The Collapse of World Trade Center | The Complete Physics

The terrorist attack of September 11, the enormous force of the plane's impact did not cause the Twin Towers to have a tilted fall like this, but rather the towers remained firm for more than an hour, however, to the surprise of the

world

, the towers

collapse

d like a house of cards in a vertical fall. The main reason for this strange

collapse

was the structural design of the tower, the design of the perimeter tube, the concrete floors of the World Trade Center are supported by these beams during the plane crash, the burning of jet fuel increased the temperature and caused the beams to sag, can you say what? the effect of a heavy, sunken floor on the building wait wait we are going too fast to properly understand the

physics

behind the collapse we first need to understand the geometry and design details of this building the perimeter tube design comes to life when you rearrange it from distributed columns uniformly throughout a building to a tube within a tube.

Layout of these office spaces were incredibly elegant, convenient and spacious, with no irritating columns within the office areas. This was the only reason why the engineers chose this unique perimeter tube design so that both skyscrapers would really appreciate this. Choice, let's quickly compare the layout of these offices to those found in the iconic Empire State Building, as you can see that the gigantic columns here consume a lot of usable office floor area. If you look closely, you'll notice that a single outer column does not run. Across the entire height of the tower, it is a collection of many prefabricated panels.

A single panel consists of three columns reaching three stories high. These panels are then held together by spandrel plates. Engineers connected these panels in ascending order of height repeatedly instead of taking a direct line. This method ensured good rigidity to the external columns. These cute but gigantic cranes called kangaroo cranes played an important role in speeding up the construction work of the World Trade Center. When watching this animation, can you see how this innovative crane goes up on its own? When the piston is activated, the crane increases its height. This interesting support structure that can flex only to one side helps the crane rest in this position at this stage, the bottom of the piston retracts once again.

The flexible support mechanism on one side moves inward. Action Now that the crane is properly rested it is time to attach these frames to the base to stabilize it. The way this crane goes up looks good, if you want to increase its height you simply have to repeat the same series of movements when the time comes. to assemble the frame lock neighboring kangaroo cranes provided assistance the World Trade Center towers were one of the first in the United States to use these innovative cranes did you notice what this worker is doing here? This simple technique is in fact the reason why the towers after being hit sustained for over an hour before they collapsed.

This is a spray foam insulation process. When sprayed onto a metal surface this special liquid creates a texture. Similar to foam in the event of a fire, this foam can prevent heat from reaching the steel for an hour or two depending on its ratings, this useful technique protects the building until first responders can get to the scene and control the fire. The beams and columns of the Twin Towers were covered with this spray foam insulation. Now it's time for us to explore the major second. component of the design the core, although the core occupies only 1/4 of the area, this core carries most of the gravity load of the tower, each column of the core was welded to the one below and each had a height of about 30 to 50 m later, girder beams were placed on each floor, if you zoom in and analyze the fall of the World Trade Center Tower, it is evident that what occurred was basically a sequential collapse of all its floors, let's learn something about the connection of the floors of the

world

.

Trade Center to better understand the collapse connecting the external columns and the core at a 60-foot high span was only possible through a truss arrangement the beams would have been sunk to facilitate the construction process, prefabricated portions of the floor and then struck some of the beams and secured them together by placing a steel plate over them. The beams are connected to the columns in a rather unique way. These connections of the beams were made possible through these small and crucial steel seats, the main culprit of the collapse and less mentioned in the reports offered by the government, let's take a closer look at CL.

The top chord of the truss rests on this reverse L-shaped piece of steel. This seat is then welded to the spandrel plate via these small spacer plates. Keep these connection details in mind as they play an important role. crucial role during the collapse of the towers, as we will learn later, interestingly, the knuckles of the truss were made to protrude from the steel plate so that later, when the concrete is poured, the reinforcing bars strengthen the connection to the system. of steel. Note that in this floor design the steel reinforcement is exposed with the concrete cast in place the floor of the Twin Towers is ready for luxurious open floor office spaces to run like hotcakes on top of Each tower establishes a fourth important structural element, the Hat truss.

This enormous truss structure served as a bridge between the core and the external columns. The Hat truss also provided support for an antenna on top of the tower Now that we've covered the entire structure of the World Trade Center towers, let's get into the

physics

behind their intriguing House of Cards type collapse when the hijacked plane crashed. crashed into the North Tower, broke the maze of perimeter columns up to 6 to 8 floors, this accident also damaged about 60% of the central columns, elevators and stairs were damaged. Trapping around 1,600 people on top of the tower, this shocking impact from the Boeing planes could have caused a tower collapse like this, but it didn't thanks to the strong foundation of this building and also because of the thousands of these tiny shock absorbers viscoelastic in the The construction of these rubber-based shock absorbers absorbed some of the force of the impact;

In fact, these dampers gave the towers incredible flexibility, so that on a windy day they could sway as much as 12 inches; Furthermore, the towers stood firm for more than an hour after impact, even after a huge impact. A hole was left in its columned walls. This was possible because the remaining columns, both the perimeter and the core, did a great job of supporting the weight of the building over the accident area, so if the remaining columns did such a good job, you might feel curiosity. About what exactly led to the collapse of the tower, the catalyst for the collapse was the huge temperature rise after the accident, a large amount of jet fuel burned vigorously on those 6 to 8 floors, causing a rise in temperature if the beams lacked the thermal protective layer.

As we discussed earlier in the video, the tower would have likely collapsed and in as little as 10 to 15 minutes, however, thanks to the thermal insulation spray, this was delayed for over an hour. Burning fuel caused the heat to reach a whopping 1000°C, although steel did not. If melted at 1000°C it would surely soften and would have caused the armor to sink as shown. Can you imagine what the effect would be of a sunken concrete floor in the perimeter tubes? I have two floor designs in front of me, the first one is having a straight floor and the second one is having a floor with a dip when you apply a force on the first design on the straight floor, this is actually a gravity load, no problem for the walls, they are holding firm, but if I apply the same force in the second design in the S FL design you can see that the walls are hitting inwards, which is a large deflection.

