The 9/11 Forum

Intelligent and evidence-based discussion of 9/11 issues

Skip to content



Our vision is to provide a home to sincere 9/11 researchers free from biased moderation and abusive tirades from other members.

You are currently viewing our boards as a guest, which only gives you access to view the discussions. New registration has been temporarily enabled; take advantage of it!

WTC Twin Towers Collapse Dynamics

Topics of a general nature, not specific to a timeline.

WTC Twin Towers Collapse Dynamics

Postby Major_Tom » Sat Apr 30, 2011 4:32 pm

The complete collapse mechanics of each tower can be written as a combination of two types of motion.

1) Uneven ROOSD

2) Dropping of 4 perimeter walls

ROOSD is described in the OOS Propagation Model

A simple way to understand the motion of the outside walls: 2 skyscrapers with 4 walls each, giving us 8 separate walls. Each wall is identical to any other, so a general perimeter model of a single wall is introduced and then compared to each of the 8 walls separately.

A general single wall model demonstrating the basic movements observed is linked below:

Single wall model


Some important principles of how walls fall:

1) The MER belts (fls 74-78, fls 40-44) play a crucial role in how a wall falls. They cause walls to fall in discrete stages. Walls can peel as single units between MER levels or they can fracture and fall very close to the base of the building, depending on the condition of the MER belt.

2) Uneven ROOSD can cause a wall to twist as it is shed from the building.

3) DIfferent walls drop in different ways depending on these basic observable principles

The 2 most extreme cases are WTC1 west face (long) and WTC2 south face (short). The WTC1 west face fell out as a curving 50 floor sheet, falling long and out from the base of the building. The WTC2 south wall fell as fragmented pieces and angled sheets, an 80 floor perimeter fitting into a very small space up to the base of the building across the street.

WTC 1: Recorded Motion of the Perimeter Walls

West Wall


South Wall


North Wall

Posts: 3278
Joined: Wed Jul 09, 2008 5:04 pm


Re: WTC Twin Tower Collapse Dynamics

Postby Major_Tom » Sat Apr 30, 2011 4:44 pm

WTC 2: Recorded Motion of the Perimeter Walls

East Wall


West Wall


South Wall

Posts: 3278
Joined: Wed Jul 09, 2008 5:04 pm

Re: WTC Twin Towers Collapse Dynamics

Postby Major_Tom » Thu May 12, 2011 1:57 pm

Space reserved for global wall model
Posts: 3278
Joined: Wed Jul 09, 2008 5:04 pm

Re: WTC Twin Towers Collapse Dynamics

Postby Major_Tom » Thu May 12, 2011 2:12 pm

Open for comments. Thanks for the patience.

I want this to be different than the other presentations in that I want the product in the OPs to be easy to understand and access for everybody. In other threads sometimes we want to focus on technical issues and we don't really care if everyone can understand us.

In this case, the most important thing is that this information is presented in the simplest way possible without sacrificing any detail.

This is different from a "scientific study" in that I want anyone to be able to follow the real collapse dynamics that wants to learn about it.

An important lesson about 9-11-01 is that technical people on the whole are much less intelligent than they think they are (OWE is one noted exception). :?

Writing a paper in a language that is only accessible to technical minds is relatively useless unless those technical minds get off their technical asses and inform others in the population about it in a clear way.

Guys, this isn't going to happen. Technical minds lying to themselves, each other and others lies at the root of the problem.

Information technical in nature must be presented in a way that quite ordinary people can understand and find informative. This way they do not need to rely on those in more technical fields, many of whom do not perform their proper responsibilities in such a debate as citizens or human beings.


The point...I want this to be something you, an ordinary guy, can use to dispel common myths you hear from so-called "experts" filled with hot air.

I want something you can show your cousin, or your grandma (no kidding) . Something an average person can use to understand general motion of the towers.
Posts: 3278
Joined: Wed Jul 09, 2008 5:04 pm

Re: WTC Twin Towers Collapse Dynamics

Postby SanderO » Thu May 12, 2011 6:33 pm


I think your last post raises some excellent points. Toward the end of understanding complex technical issues and explanations if one is trying to reach the non technically qualified... and this includes virtually all the people interested in what happened on 9/11 with a few exceptions... it is important to have several presentations about basic structural, physics and engineering principles.

Take for example the public's (virtually all in the truth movement) understanding of how the floors are "connected to" the columns... ie how loads on them... including the floor's dead load is transferred to the columns and how the column loads are transferred to the column below them and down to the foundation and bedrock. The floors then are literally suspended between the columns which "carry" the floor loads... and so the ROOSD explanation is about FLOOR failure and not COLUMN failure and so the strength of the columns matters not. The columns could be 20 times stronger and a ROOSD event can take place. WAY WAY WAY WAY too much is made of the safety factor of the steel columns (I'm working on that anyway and the FOS I think will be about 1.5 anyway I project). FOS has NOTHING to do with ROOSD.

Another misconception is what is collapse of the floors? This is understood to be a "pancake" drop and this is the least likely of the failure modes and ROOSD characteristics. So the driving "force" of ROOSD and floor collapse/destruction needs to be made very clear.

The floors were composite and this also needs to be explained for the lay person. The floor's components work together but can fail independently... such as the slab fractures and breaks, but leaves the truss in place, perhaps bent??? Or a truss seat could fail and the truss drops and the concrete fractures above it. Or the welds of the truss bars give way, the bottom chord detaches and the truss is no longer capable of carrying any load... the slab will fracture. Ultimately the floors break apart, drop and begin to aggregate into the threshold mass and then ROOSD kicks off.. then the "assault" of the descending threshold mass on an intact composite floor becomes the ROOSD driver. Overloading a floor system to failure is a basic concept of engineering.

What is the difference between a static load and a dynamic load. The ROOSD driver is a dynamic load. It is not simply adding mass in a static manner to an intact floor... which likely could support 3 or 4 times its design load (static). How much load does a floor mass (or any mass for that matter)... have compared to its weight (static load)?

How much resistance can a composite floor offer to the ROOSD dynamic load? And does the ROOSD dynamic load increase as the front descends from the top to the bottom... or does it remain the same... the same threshold quantity? What magnitude of dynamic load could a typical tenant floor resist or arrest.

Understanding of what happens to the broken up floor mass in those 10-15 seconds is also important. Where did it go? What was its volume? Did ROOSD push the facade away... in addition to destroying the floors it descended on? How did it do that? How long can a typical WTC twin tower tenant floor resist a ROOSD driver? How much time does it take to go from intact to crushed, fractured and destroyed? What IS destroyed by ROOSD? What does floor destruction or collapse mean?

How does bracing strengthen a column or a wall? What happens to tall columns or walls as the slenderness ratio increases... the result of losing their bracing? What does self buckling look like?

These are some of the questions lay persons will ask or need to understand about ROOSD. The complex technical OWE stuff is over the heads of most people and they don't need to know it. They need to know that the OWEs of the world "can do the math" and support the theory (at some point in time).

People can believe their eyes if they understand what they are seeing. That's the goal here.
Posts: 1976
Joined: Thu Apr 15, 2010 10:29 am
Location: ny

Return to WTC1 and WTC2 - General

Who is online

Users browsing this forum: No registered users and 0 guests