Yamasaki's design for a torsion resistant core structure made from non flexible material, steel reinforced cast concrete, won a competition in strength with several others. All steel towers failed high winds because the steel perimeter columns could take the weight but were prone to flexing and the twisting.
The documentary focused on the concrete core because the construction of the core was a big slowdown and substantial challenge.
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 steel breakdown inner forms for the concrete left a very smooth and shiny surface on the concrete. The following link has a more in depth analysis of the towers silhouettes.
Understanding The Silhouetted Images Of The Twin Towers.
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Below I've crudely altered an earlier FEMA core diagram to show how the concrete core of WTC 1, interior walls and hallways were configured through the APROX. bottom 1/2 of north towers "tube in a tube" construction. The hallway scheme went up to the 43rd floor.
Interior walls of the core were not continuos vertically, they were interrupted by hallways perpendicularly opposed with each floor. Doorways appeared on each floor on every face every other floor. The tops of the interior walls of the concrete core served as the support for the steel interior concrete forms that had to be disassembled and lifted 40 feet to be set for the next pour. Exterior forms were plywood.
The hallway/door scheme was changed higher up. Also, the south tower was different, 2 hallways crossed the short axis of the core, perhaps with one perpendicular. See the page Understanding The Silhouetted Images Of The Twin Towers for more detail.
NOTE: WTC 2 was radically different employing a cell/shearwall design that allowed 2 hallways in each direction.
North Tower Core
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What is often referred to as the "cores" in raw photo evidence, and what the photos really show.
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Regarding helicopter photos referred to as pictures of core columns at upper phases:
What you see in the photos of tower construction within the official story are the kangaroo cranes used to move material, the interior forms, and elevator guide rails, or to position the rebar hanging into the concrete pour. The steel framework was built up to 7 floors over the top of the concrete core being constructed inside of the steel frame obscuring the core construction from view. Other photos when the construction is lower show elevator guide rails. These are being miss identified as "core columns" on some web sites.
Photos and the tower construction.
Before another core tier could be formed, the elevator guide rails had to be lowered and set in place to a level 2 floors lower than the top of the present concrete pour. They are what is shown in the diagram at the top of this page, the FEMA core. The guide rails are presented as multiple, narrow rectangular tubes that supposedly ran full length for the tower.
Photos at ground zero.
There is a photo showing the bottom basement foundation level where various columns, cut off, protrude from the concrete bottom. There is a workman near center in the photo wearing brown coveralls, firefighters are in the foreground. These columns are often referred to as "core columns". The columns that rise up from inside the concrete channels forming the interior base of the concrete core are mostly elevator guide rails. To the right of the workman in the background is an interior box column that has a fresh torch cut, at an angle, with slag hanging from the cut. Its dimensions, proportions and thickness are different. The photo is looking across the tower core footprint.
Below is another photo with greater zoom, annotated by someone else for a site that did not know of the concrete core. However, they were informed enough to not try and label the vertical steel inside the core as "MASSIVE BOX COLUMNS" as are the interior box columns ringing the core. Smaller elevator guide rail support steel are seen inside the core area.
Construction photos are being used to misrepresent elevator guide support steel.
Below is an image from the street where butt plats are seen that join the ends of the elevator guide rail support steel. Such joints are not strong enough for "core columns". Core columns must be butt welded with 100% welds as are the interior box columns which surround the core. If these were core columns, they would be seen standing in 9-11 images, they are not.
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If there were the full length steel core columns as shown in the FEMA diagram, where are they in the images below that show the concrete tubular core of WTC 2 standing momentarily, half fallen, without the outer steel framework? Where are the steel core columns in the photos following that?
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WTC 2 CONCRETE CORE STANDING
The core shown on the FEMA site will not leave a spire standing like we see below and no visible multiple, heavy steel core columns are seen in photos. No part of those cores could have this appearance as it is halfway to the ground Above.
I've annotated available images to show what the core I saw being built in the documentary was.
