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Post-tensioning poser for Connell Bros

DEMOLITION contractor Connell Brothers has completed the demolition of the Marks & Spencer store and office block in Manchester city centre, blown up by IRA in June, 1996.

The demolition of the structure was complicated by the threat of an explosive reaction in post-

tensioned concrete beams supporting the office block through columns running down through the store into the underground car-park.

Demolishing the buildings required a very selective process of dismantling, with the roof and upper floors of the office block being broken up into 2-m sections by mini-excavator. Buffers were then fitted to the ends of the post-tensioned beams to absorb potential stress and pockets were cut into the beams to expose the cables so they could be cut.

Connell Brothers dismantled the building around the beams in a reverse sequence to its construction, in order to replicate the stressing programme. It then stabilised the beams by installing 38 universal beams to support them. Umist (University of Manchester Institute of Science & Technology) monitored the de-stressing process.

The contractor lifted the 46 m beams off using a 500-tonne crane and transferred them to its own site for destressing and breaking up. The beam removal accounted for half the contract cost.

Demolition of the rest of the site is due to end next February.