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 mis 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 north through the line of the north perimeter wall of WTC 1 from just west or perhaps still inside the tower core footprint.
WTC 2 CONCRETE CORE STANDING
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/
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).http://www.unc.edu/courses/2001fall/plan/0...01/engineering/
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.http://salwen.com/wtc
This Page Has A Concise, Accurate Structural Descriptionhttp://www.blythe.org/nytransfer-subs/2001...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.
August Domel, Jr., Ph.D., S.E., P.E. November 2001
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.http://www.ncsea.com/downloads/wtcseerp.pdf
NOTE: The link for the following does not respond. 2/06/06
The World Trade Center towers were an unusual design, at least at the time they were built. Their support structure is called a 'bundled tube', or in engineering terms, a glass curtain wall structure. What this means is that the buildings are tubes, made rigid by a lattice of steel beams on the outside walls. These vertical columns are strengthened by horizontal beams, and this design is what helps support the building, and keep it stable in high winds. An inner concrete core houses the elevators, and provides additional vertical load supporthttp://www.ncusd203.org/central/html/what/...tc/graphic.html
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.http://cosmicpenguin.com/911/chrisbrown/corerefs/index.html