On the morning of Tuesday 11 September 2001, two scheduled planes, belonging to the major American airlines (United Airlines and American Airlines) were diverted by a group of terrorists belonging to the terrorist organization Al Qaeda. The American Airlines 11 flight and the United Airlines 175 flight were respectively crashed on the north tower and the south tower of the World Trade Center, in the Lower Mantthan neighborhood in New York. Within 1 hour and 42 minutes, both twin towers collapsed. This attack, together with two other hijacations that took place on the same day, caused the death of almost 3,000 people. Today, to commemorate the memory of the fallen of 11 September, at the exact point of the tragedy stands the National September 11 Memorial & Museum or “Ground Zero” – literally “zero level”. Built on the foundations of the towers, it has different areas including the Plaza Memorial, a space with two huge tanks 9 meters high (30 feet) which follow the perimeter of the towers, equipped with artificial waterfalls and bordered by bronze panels with the names of the victims engraved. Below the memorial is the museum, which houses numerous symbolic finds, including the “Last Column” and the remains of a fire truck.
The National September 11 Memorial & Museum in Ground Zero
The National Septeber 11 Memorial & Museum is a complex that makes tribute to the memory of the over 2900 deaths of the attacks of 11 September, and those of the attack on February 1993. The site where the memorial was created is called Ground Zero. The term derives from military jargon, and indicates the exact point where a bomb, in particular a nuclear bomb, explodes. The choice to use this name to indicate such a place is aimed precisely at transposing the sense of tragedy of events and devastation.
The project consists of different areas, or sectors. The Memorial Plaza, created according to the Michael Arad and Peter Walke project, was created instead of the foundations of the twin towers, is an area of 8 acres (3,237 hectares) on which 400 oak trees were planted. The outdoor memorial was designed to offer a silent space, aimed at contemplation. At the center of the memorial there are two huge tanks, whose perimeter is exactly the one occupied by the two towers, each of which occupies an area of almost 1 hectare. The two swimming pools have been conceived and make in order to host the largest artificial waterfalls in America. These are two voracies 9 meters high, on whose edges are carved names of the 2977 victims of 90 different nationalities. We wanted to give the impression that the water would fall into the void, without ever stopping. This requested the adoption of a complex water collection and drainage system, including a face heating system and prevent the water from fulfilling the colder months.
One of the most particular, and certainly commemorative elements is certainly Survivor Tree. It is a tree of Pero that has been recovered by the rubble, treated and made growing, and planted in the memorial, to symbolize the resilience of the American people towards such vile attacks.
The 9/11 Museum
The Museum of Attacks of 11 September was built under the memorial. Inside the museum there are many deeply symbolic objects. One of the most important “Last Column”, the last pillar removed from the place of attacks, together with a destroyed fire truck. Another interesting engineering element is the “Slurry Wall”, an reinforced concrete wall that avoided that the site was flooded during the flooding of the Hudson river. This wall was already part of the World Trade Center complex and was “recovered” as an integral part of the museum.
Among the main challenges that the engineers faced in the construction of the museum. The space available was little, and the engineers also found themselves having to face the presence of other important infrastructure elements such as the subway right at the point where the entrance should have been made. This led the designers to choose to support the entire structural deck in just 12 points, exploiting the roof of the museum as a side support.
In this place, every year, the American government organizes commemorative events, aimed at not making the memory of the attacks lose and to explain to the youngest what was 11 September.
The twin towers
The attacks on the World Trade Center were perpetrated against the two major towers of the entire WTC complex, made up of 16 towers, mostly designed by the architect Minoru Yamasaki and engineer Leslie Robertson. The two towers were, in fact, the symbol of the WTC, and were inaugurated on April 4, 1973.
At the time of their completion, the two towers were the highest constructions in the world, with their 417.5 m the north tower, and 415 m the south tower. The total surface of both towers was 800,000 square meters, and the two towers had a total of 196 elevators.