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THE WTC 2 CORE FALLING
Below is an image of the top portion of WTC 2 as it falls and is about to hit WTC 3. I would expect to see doorways, but do not, and assume that the top 2 floors of the concrete core were different structurally than those below where a number of floors had hallways crossing in both directions.
The pink arrow below points to the core. The brownish gray well lit roof and above wall face left are the core. A basic cube shape inside the perimeter walls descending with it.
Below I'll attempt to explain and identify the building elements as they are partially seen inverted and being ripped apart by the free fall descent of a portion of the steel reinforced tubular cast concrete core.
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The upper point of fine red line approximates the location of the top edge of the tower faces at the roof and what was the horizontal plane of the top of the tower.
The fine circular blue line shows the counter clockwise rotation of a group of panels of perimeter box columns that are fastened by floor beams near the top of the tower corner/panel edge, seen left of the green line.
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The fine green line shows the approximate exterior face corner of the building as it falls and the heavy green arrow points to the edge of the perimeter box column panel that was aligned with the fine green line.
The purple arrow has been determined by a photo to be a piece of an adjacent perimeter wall stuck to the falling corner of a north west corner portion of the concrete core.
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THE SPIRE
Below is image of a spire that stood for 14 seconds comprised of one corner of the interior box columns that were fastened to the outside of the concrete core. This connection between interior columns and the concrete made the core a load bearing and anti torsion element for the steel framework configured as a tube around the concrete tube comprised of four smaller vertically interrupted tubular elements formed by the interior core walls.
Below is a photo of the spire from the opposite side. The concrete shear wall of the core and interior walls interrupted by hallways can just be seen.
Below is a zoomed image of the spire with arrows indicating the structural elements.
Following is a photo that shows the face of the concrete shear wall behind interior box columns.
The spire, a composite of an interior box column and a sliver of intact steel reinforced concrete shear wall of the core, fell all at once.
And left the rebar of the core, delaminated from the concrete, standing for a few short seconds as seen below.
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THE REBAR
See the "SPIRE SEQUENCE" page for more detail.
The below photo has a comb like shape of the remnant of the reinforcing bars of the core, briefly standing. The FEMA core cannot leave this shape. There are too many elements and they are too small. The box columns in the spire image above are about the same size as the steel columns the core was supposedly made from. FEMA's information is that there were 47 core columns and they were hand fabricated in 40 foot sections then 100% welded in place. The below photo was taken at approximately the same distance.
Below are a long row of 3" rebar on 4 foot centers seen at approximately 6400 feet.
The slope to the top of the rebar was mentioned in the documentary. Engineers specified that the concrete pours not terminate with level opposing joints across the tower to maximize the strength of the tubular concrete tower core as an anti torsion element. Also the rebar was to be welded in series of butt joints in a slope matching the top of the concrete maximizing torsion resistance of the tube. The slope of the tops of the rebar in the photo below show this.
The above are the tops of 3" rebar, special high tensile steel, that has broken at a series of welds. Again, the slope of the tops of the steel bars is created because engineers did not want a series of weld joints on the vertical bars horizontally creating a possible line of fracture across the building.
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THE BASE OF THE CONCRETE CORE:
The below image shows the interior box columns and a stair well sandwiching the thick base of the core. High tensile steel rebar protrudes from the top of the cast concrete. Considerable recall arrives the memory that 6 inch high tensile rebar was used throughout the foundation and it extended up through the core wall base for a few floors into the tapering concrete core wall.
Annotation shows the location of a APROX. 3'x7' hallway that ran the length of the long axis walls of WTC 1. The silverstein plans, preliminary plans made obsolete by Yamasakis concrete core design, the only design he would certify as safe, show an elevator in that location. This single image proves the concrete core and shows that the plans from silverstein have been faked with the addition of revision tables.
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This is a link to a very large image, same as below, where huge quantities of sand and gravel which all has the color of cement is seen. The official tower core design would produce HALF this much sand with NO gravel at all.
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Below a large triangular piece of the WTC 1 concrete core shear wall falls into the core area.
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History And The Twin Towers Concrete Core
Oxford University in 1992 published this on the WTC concrete cores.
