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Basildon Test Report

Series 3 - Collapse Modes

Although the anchor installation was not intended to provide any flexural capacity in the transverse direction to the planks and had only been designed to transmit in plane shear forces to the side walls it was thought it would be interesting to see if the mode of collapse of the structure was influenced by the anchor installation.

To do this some controlled demolition was undertaken and recorded using time lapse photography at five frames a second and video recorders.

The same procedures were used on both Ends A and B and were as follows:-

  1. The end ground floor concrete wall panels which support the ends of the first floor planks, the first floor end wall panels and the ends of the roof planks were cut away to leave a minimal support at the centre and the edges of the end wall (Photo 1).
  2. The remaining central support section was then carefully removed using an excavator bucket.
  3. The remaining side supports were then progressively taken away leaving the end of the first floor unsupported.
  4. The ensuing collapse was filmed and recorded.

Findings

The only way to fully appreciate the mechanisms of collapse which were involved is to study the video recordings and the time lapse photographs. For the purpose of this report a number of the time lapse photographs are referred to which illustrate critical points in the collapse mechanisms.

End A - (anchors in place)

Photograph A4 - Shows the stage were virtually all the load bearing support has been removed from the end of the structure. At this point there is no significant disruption to the structure and the first floor planks have just started to deflect under the load.
Photograph A5 - The last remnants of the supports are removed and the first floor starts to fail slowly under the weight of the panels above.
Photograph A8 - The first floor continues to fail as a unit leaving behind the roof which is unsupported but still intact. The side walls start to buckle out at first floor level under rotational forces induced by the first floor wall panels.
Photograph A10 - The first floor collapse is complete, the side walls are now buckling badly but the unsupported roof remains in place and intact.

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