World Trade Center Twin Towers     With its pride, the World Trade Center Twin Towers - World Trade Center (WTC) in New York shocked everyone who knew it during the events of November 9, 2001. Everyone knows that it was caused by a plane crashing into it, exploding, burning, and when it collapsed, within 10 seconds the building was just a mountain of rubble. The main factor that caused the building to collapse is still a topic that has not yet been agreed upon by scientists. But most comments mention the following points: Damage caused by aircraft impact. □ The fire destroyed the building. □ Sudden collapse of the legs.   STRUCTURE The WTC Twin Towers were built starting in the mid-sixties to early seventies of the last century. This is a breakthrough in high-rise building construction using lightweight materials and modular structures to cut costs and construction time. The WTC Twin Towers are like two pillars inserted 21m into the ground on a square section of side 64m, 411m high above the ground. The weight of each of these pillars is about 500,000 tons. Actually, self-weight is not the main load that the tower must bear, but the horizontal thrust due to the wind. Located on the Atlantic coast, the New York region is subject to major storms with wind speeds of up to 225km/h. Therefore, buildings here can withstand twice as much as buildings in earthquake zones. WTC alone can withstand wind pressure of up to 200kg/m2, equivalent to a force of 5,000 tons acting on the building from one side.   Floor beams are mounted on cover and core columns   The two towers have a tubular structure consisting of 244 360mm square steel columns surrounding a core with a cross section of 27m x 40m. This core also has a steel structural frame designed to bear the load of the building. The columns are connected to the core by 800mm high steel beams. Above these steel beams are the concrete floors of the floors. In fact, this connection looks loose because the 800 beam almost only rests one end on a bearing on the cover column and the other end on a bearing on the tower core. Therefore, the tower is like a basket with more than 90% empty volume. That was proven when the tower collapsed and was reduced to a pile of debris several stories high. However, the building will still stand in case a few columns are damaged. At that time, the adjacent columns will bear the load of the failed column.