With the number of 9/11 conspiracy theory diaries being posted and the repitition of the same conspiracy questions a suggestion was made that we should put together some links to help respond to them.
So here goes. A discussion of building implosion that can be used to debunk WT7 conspiracy theory is on the flip.
Disclaimers first. I'm not a certified structural engineer, although I have studied some basics as part of my work in the contruction industry. I have had an interest in building implosions for many years and have read every bit of information I can find about the subject. Anyone with experience in implosions or structural engineering please comment as needed.
First of all the basic idea of structure needs to be understood. Any building is a compromise of strength and cost. You can always make a building stronger, but then it will cost more. So the engineer has to design a building to a certain set of constraints, with a safety factor to allow for the unexpected.
Anything-anything at all-that is not lying on the ground is counteracting the force of gravity in some way. In the structure of a building the force of gravity is counteracted by compression and tension in the columns and beams of the building. Weight of the building itself and it's internal loads is carried to the ground through vertical columns, while the floors are supported by beams connected to the columns. The beams also keep the columns from tipping over.
Think of a 2x4 sitting flat between two concrete blocks about 10 feet apart. Stand on the 2x4 like that and it will bend in the middle. This is called deflection. Set the 2x4 on edge and stand on it again and it will deflect less. Replace it with a 2x12 and stand on it and it will hardly deflect at all. This works for steel structures as well. When you walk across the floor of a steel framed building the beams do deflect, but in such a small amount that it is difficult to measure.
Normally the engineer has designed the building to support many people walking across the floor along with all kinds of funishings sitting on the floor at all times. The design is such that the deflection is absolutely unnoticable-in fact you would need equipment much more sensitive than is used in most machine shops to measure the deflection. This, along with the safety factor, is much stronger than what is needed for the building to just support it's own weight.
Enter the imploders. Before starting the process they have carefully studied the plans of the building and verified the actual construction-which can vary from what was originally designed. Much of the internal finishing (and it's associated weight) has been stripped away at this point. The imploders carefully cut the beams and columns in pre-calculated ways to weaken them just to the point where the gutted building is supporting it's own weight and not much more. At this point if you put all the weight of interior walls, furnishings, and people back in the building it would probably collapse, although not in a controlled manner.
Once the building is ready the imploders place charges. These charges are selected to do certain things, such as finish cutting through beams that have already been weakened. The explosives are timed to within 1/1000th or so of a second through the use of electronic firing controls and timed fuses. The explosives do not, repeat do not, actually bring the building down. They cut away the remaining structure in a controlled manner so that gravity can actually bring the building down.
Here's the trick: in most modern steel framed buildings the walls support the floors and the floors keep the walls from tipping over. Take out all the floors and the walls could fall in any direction the wind blows them-say the building next door that is not scheduled for demolition. But you have to have the walls to support the floors. Catch 22. What imploders do is time the explosives in such a manner that the weight of the building after it is cut apart by the explosives causes it to fall into itself. Essentially hundreds of cuts are all made within a few seconds, and then gravity does the rest. If you tried to do it one cut at a time the building would fall in a very unpredictable manner and the stresses realigned themselves with each cut. Picture a plate held up by 3 strings. Cut one string at a time and the plate swings on the other strings and falls unpredictably on it's edge. Cut all three at exactly the same time and the plate falls straight down, flat. Building implosion works the same way but on a much larger scale.
So, to WT7. It may have fallen in a manner that looked like an implosion, but was not. Remember that it is gravity, not explosives, that provides the energy to implode a building. The explosives just make the cuts. If something else, such as flying or falling debris, made similar cuts the result would look similar. If something fell through the middle of the building it would fold up and fall in exactly like an implosion as the floors collapsed and pulled the walls in. Under the circumstances on 9/11 this is not at all unlikely.
No matter how clean the WT7 collapse may have looked the simple mechanics of building implosion debunk the conspiracy theory. A real implosion would have required access to the main structural members of the building, which would have required stripping away the interior finishes. That would have been noticed. Then the beams would have to be cut and hundreds of charges placed and wired. This, too, would have been noticed. If the beams were weakened as usual in implosions the building probably would have collapsed under the weight of the furnishings and people long before 9/11. This would surely have been noticed. If the beams were not weakened it would have taken considerably more explosive than usual, which would have had to be brought into the building.
Controlled Demolition is the company that started doing building implosions some 50 years ago, when the first generation Loizeaux brought down a chimney using explosives. They pride themselves on the precision of their work. I was living in Milwaukee when the bridge failed, and Controlled Demolition was brought in to drop the failed section without damaging the building underneath and around the brige. At the time they talked about how relatively crude the blast would be, and how they were using 600 pounds of explosive instead of 200 because the job had to be done quickly before the section fell by itself. This was for one section of bridge. Think about what would be involved in bringing enough explosive into WT7 to implode it without previously cutting the structure to weaken it. Thousands of pounds of explosives brought in, carefully placed, wired up, and nobody noticed. It just did not happen this way.
I do not expect that the tinfoil hatters will believe anything different after reading this. But now the debunking is written down, along with any comments people care to add, and the next time someone comes along with 9/11 conspiracy theories about WT7 all people have to do is link to this diary. I hope this is useful.