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What follows are the statements of various architects and engineers regarding the concrete core.
Leslie Robertson, Architect Of The World Trade Center Towers
NOTE: This link has been removed from the msnbc site and from archives several times.
http://msnbc.msn.com/id/3069641/
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.
Says engineer Robertson, “If they had fallen down immediately, the death counts would have been unimaginable,” he says. “The World Trade Center has performed admirably, and everyone involved in the project should be proud.” The buildings were designed specifically to withstand the impact of a Boeing 707, the largest plane flying in 1966, the year they broke ground on the project.
A Description of the World Trade Center
http://www.unc.edu/courses/2001fall/plan/006e/001/engineering/
The twin towers of the World Trade Center were essentially two tubes, with the north tower (1,368 feet) six feet taller than the south tower (1,362 feet), and each were 110 stories tall. Each tube contained a concrete core, which supported only the load of the central bank of elevators and stairwells (Snoonian and Czarnecki 23).
NOTE: This page has some confusion about the construction sequence of steel and concrete.
http://salwen.com/wtc
Each of the towers, in other words, was held up by its reinforced concrete core and the world's strongest curtain walls. Without the usual steel skeleton, the open floors allowed unprecedented space and flexibility. Between them, the two 1,350-foot-high towers provided 7.9 million square feet of rentable floor space, roughly the equivalent of fifty city blocks.
NOTE: This page identifies the concrete core but suffers from some confusion.
http://www.delta.tudelft.nl/archief/j33/n27/3664
NOTE: This page identifies the concrete core but does not indicate "steel reinforced core".
http://membres.lycos.fr/jcviel/BTS/sujets/2002batiment.htm
NOTE: This page identifies the concrete core from the oral history of the NYC Fire Chief.
http://www.scoop.co.nz/stories/HL0512/S00082.htm
This page identifies the concrete core in fine print on the left side. Actually a brief but accurate description.
http://www.didyouknow.org/terrorism.htm
NOTE: This page has some confusion mentioning multiple, concrete clad cores.
http://www.ussartf.org/world_trade_center_disaster.htm
This page has a brief but competent description of the concrete core
http://www.worsleyschool.net/science/files/wtc/page3.html
NOTE: This page has some confusion and relies on Snoonian and Czarnecki as do others.
http://www.unc.edu/courses/2001fall/plan/006e/001/engineering/index.html
This Page Had A Concise, Accurate Structural Description but the is now "Not Found".
http://www.blythe.org/nytransfer-subs/2001-Environment/Gallon_Environ.Letter:_Engineers_on_WTC_Collapse
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 following is a quite techinical and accurate description of all "tube construction" and the concrete core development from the beginning
http://www.911-strike.com/mitigation_of_motion.pdf
3.3 Tube Systems
One trademark of high rise construction in the late 20th century has been the use of tube systems. From the innovative designs of Fazlur Khan, developing both the bundled and braced tube concepts, tube sys- tems have served as a successful lateral load resisting system comprised of a series of closely spaced exterior columns and deep spandrel beams held rigidly together (CTBUH 1995). The use of such systems became quite popular following their introduction in landmark structures such as the Sears Tower (shown in Figure 5), World Trade Center Tow- ers, and John Hancock Center.
The concept is being continually extended in the construction of modern skyscrapers such as the Shanghai World Financial Center, (shown later in Figure 9) scheduled for completion in 2001. The design features the tube-in-tube or double tube system featuring an exterior composite tube of structural steel frame with reinforced concrete and interior tube provided by a reinforced concrete core.
August Domel, Jr., Ph.D., S.E., P.E. November 2001
NOTE: August Domel has been contacted and confirms that the concrete core is a "design method".
http://www.ncsea.com/downloads/wtcseerp.pdf
Groundbreaking for construction of the World Trade Center took place on August 5, 1966 Tower One, standing 1368 feet high, was completed in 1970, and Tower Two, at 1362 feet high, was completed in 1972. 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.
The usenet has been searched and messages by people found that describe the concrete core who saw it being constructed or knew for other reasons, the true tower core design.
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