To solve the problem of wind sway or vibration in the construction of the towers, chief engineer Leslie Robertson took a then unusual approach — instead of bracing the buildings corner-to-corner or using internal walls, the towers were essentially hollow steel tubes surrounding a strong central core. The 208 feet (63.4 m) wide facade was, in effect, a prefabricated steel lattice, with columns on 39 inch (100 cm) centers acting as wind bracing to resist all overturning forces; the central core took the majority of the gravity loads of the building. A very light, economical structure was built by keeping the wind bracing in the most efficient area, the outside surface of the building, thus not transferring the forces through the floor membrane to the core, as in most curtain-wall structures. The core supported the weight of the entire building and the outer shell containing 240 vertical steel columns called Vierendeel trusses around the outside of the building, which were bound to each other using ordinary steel trusses. In addition, 10,000 dampers were included in the structure. With a strong shell and core such as this, the exterior walls could be simply light steel and concrete. With the massive core and lightweight shell for structural integrity, Robertson created a tower that was extremely light for its size. This method of construction also meant that the twin towers had high load-bearing walls.

Construction

1 World Trade Center and 2 World Trade Center under construction; Empire State Building and PanAm Building seen in Midtown, 1970
1 World Trade Center and 2 World Trade Center under construction; Empire State Building and PanAm Building seen in Midtown, 1970

Groundbreaking for the construction of the World Trade Center was on August 5, 1966. The construction was under the auspices of the semiautonomous Port Authority of New York and New Jersey. Thirteen square blocks of low rise buildings in Radio Row, some of which predated the American Civil War, were razed to clear the site for construction.

The excavation of the foundations of the WTC complex, known as the Bathtub, was particularly complicated since there were two subway tubes close by needing protection without service interruption. A six-level basement was built in the foundations. The excavation of about 1 million cubic yards (760,000 m³) of earth and rock created a $90 million real estate asset for the project owner, the Port Authority of New York and New Jersey, which helped offset the enormous loss in revenues which came from the tax breaks given to the Trade Center itself. The soil was used to create 23 acres (93,000 m²) of landfill in the Hudson River next to the World Trade Center site, which became the site of Battery Park City (still under development).

In 1970, construction was completed on One World Trade Center, with its first tenants moving into the building in December 1970. Tenants first moved into Two World Trade Center in January 1972. When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million. The ribbon cutting ceremony was on April 4, 1973.

View Looking East. North Tower is on Left

Above 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.

Building WTC7 

Housed all the Enron investigation records (and other companies under investigation)...  don't hear much about Enron since. The small office fires that supposedly were the cause of the fall of WTC 7 just happened to be in the offices that held those investigations

Pentagon

The Pentagon wing that was 'hit' is 'rumored' to have held the investigation records for the 3.5 TRILLION dollars that were announced missing on 910... by Rumsfeld... it was also under construction at the time so not many people in that section

Next day we forgot all about that and listened to Bush ask for more billions to carpet bomb the desert..

Gasoline jacked up... due to the war... despite we NEVER bought oil from Iraq... and despite the fact that OPEC was scared and reduced price per barrel

Exxon reports record EVER quarter profits in the first year of the war

CBS NEWS
9/10/2001: Rumsfeld says $2.3 TRILLION Missing from Pentagon
Pentagon admits $2.3 Trillion missing and Rumsfeld calls it a matter of "life and death."

Much has been said about the fires caused by the burning jet fuel, hot enough to 'soften' the steel girders in the central columns. Meet Edna Cintron ( RIP Edna)