As weather continues to degrade the spalling, fire-damaged tower block, more props are to be installed this summer but it is now time to take the emotionally tricky decision to demolish, engineers say.
The Ministry of Housing has released a report that it commissioned from consulting engineer Atkins. This concludes: “There is unanimous agreement and unambiguous advice from all the technical experts and engineers involved in the Grenfell project that the Tower should not be propped for the medium to long-term but should be deconstructed at the earliest possible opportunity, with deconstruction commencing no later than May 2022. This advice is based on protecting the safety of those working in and living around the tower.”
The Ministry of Housing then got Atkins’ work checked by John Roberts, senior director of structural engineering at rival Jacobs. He endorsed the recommendation that Grenfell Tower should be taken down following the completion of the safety works.
Temporary propping has been installed throughout the building in two stages. Stage 1 propping was installed immediately following the fire to the most obviously damaged areas observed at that time to enable emergency response. A proprietary Stage 2 propping system was then installed to provide additional reassurance and to facilitate the investigative processes, inspection and monitoring access and ‘debris’ removal.
The propping designer, Cantillon, designed the propping to distribute loading across several floors, using the residual strength of the undamaged floors. Because of the amount of plant in the basement and obstructions at the lower levels it was not practicable to extend this propping into the basement.
Cantillon has advised that the Stage 2 propping is nearing the end of its design life and it has therefore become necessary to introduce a supplementary and more robust propping system. This supplementary propping system has been designed to minimise risk of collapse and facilitate the floor by floor deconstruction of the building at the appropriate time following a decision. Installation will start in summer 2021.
If the government delays a decision the basement will need propping as well.
The Atkins report states: “The key point from an engineering perspective is that, if no decision has been taken to move seamlessly to deconstruction at the earliest possible opportunity, currently programmed for May 2022 upon completion of the installation of Stage 3 propping from the 4th floor to roof, then propping to the basement also needs to be completed to a similar timescale, however a slightly later completion date to these works of a few months will not make a material difference. The key issue being that, if required, the propping to the basement will need to be in place by the end of August 2022, namely before the onset of winter. Clearly, this would need to be confirmed with the successful Principal Contractor on their appointment (scheduled for May 2021) as to the latest date they would need to be instructed to commence / complete basement works.
“Atkins assessment is that a decision in early autumn 2021 to move seamlessly to deconstruction would accommodate this, however, should the new Principal Contractor deem that an operational decision was needed sooner to meet these revised timescales that would need to be given further consideration.
Grenfell Tower in west London caught fire on 14th June 2017, resulting in 72 deaths. The fir spread much more quickly that had been expected because the building had recently been refurbished with flammable cladding and a inadequate fire breaks. The cladding system acted as an accelerant for flames and a conduit for smoke. It soon emerged that this refurbishment – and many others around the country – had used products that were not fit for purpose and did not meet building regulations.