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Out of danger

Demolition - The ghost of Madrid's burnt out Torre Windsor will not haunt the city for much longer. Bernadette Redfern watched the demolition.

As each mangled section of Madrid's Torre Windsor is lowered a team of workers rushes in to help the crane driver position it on the ground.

So far demolition has taken the building over half way down and by the end of August the charred black outline of the fire ravaged building, standing oppressively on Madrid's clear blue skyline, will be gone.

Almost immediately after the February blaze, which raged for 19 hours leading to partial structural collapse, Madrid's city council appointed contractor Ortiz Construccionesy Projectos to deconstruct the tower.

Fears were that the weakened structure could collapse completely, posing a threat to the metro that crosses beneath the site, and to the buildings crowded around the vicinity.

'Usually we would undertake controlled demolition with explosives but in such a congested site this was just not possible, and it would not be safe to go into the building to plant the charges as it is too unstable, ' says Madrid's department for building control head Emilio Garcia de Burgos.

When the fire broke out on the 21st floor, steel perimeter columns on the upper levels of the 32 storey building buckled and collapsed in the heat (NCE 17 February). These columns, which supported the facade, took with them sections of the concrete floor slab and several supporting concrete columns. Only the presence of a solid concrete floor at level 17 prevented the collapse from moving progressively down the structure (NCE 5 May).

'We knew the deconstruction was going to be challenging as there were elements that were completely unpredictable, ' says Ortiz project manager Jose Luis Cano.

'All of the facade steel was just hanging from the building and we had no idea how the structure would react as we tore it away, ' he explains.

The steel was, however, removed early on without any problems and the team is now moving through the remainder of the structure.

The shriek is deafening as two 70t capacity cranes work in tandem to heave out massive slabs of concrete and steel. The largest section to be removed so far weighs 63t, and it takes several minutes for a piece to be lifted clear.

'First we drill holes into the section of floor we are going to lift out and then lock in the steel cables for lifting, ' says Cano. 'A remote controlled pecker is used to break out the concrete and the cables begin to take some of the tension. Flame cutting is then used to sever the steel reinforcement, carried out by men hanging in a basket over the slab.' Operations take place under the watchful eye of the police who are still investigating the fire and are carefully studying debris removed from inside.

Arson has not been ruled out.

Progress is impressive. 'We are clearing a floor in a week and a half, ' says Cano, and should complete in almost half the time originally predicted.

'The ontractor's roductivity rate is faster than expected but due to the nature of the work it was very difficult to predict how long it was going to take, ' says Garcia de Burgos, the man ultimately in charge of the site.

The biggest risk is that work could trigger a secondary partial collapse.

The building was in the middle of a three year refurbishment which included the application of fire protection to the steel (NCE 2 June) and had got only as far as the eighth floor. Members on the ninth floor are now buckling.

'As we remove members above this floor the loading changes and alleviates the compressive forces in the ninth floor columns, which could lead to further fractures, ' he says.

So 5.3m long steel sections are being welded to the eighth and 10th floor members, enabling load paths to bypass the ninth floor.

'We could not weld on to the damaged columns or connections as this could have introduced torsion into the rigid joints, which could also induce failure, ' he says.

'We would have liked to just go in with temporary supports but we could not enter the building on this floor, ' he adds.

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