Large Panel System (LPS) was a popular method of construction in the UK for high rise flats until the dangers were revealed by a gas explosion that killed four people in the 1968 collapse of Ronan Point in east London.
LPS buildings do not have a structural frame and are constructed using interconnected concrete panels supporting the concrete floors. As a consequence, LPS buildings are considered at risk of disproportionate collapse in the event of an explosion within part of the building, if they were not originally designed to withstand the forces from such an event.
Birmingham City Council commissioned structural engineer Curtins to come up with a solution to make its old pre-cast LPS towers safer.
Curtins was invited to design a retrospective solution to prevent disproportionate collapse for the council’s LPS buildings. The design it came up with involves the installation of a steel brace on the outside of the tower block that ties the external loadbearing concrete walls, and the upper internal loadbearing walls, to the floors. This brace enables those components of the building to act together to withstand the forces in the event of explosion, with the building remaining structurally stable. The steelwork is insulated with a non-combustible external wall insulation and clad with a more attractive render.
Curtins says that this solution minimises the disruption and intrusion to the building’s occupants while the installation work is being undertaken, as it only requires the decant of certain floors rather than the whole block. The end result is a significantly safer, warmer, visually more-attractive place to live, with improved thermal performance and an associated reduction in energy consumption, the engineers say.
The new solution is to be trialled by Birmingham City Council this year on an LPS high-rise block in the three city areas. Birmingham City Council is the largest social landlord in the UK and the Curtins solution is the first design innovation for LPS tower blocks that has been adopted.
John Healey, an associate at Curtins with over 35 years’ experience in this type of work, said: “We’re pleased to be introducing this new solution for LPS buildings. The lack of a structural frame in LPS towers means that these buildings are potentially at risk of disproportionate collapse. Piped gas heating has therefore been banned to minimise the possibility of a gas explosion. However, the buildings are still susceptible to non-piped gas explosions and their concrete façade means they’re thermally inefficient.
“Primarily, our solution will ensure that in the event of an explosion, tenants will be able to vacate the building safely. The introduction of our innovative galvanised steel frame and cross stitching on the upper levels will prevent deflection of the loadbearing walls, which can cause them to collapse. The second major benefit is that the non-combustible external wall insulation and cladding will make the buildings much warmer, which is great news for the tenants and the environment.
“Many local authorities in the UK have one or more LPS buildings, so our future strategy will be to introduce the solution across the UK to improve safety nationwide.”