Large Panel System (LPS) building structural refurbishment issues

A reporter from a firm of consulting engineers’ comments on his experiences when refurbishing 1960s Large Panel Structure (LPS) buildings around 2000. In blocks of a particular type, he found that a third of the reinforcement had simply been left out in the slabs on some towers.

The slabs were badly cracked on the soffits, so full scale load tests up to 1.5kN/m² were carried out. It was found that deflections were extremely small, and it was assumed that the slabs were effectively arching.

Carbon fibre reinforcement was however added to the soffit of nearly all the slabs with the recommendation that the strengthening should provide only 30 years extra life and that the buildings should be demolished.

Further concerns with the tower blocks were associated with:

• An external wall of the reinforced concrete (RC) basement structure had been moved off grid some 600mm at the time of building resulting in inadequate load paths so that new steel columns had to be installed

• The concrete partition walls are essential for resisting accidental forces. Measures were taken to fix them at the ceiling to prevent horizontal movement.

• Similarly, basement structures were strengthened to allow loads from these partitions to be transferred to the foundations

• The lounge slabs cannot take accidental loading without some transverse spanning so steel angles have been added to allow for this

• The reporter’s firm rejects the idea that the top floors cannot be saved from an accidental explosion. Once a single slab starts to fall, the energy will be too high to ensure that the next floor down will stop it.

• However, by strapping with angles, ceiling to floor, then in theory the top floor of unreinforced concrete walls will not need to take direct tension, so they can take the accidental bending effects

• The reporter has had instances where lintels in the basement walls have been cut away to save having to shave a door

• Owners believe the there was no way a flat could take 17kN/m² in all directions and have done nothing. In practice, just a little strengthening and some dedicated lateral thinking and analysis will suffice.

There were also many problems with climbing masts during refurbishment. Fixings were coming loose in windy conditions and the foundations were, in the reporter’s view, completely inadequate. The Health and Safety Executive (HSE) inspection staff and the contractors’ H&S team had no training on this, and only the reporter’s engineers appeared to appreciate the dangers of the shortcuts that were being used. Scaffolding and mast climbers appear to have very different standards of inspection and safety. It is recommended that mast climbers should be inspected by Chartered Engineers as well as inspectors.