WTC wide view

With its pride, the World Trade Center Twin Towers - World Trade Center (WTC) in New York shocked everyone who knew it during the November 9, 2001 event. because the plane crashed, exploded, burned and when it collapsed, within 10 seconds the building was only a mountain of debris. The main factor causing the building to collapse is still a topic that has not been agreed by scientists until now. But most of the comments mention the following points:

STRUCTURE

The construction of the WTC twin towers began in the mid-sixties to the early seventies of the last century. This is a breakthrough in the construction of high-rise buildings with lightweight materials and modular structures to reduce construction costs and construction time.

WTC Twin Towers as two pillars plugged into the ground 21m on a square cross-section 64m, 411m high above the ground. The weight of each of these pillars is about 500,000 tons. In fact, its own weight is not the main load that the tower has to bear, but the horizontal thrust due to the wind.

Located on the Atlantic coast, New York region suffers from massive storms with wind speeds up to 225km / g. Hence the buildings here are twice as resilient to those in earthquake zones. WTC alone withstands wind pressure up to 200kg / m2 equivalent to a force of 5,000 tons impacted from one side into the building.

Floor beams are hung up on columns and core

The two towers have a tubular structure consisting of 244 square 360mm steel columns surrounding a core with a cross section of 27m x 40m. This core also has a framework of steel structures designed to bear the load of the building. The enclosed columns are linked to the core by steel beams 800mm high. On these steel beams are the beton floors of the floors. In fact, this link looks loose because the 800 beam is almost always resting one end on one pillow on the casing column and the other end on one pillow on the core of the tower. Thus the tower is like a crate with more than 90% empty volume. That is proven when collapsed down the tower is only a pile of debris several floors high. Even so, the building will remain stable in the event of a few pillars being damaged. The adjacent columns will then carry the load of the damaged column.

PLANE CRASHED

FIRE

Many people thought the flames melted or softened the steel leading to the building's demise. It is understandable because the terrible flames of 90,000 liters of jet fuel completely cover part of the towers. But actually, a big fire does not necessarily have a high temperature. The flame in this event is a diffuse fire which means that fuel and oxygen are not mixed prior to the fire, but gasoline shoots into the air and ignites when the rate of ignition is reached. This is a flame for the lowest temperature of all types of combustion reactions, because when burning, in addition to the heat that heats the carbonic molecules and water to the fire, it also has to transfer heat to the nitrogen molecules in the air and to the molecules Gasoline death does not burn. Under such fire conditions, the flame that collapses the WTC is only about 500 ° C to 650 ° C. It is far from reaching the temperature of softening and melting. At this temperature, steel is reduced by 50% in strength. But with a structure to resist heavy storms like the WTC twin towers, on that windless day steel structures were only 1/3 of the maximum load even at 650 ° C.

DRAWING DOWN

Closer attention to the structure of the tower will easily see the weakest points in the structural system are the girder supports on the floor beams and the core. Expansion of the supporting beams in floors with high temperature will push the arched column outward, causing the girder supports of the upper story to be destroyed and the concrete floor collapses. The floor below, which is also deformed, is subjected to an additional load of the floor that just collapsed.

Steel structure deformed due to fire

This phenomenon occurs in the layer with high heat and has the most deformation. As a result, the growing mass of the burned floors collapsed onto the floors below. The large volume coupled with close inertia close to free fall causes the layers below to quickly join the plunging block of beton like a chain reaction. And in just 10 seconds this reaction ended and also ended the once proud American mighty and ushered in a new kind of hatred and violence.

Live, Freedom and Hunt All Threats	Prow from WTC scrap steel