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WTC Collapse Simulator

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Download (Updated 24 Apr 2009)

The WTC Collapse Simulator is an interactive application which models the collapse of World Trade Centre 1 & 2 using straightforward physics and energetics principles, and renders the results in real-time using OpenGL.

The underlying calculations can be found in the following spreadsheet:


On September 11th 2001, following structural damage from aircraft impacts, ensuing explosions and subsequent fires, the World Trade Centre Twin Towers both collapsed totally and completely to the ground.

These tragic events have been the subject of much discussion since, as many believe that the collapses were in fact the result of Controlled Demolition, and not an unforseen result of the aircraft impacts, ensuing damage and subsequent fires.

The primary aim of this project is to provide information and tools enabling users to understand fundamental laws of physics which affect the progression of the 'collapse' of the World Trade Centre Twin Towers.

It is not our aim to dictate opinion or conclusions upon anyone, but to highlight simple methods which assist in gaining a clear understanding of the basic underlying phyics of the tragic events which took place.

The Model

The structure of each tower can be visualised with 3 basic elements:

  • The Exterior Walls - A square tube forming the outside of the building, running from the bedrock base to the roof.
  • The Central Core - A rectangular tube in the centre of the exterior wall 'tube', also running from the bedrock base to the roof.
  • The Floors - A thin horizontal slab forming each floor of the towers, attached to the Exterior Walls and Central Core.

The Twin Towers were each 110 storeys high, above ground, plus a further 6 underground storeys.

The Exterior Walls were constructed from 236 vertical steel box columns around the perimeter of the 'tube', with each column being attached to the next by massive horizontal spandrel plates at each floor level forming a dense 'mesh', and with windows filling the space between each column.

The Central Core was constructed from 47 massive vertical steel box columns, with the space inside the core area housing building facilities such as lifts, staircases and tenant storage.

The Floors were constructed as trussed steel meshes bonded with a 4 inch thick layer of lightweight concrete, forming large open-plan tenant space between the Central Core and the Exterior Walls.

The WTC Collapse Simulator Model (The Model) simplifies these basic elements even further.

The Model can be visualised simply as 110 stacked 'Storeys'.

Each Storey comprises the whole of the Exterior Walls, Central Core, Floor and contents for the entire tower structure between one Floor and the next above, including the Floor Slab itself and the physical contents of each floor.

The Model essentially calculates the energy required and expended by the destruction of each subsequent Storey within the progression of any modelled collapse.

The calculations are performed Storey by Storey taking account of the dynamic nature of the collapse, and includes many adjustable Parameters.

Specific attention is focussed on the determination of the effect each Parameter and data change has upon the time that the collapse progresses in.

Each Parameter and all calculations are detailed in full, and the provided source data fully explained.

All data within the model can be changed by the user, enabling open and interactive experimentation.

The Simulator

The Simulator is comprised of two components:

  • The Calculations - A spreadsheet containing all data, calculations and parameters required to calculate a simple Storey by Storey collapse timing, along with detailed calculation of the energetics involved.
  • The Visualiser - An OpenGL based application which allows the user to visualise the collapse in real-time, at any point in time, and from any viewpoint, using the data calculated in The Calculations.

This allows the user to quickly see the effect that changing various parameters has upon the collapse time. 

These Parameters include:

  • Whether the Central Core and Exterior Walls pose any resistance to the collapse.
  • Whether crushing the concrete in The Floors requires any energy.
  • How much mass is ejected from the sides of the Tower.

By understanding the effect of these parameters upon the collapse time and energetics, and experimenting with multiple options, the user should be able to reach an informed personal opinion as to whether the events witnessed on that tragic day point to a gravity driven collapse, or a controlled demolition.

Every effort will be made to explain every factor included, the reasoning behind all simplifications, and why the methods utilized form a valid approach to determining the calculated results.

The full calculation spreadsheet is included below for your reference and experimentation:

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