The same thing happened in the WTC perimeter design as well and this dent is so clear in some of the collapse videos, this means that the weight of the sunken concrete floor would dent the perimeter columns inside. This is due to the force acting inward. Remember that perimeter tubes also weaken due to increased temperature. Now let's see what the effect of a dent is on the design of a perimeter tube. A simple can is equivalent to a perimeter tube design. Surprisingly, such a small can is able to support the weight of three large ones, but if you add a small dent in the can, it just collapses and if you check the details, oh my goodness, it was a perfect vertical. collapse, you can see the same thing happened in the WTC perimeter design and similar to the experiment when an axial force passes through a perimeter tube designed with a dent, it simply collapses in the region of the dent, this is a clear case of buckling.

We have probably all experienced or at least seen buckling. Buckling occurs when a compression load acts axially on a thin beam due to buckling. The buckling occurred with a much lower load. Can the strong central core prevent the upper floors from falling? Unfortunately, no, you can't. We have already seen how the floors are loosely connected to the core; Furthermore, due to the high temperature, these connections were further weakened during the collapse of the floors due to the dent, the core support would simply break with almost no connection to the core. It is clear that the collapse of all the upper floors downwards, the mass of the upper 15 floors was equivalent to that of the Titanic, reaching a mind-blowing 38,000 tons, in addition, the Hat frame and the Boeing also fell in the Sudden Impact due to their The weight on the floor just below shattered the lower floors, the perimeter tubes also bent almost immediately as the force of the impact was enormous and compressive in nature, this caused an unfortunate chain reaction and one by one the floors continued to collapse. , the weight also continued to increase as the building collapsed.

Seeing the images of the tragedy, you must surely have seen the destruction of the perimeter columns during the collapse. This was due to buckling. The North Tower collapsed in 13 seconds and the South Tower took only 11 seconds. Did you know this exact scenario was? Tested before the towers were built in the plane crash test, this tower design held up quite well, however, the engineers did not consider two conditions: one was the burning of the jet fuel gallons and the second was the size of the aircraft at the time of testing. The largest plane engineers considered was the Boeing 707, which was half the size of the one that actually crashed The One World Trade Center Tower that was erected in The Honorable Position of the Twins consists of measures to improve rescue strategies and the thermal design of the building in At One World Center, engineers built a thick reinforced concrete wall surrounding the exit stairs.

This thick concrete wall acts as the core of the building for obvious reasons. They moved away from the steel core design during a plane crash. The concrete core will remain strong regarding This time the floors did not expose any steel structure and chose to cover it

complete

ly with concrete, this prevents any possibility of the steel structure of the floor collapsing due to the rise in temperature. The government also introduced many new regulations for construction safety with these new safety standards. measures implemented the new World Trade Center is the tallest building in the Western Hemisphere now that you understand the physics of collapse well here is an interesting question for you after being hit, the North Tower stood firm for 1 hour and 42 minutes before collapsing However, the South Tower collapsed in only 56 minutes, what could be the reason for this time difference?

The reason is the weight of the floors on the accident region. The South Tower accident occurred 14 stories lower than the North Tower, which means that the South Tower had to bear a much greater load during the time of fuel consumption, this would obviously lead to easy buckling. This is why even if the North Tower were hit first, it would collapse second, usually during a fire accident, stairs play an important role in evacuating occupants; However, in this case the stairs could only save a few people, this was mainly because most of the stairs were blocked by plaster debris.

Additionally, all staircases were located in the central area, with the South Tower staircase reportedly being the only one that was usable for many years. people compare the Empire State Building accident of 1945 to the 9/11 attack which the Empire State survived but theWorld Trade Center no. The reality is that these two events are simply incomparable when considering the size of the plane involved in the accident. The State Building incident was a small bomber plane, while the World Trade Center was hit by a gigantic passenger plane. The care the engineers took while building the foundations of the Twin Towers was incredible.

A strange concrete wall can be seen inside the ground and around the building. known as a diaphragm wall and its main function is to prevent water intrusion from the nearby Hudson River. Look at the way they have reinforced the concrete walls using tie cables. Engineers were able to locate strong bedrock at a depth of seven stories of concrete. The foundation of this building progressed from there, engineers called this new foundation technology a bathtub. Interestingly, the foundation of the bathtub also housed two tunnels. This strong foundation was the main reason why the impact force of such a gigantic plane could not bring down the building.

The Twin Towers may not have collapsed if the terrorist had attacked the building, say five floors above the actual impact site or if instead of a perimeter tube design a normal steel skeleton column design had been used, too It could have been avoided if engineers had used a strong joint in place. Floor core connection, even the terrorists behind the attack probably couldn't have imagined all the physics that happened after the plane crash or even anticipated a collapse of such a monumental building. Sometimes physics is cruel, you can see the enormous amount of rubble that formed after the collapse of Tin Towers surprisingly when they cleaned the rubble you can see a column that remains strong and brave.

This is a column of the central core of the building. I know this even after all the scientific explanation about the collapse. I will be able to read in the comments section what happens with the wtc7 Tower. It collapsed even if the plane did not touch it. There is a scientific explanation for that too, but not in this video. This video is only 15 minutes long. Give me a week's time, we'll cover that part too now on this Brave column. It is currently moved to a museum, a museum dedicated to the WTC Memorial and this column still stands firmly there, but if you want to see this canal, stay strong. please support us on patreon we are not doing well financially waiting for your support take care goodbye