© 2009 R W Clarke

New software aids blowdown

 

Controlled Group, the Yorkshire based Demolition Company, have just successfully trialed, for the first time in the UK, a new collapse simulation software package from the US company ASI. And the results were impressive.

 

On Sunday 22 June former Newcastle and England manager, Sir Bobby Robson, pressed the button to detonate the explosive charges that brought down the old Newcastle Brown brewery building.

 

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Designed Collapse Mechanism

 

 

 The similarities between the predicted collapse and the actual collapse were impressive' says Controlled Structural Engineer, Rob Clarke. 'We removed the end elevation masonry panels and pre-weakened the side elevation columns to encourage hinge formation. The suspended ground floor slab connection at the top of the basement retaining wall was removed in order to protect the wall from being pulled in as the slab drops. An earth bund was formed against the inside face of the wall to balance the earth pressures. We estimated the hidden design parameters, such as reinforcement amounts and details, joint stiffness, etc. This information was added to the 3D model to give a fairly close representation of the actual pre-weakened structure.

 

 

 

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Extreme Loading 3D collapse simulation

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The dust cloud quickly obscures the collapse

 

 

 

It took two days to build the model and then another two days to run the program. Extreme Loading by ASI calculated the freefall trajectory of each structural element and the interface forces between adjacent elements, both connected and separated, something which Finite Element Analysis is just not capable of'.

 

 

 

The 1960s reinforced concrete brewery structure was 60m square by 40m high. The designed collapse mechanism focused around the columns in the centre of the building being destroyed first and then the floor slabs, with their vertical support gone, sagging like a heavy net and pulling the sides of the building into the centre. However, this was complicated by the long-span barrel vault roof which provided the top floor with a virtually column free space. The four vaults were supported on 2m deep post-tensioned beams each spanning 40m.

 

Selected internal columns were detonated in a delayed sequence that forced one end of the roof to hinge at the external face and drop into the centre of the building footprint. This collapse mechanism was essential to avoid structural damage to the flats and offices that were built only 10m away from the Brewery.  

'It was reassuring to see that the results of the simulation were as we expected, but of more value', says Rob, 'was the fact that the simulation did not produce any unexpected issues, such as rogue columns falling away from the building and potentially damaging the neighbours. The barrel vault roof would have been very difficult to deal with using traditional demolition methods. A lot of temporary props and ties would be needed to enable conventional demolition.’

 

 

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Much of the debris pile is in the 6m deep basement

 

 

 Controlled Group had cameras strategically placed to record the actual events. The demolition and simulation will also be the subject of a documentary being filmed for the Discovery channel.

 

It is always a tense moment just before the button is pressed, and this was no different.

 

After the dust had cleared the debris spread was seen to be just as predicted by Controlled and ASI. Studying the videos afterwards showed that the collapse had worked just as planned although there were some subtle differences. The speed of the drop was a little faster than expected. This was probably due to the fact that there were no internal walls left in the building to slow the collapse. In hindsight possibly Controlled could have charged fewer columns but that can increase the risk of a stand-up and the important thing is to have the debris pile as low as practical for processing the material afterwards.

 

'We will definitely be using the Extreme Loading software again' says Rob. 'It can provide a very useful check against collapse mechanism designs, although as with all design software, the results can only be as accurate as the data input. We now have more confidence in the Extreme Loading output and that confidence will grow each time it is used. It is great to be able to show a client and interested parties what you expect to happen on the day of the blowdown. The next stage for us will be to use the software to refine the designed collapse mechanism by tweaking the model and trying out different delays and collapse scenarios.’

 

Learn more about Extreme Loading ® for Structures technology used on the project at www.appliedscienceint.com.

 

 

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