The only core of the Twin towers that can be proven with evidence, is the concrete core.
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 outside 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 deformation of shear walls failures occur. These were facts 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" to S. Jones from Silverstein and Associates. 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 structure. 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. Also a third wall in the center crossing the narrow axis.
Twin Tower Hat Truss
Both towers were high performance structures having a hat truss to transfer loads from one side of the towers steel exterior framework to the opposite side. The vertical distribution of loads on the inner wall of the exterior steel frame was via moment frames of the interior box columns which had a surcharged fastening schedule of 10 floors of concrete over the fastening point before fastening was allowed. Distributing the 20% over the vertical dimension of the core. The hat truss was bearing upon the top edge of the concrete core acting to couple it, via truss, to the moment frames.
A hat truss bearing on a material similar to that which it is meant to brace, suffers from the same flexibility that the structure it is trying to brace. The presence of the inner concrete tube of the Twin Towers, of the tube in a tube design, increased the performance of the hat truss because the concrete did not compress and flex compared to the steel.
It is unknown if the hat truss extended to the perimeter columns because photos do not show that phase. It is illogical because the floors acting as diaphrams in compression or tension, depending on wind, would transfer loads vertically accumulated over the towers faces to distribute them horizontally by transmitting them to the moment frames of the inner steel framed wall of interior box columns. The hat truss distributed the horizontal forces after converting them to vertical forces to the concrete core and the moment frame on the opposite side of the tower.
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, cast concrete reinforced with custom high tensile steel rebar was the strongest possible design and both WTC 7 and the new Freedom tower are to be built in this way. 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.
Below I've crudely altered an earlier FEMA core diagram to show how the concrete core, interior walls and hallways were configured through the entire height of the 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.
From communicating to people who worked above the 90th floor, the hallways went both directions on a single floor; from this it seems that the weakening of the towers shear walls that the hall doorway openings caused, was not a problem near the top, so the hallway/door scheme was changed higher up.
The south tower was different, 2 hallways crossed the core in both directions. The south tower core was not tapered as it was not strictly shear wall design. Ascending series of 3-4 floors stepped their dimensions smaller and smaller. Floors and a full height central wall across the short axis were combined into a semi cellular configuration termed "super core", a combined cell/shear design.
The hallway/door scheme was changed higher up. See the page Understanding The Silhouetted Images Of The Twin Towers for more detail.
The hallway floors of the core were primarily joisted with steel but had walls one floor in height providing additional support and resistence to the floor diaphrams compressing the core wall faces. Those interupted walls alternated with the every-other floor hallways below the 43rd floor.
North Tower Core
The core wall faces were formed with flat surfaces on a very slight taper.
South Tower Core Design
In the crude diagram below the scale is inadequate to show the overlap of the core hall floors onto the vertical face of the inside of the core walls. Extensive joining of reinforcing steel in these places completed the cell/shear wall configuration.
The core wall thickness of WTC 2 changed in stepping at perhaps 4 floor intervals below the 43rd, above that the sides were parallel.
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?
WTC 2 CONCRETE CORE STANDING
A few seconds later, the core has lowered a hundred feet or so.
The core shown on the FEMA site will not leave a spire standing like we see below. No visible multiple, heavy steel core columns are seen in photos. The core is always empty. No part of a steel columned core could have this appearance as it is halfway to the ground Above.
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. There is an edge of the hall door on the left, as it is only one corner from the hall edge outwards.
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.
purple arrow is a portion of perimeter wall trapped
under the falling concrete.
The purple arrow is a portion of perimeter wall trapped under the falling concrete.
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.
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 (spire location page) above are larger than the steel columns the core was supposedly made from. There were 24 and they were hand fabricated in 40 foot sections then 100% welded in place. The below photo was taken at very close to the same distance as the one above.
Below are a long row of 3" rebar on 4 foot centers seen at approximately 7500 feet.
The 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 across the walls of the core. Slopes ran in opposite directions on opposite sides maximizing torsion resistance of the tube. The slope of the tops of the rebar in the photo above show this same slope.
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.
The slope to the top of the rebar was mentioned in the documentary, "The Engineering and Construction of the Twin Towers".
Dr, Ron Larsen, Ph.d, physics and a former Marine Major conducted a search for the documentary. This is a link to an edited .mp3 of his web radio show "Liberty Calling", which I co-hosted for a time with Dr. Larsen. The few minutes he discussed the search for the documentary has been extracted in the shorter version. To get the full 1 hour, the .mp3 file can be downloaded here.
interview (documentary search update 17:50 minutes)
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.
Below is an animation taken from this video
WTC North Tower Core, HAVE YOU SEEN IT?
9/11 WTC North Tower Core, HAVE YOU SEEN IT?
showing large pieces of concrete falling from the east WTC 1 core wall position.
Here is a still from a helicopter of the same triangular piece of the WTC 1 concrete shear wall falling into the core area.
ELEVATOR GUIDE RAILS FALLING
The images and video below is at about the same moment but taken from the north west.
Above is the formation of the spire an interior box columns located outside the concrete core walls. A fragment of the concrete shear wall can be seen still attached to what are elevator guide rail support steel falling out of the plane of the core wall and interior box columns. They are identified by the lack of horizontal stubs of floor beams attached to them as the spire to the right has.
North Tower "Collapse" (new video)
9/11: North Tower "Collapse" (new video)
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.
See the "SPIRE SEQUENCE" page for more detail.
And left the rebar of the core, delaminated from the concrete, standing for a few short seconds as seen below.
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. The foundation of the core had 6 inch high tensile steel rebar and some extended up through the base walls into the tapering core wall.
An approximate 3x7 foot utility access hallway running the length of the north side core wall shows daylight through from behind the core remnant.
Below is a screen shot of A-A -24 available here.
The plan from Silverstein shows a steam shaft air shaft and a janitors closet where the concrete wall with utility wall above is seen. It is an obsolete plan used to mislead the truth movement.
The below image shows the elevator guide rail that was footed on "grillage" which had toppled over onto the pile or on the right side of the photo immediately above at an earlier stage of the cleanup. Note there are no gusset plates which would be required if the vertical steel were core columns. No diagonal braces are seen also. The concrete core provided, via its shear walls, all diagonal/lateral support for the tower so elevator doors and hallways were uninterrupted by diagonal braces.
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.
History And The Twin Towers Concrete Core
Oxford University in 1992 published this on the WTC concrete cores.
What follows are the statements of various architects and engineers regarding the concrete core.
Leslie Robertson, Architect Of The World Trade Center Towers
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.
http://msnbc.msn.com/id/3069641/ (Note: ARCHIVE-Original page redirected July 2010 to new misinfo)
A Description of the World Trade Center
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.
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.
NOTE: This page identifies the concrete core but does not indicate "steel reinforced core".
NOTE: This page identifies the concrete core from the oral history of the NYC Fire Chief.
This page identifies the concrete core in fine print on the left side. Actually a brief but accurate description.
NOTE: This page has some confusion mentioning multiple, concrete clad cores.
This page has a brief but competent description of the concrete core
NOTE: This page has some confusion and relies on Snoonian and Czarnecki as do others.
This Page Has A Concise, Accurate Structural Description
heart of the structure was a vertical steel and concrete core, housing
lift shafts and stairwells. Steel beams radiate outwards and connect
uprights, forming the building's outer wall.
August Domel, Jr., Ph.D., S.E., P.E. November 2001 (Chapter 2.1)
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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