When was world trade center built

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.

Two months after the release of the blockbuster movie The Towering Inferno , a three-alarm blaze in the North Tower in raised concerns that the Twin Towers had no sprinklers. But the sprinklers failed when they were needed the most. On the morning of August 7, , French acrobat Philippe Petit walked the more than feet between the Twin Towers on a high wire approximately one-quarter mile up in the air.

Fire reserve water tanks provide twice the required storage capacity and connect to two standpipes that serve alternating floors. This creates secondary protection in the automatic sprinklers if any standpipes are compromised. The sprinkler system is also designed with higher than required capacity. Stairwells are pressurised to lessen smoke infiltration and oversized at landings to accommodate the disabled and stage emergency equipment.

Stairs and standpipes are entirely encased in separate fire-rated enclosures of reinforced concrete to provide a high level of protection for exiting occupants and fire suppression systems. Photo-luminescent materials and paints guide people along exit routes and stairs. They are also used for directional signs in the event that lighting becomes obscured, with additional photo-luminescent exit signs and path indicators installed just above the floor to assist occupants impeded by smoke.

Exit signs and lighting systems have battery backup in addition to the required connection to emergency power. To improve emergency responder communications, an internal antennae and repeater system in the stairwells enhances the communication capabilities of emergency personnel.

A fire command centre on the ground floor contains an alarm system with a separate, redundant communication backbone. The smoke exhaust system purges three floors simultaneously, exceeding requirements. To reduce the potential of contaminated outside air being introduced, outside air systems and fresh air intakes for emergency generators are located at the top of the building.

Fuel oil tanks for emergency generators are located outside the footprint of the building under a neighboring plaza. At a height of 1,ft m , the….

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Web joists 80 cm tall connected the core to the perimeter at each story. Concrete slabs were poured over these joists to form the floors. In essence, the building is an egg-crate construction that is about 95 percent air, explaining why the rubble after the collapse was only a few stories high.

The egg-crate construction made a redundant structure i. Prior to the World Trade Center with its lightweight perimeter tube design, most tall buildings contained huge columns on 5 m centers and contained massive amounts of masonry carrying some of the structural load. The early news reports noted how well the towers withstood the initial impact of the aircraft; however, when one recognizes that the buildings had more than 1, times the mass of the aircraft and had been designed to resist steady wind loads of 30 times the weight of the aircraft, this ability to withstand the initial impact is hardly surprising.

The only individual metal component of the aircraft that is comparable in strength to the box perimeter columns of the WTC is the keel beam at the bottom of the aircraft fuselage. While the aircraft impact undoubtedly destroyed several columns in the WTC perimeter wall, the number of columns lost on the initial impact was not large and the loads were shifted to remaining columns in this highly redundant structure.

The ensuing fire was clearly the principal cause of the collapse Figure 4. The fire is the most misunderstood part of the WTC collapse. Even today, the media report and many scientists believe that the steel melted. It is argued that the jet fuel burns very hot, especially with so much fuel present. This is not true. Part of the problem is that people including engineers often confuse temperature and heat. While they are related, they are not the same. Thermodynamically, the heat contained in a material is related to the temperature through the heat capacity and the density or mass.

Temperature is defined as an intensive property, meaning that it does not vary with the quantity of material, while the heat is an extensive property, which does vary with the amount of material.

One way to distinguish the two is to note that if a second log is added to the fireplace, the temperature does not double; it stays roughly the same, but the size of the fire or the length of time the fire burns, or a combination of the two, doubles.

Thus, the fact that there were 90, L of jet fuel on a few floors of the WTC does not mean that this was an unusually hot fire. The temperature of the fire at the WTC was not unusual, and it was most definitely not capable of melting steel. In combustion science, there are three basic types of flames, namely, a jet burner, a pre-mixed flame, and a diffuse flame. A jet burner generally involves mixing the fuel and the oxidant in nearly stoichiometric proportions and igniting the mixture in a constant-volume chamber.

Since the combustion products cannot expand in the constant-volume chamber, they exit the chamber as a very high velocity, fully combusted, jet. This is what occurs in a jet engine, and this is the flame type that generates the most intense heat. In a pre-mixed flame, the same nearly stoichiometric mixture is ignited as it exits a nozzle, under constant pressure conditions.

It does not attain the flame velocities of a jet burner. An oxyacetylene torch or a Bunsen burner is a pre-mixed flame. A fireplace flame is a diffuse flame burning in air, as was the WTC fire. Diffuse flames generate the lowest heat intensities of the three flame types. If the fuel and the oxidant start at ambient temperature, a maximum flame temperature can be defined. This maximum flame temperature is reduced by two-thirds if air is used rather than pure oxygen. The reason is that every molecule of oxygen releases the heat of formation of a molecule of carbon monoxide and a molecule of water.

If pure oxygen is used, this heat only needs to heat two molecules carbon monoxide and water , while with air, these two molecules must be heated plus four molecules of nitrogen. Thus, burning hydrocarbons in air produces only one-third the temperature increase as burning in pure oxygen because three times as many molecules must be heated when air is used.

But it is very difficult to reach this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio. Typically, diffuse flames are fuel rich, meaning that the excess fuel molecules, which are unburned, must also be heated. This fuel-rich diffuse flame can drop the temperature by up to a factor of two again. Some reports suggest that the aluminum from the aircraft ignited, creating very high temperatures.

While it is possible to ignite aluminum under special conditions, such conditions are not commonly attained in a hydrocarbon-based diffuse flame. In addition, the flame would be white hot, like a giant sparkler. There was no evidence of such aluminum ignition, which would have been visible even through the dense soot.