Opposition to lateral motion is controlled by "the design's structural mass [weight], the stiffness of its lateral members and the degree of structural damping employed," Fowler said. He calculated that the approximate maximum wind shear force that a single face needed to withstand to be somewhere around 11,, pounds. The gravity loads weight produced by the towers at their bases were on the order of , tons, Fowler said.
To handle these immense forces, the engineers "designed the World Trade Center essentially as a large beam section," explained another panel member, Robert McNamara, president of the engineering firm McNamara and Salvia. Called structural tubes in the business, each twin tower was strongly framed in structural steel. The frame comprised inner and outer rectangular box tubes consisting of closely spaced steel box columns connected by steel spandrel members or truss beams that supported 40,square-foot cross-braced floors, each nearly an acre in area, the empaneled engineers said.
This configuration created a complete exterior tube around the building and a center tube down the middle. The foot-long central core, formed of massive vertical steel columns that held most of the building's weight, contained elevator shafts, stairways and utility spaces, they said. The core's columns were thicker toward the base to support huge accumulated gravity loads. The outer perimeter tube, a tight prefabricated latticework with 61 inch steel box columns spaced 39 inches on center on each building face, provided all the bracing resistance against lateral and twisting forces from wind and seismic action.
This exterior grid served as a moment frame, providing a large moment arm of torque against overturning and deflection forces. The outer tube bore part of the gravity-induced downward load as well as, they noted.
The huge inner and outer rectangular tubes "needed to be protected to maintain their structural integrity, so the floors acted as reinforcing diaphragms or bulkheads [the term used in shipbuilding]," said panel member Jerome Connor, professor of civil and environmental engineering at M. The office floors, which each comprised a to foot clear span from the core to the exterior grid, were panelized structural members supported by open web joists with steel decks above them, he said.
The horizontal truss struts, bolted and welded to the exterior grid and the core column structures, included viscoelastic stringers that provided increased damping to help make the structure less lively in the wind, according to Connor. Each steel floor deck was covered with four inches of concrete.
After the deletion of key structural members from about the 90th to 96th floors on the north face of the north tower, One WTC, and from about the 75th to the 84th floors of the south, east and north faces of the south tower, Two WTC, the buildings' skeletons found alternative paths to take the loads. Each impact and following explosion imparted first a large local lateral force and then an omnidirectional force to the structures, together causing massive initial damage to the columns and floor systems at the elevation of the crash.
Despite shocks and explosions estimated to be equivalent to that of the truck bombing of the Alfred P. It's a testament to the system that they lasted so long. The events of September 11th show that this was indeed the case. The towers collapsed only after the kerosene fuel fire compromised the integrity of their structural tubes: One WTC lasted for minutes, whereas Two WTC remained standing for 47 minutes.
The aviation fuel fires that broke out burned at a much hotter temperature than the typical contents of an office. Some have raised questions about the degree of fire protection available to guard the structural steel. According to press reports, the original asbestos cementitious fireproofing applied to the steel framework of the north tower and the lower 30 stories of the south were removed after the terrorist truck bombing.
Others have pointed out the possibility that the aviation fuel fires burned sufficiently hot to melt and ignite the airliners' aluminum airframe structures. Aluminum, a pyrophoric metal, could have added to the conflagrations. Hot molten aluminum, suggests one well-informed correspondent, could have seeped down into the floor systems, doing significant damage.
The goblets are white hot, burning at an estimated degrees Celsius. At this temperature, the water of hydration in the concrete is vaporized and consumed by the aluminum. This evolves hydrogen gas that burns.
This keeps the metal hot and burning. If you look at pictures of Iraqi aircraft destroyed in their concrete shelters [during the Persian Gulf war], you will notice a deep imprint of the burned aircraft on the concrete floor. Though the Boeing s airliners that hit the towers were somewhat larger than the Boeing maximum takeoff weights: , pounds versus , pounds the structures were designed to resist, the planes carried a similarly sized fuel load as the older modelabout 24, gallons versus 23, gallons, according to Kausel.
When released, the accumulated potential energy is converted to kinetic energy. With a mass of about , tons 5 x 10 8 kilograms , a height of about 1, ft. The M. The huge gray dust clouds that covered lower Manhattan after the collapse were probably formed when the concrete floors were pulverized in the fall and then jetted into the surrounding neighborhood.
The towers were completed in The towers' design featured a distinctive steel-cage exterior consisting of 59 precise, narrowly spaced slender steel columns per side.
An architect's model of the proposed World Trade Center, c. Project managers faced cost overruns as safety, wind and fire tests were conducted. And engineers embraced or created innovative construction techniques and new technologies to make the towers lighter and taller. To build such tall towers on landfill that had piled up onto Lower Manhattan for centuries, the towers needed exceedingly strong foundations. So engineers dug a huge rectangular hole seven stories down into the soft soil to reach bedrock.
But it worked like a bathtub in reverse. The 1. The Twin Towers had elevators operating inside 15 miles of elevator shafts, and when they were installed, their motors were the largest in the world. That innovation lessened the amount of space the elevators took, leaving more rentable floor space.
Engineers concluded in wind tunnel tests in that the towers could sustain a thrashing of m. But they also realized that in the winds coming off the harbor, the towers could sway as much as 10 feet, making office space potentially tough to rent. One hundred days after the suicide attacks that brought down the twin towers of the World Trade Centre and killed nearly 3, people, the final fires have stopped burning at Ground Zero.
With the MISR data, Kahn calculated the height of the plume, composed of sub-visible aerosols, to be 1. Begin typing your search term above and press enter to search. Press ESC to cancel. Ben Davis August 11, What were the dimensions of the World Trade Center? How tall were the twin towers of the World Trade Center? What was the length and width of the twin towers? How far apart were the World Trade Centers?
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