The redevelopment of St Pancras station involved two elements, the first saw the refurbishment of the existing train shed roof which at the time was the largest single arch span in Europe. The refurb required access and protection scaffolding to be positioned within the roof space so other work to the remainder of the train shed could be completed simultaneously.
Initially there were concerns of whether the roof had the capacity to carry a suspended access and protection scaffold, whether the level of access that would be needed to complete the work could be provided, how the scheme could be provided without interfering with the other refurbishment works and how the scaffolding would be dismantled once completed.
We carried out a quick assessment of what we thought all the self-weight and live loads of the suspended access and protection scaffold would be, this was based on an aluminium bridge panel system, overlain with a corrugated metal decking. The results showed that the train shed roof was in fact quite capable of carrying the load required. The client however wasn’t satisfied even though the results were mathematically correct and expressed concerns about whether the roof would respond differently due to possible long term corrosion. We arranged for further tests to be carried out which involved 10 tonne loads traversed for the full length of the train shed roof, whilst measuring the amount of deflection the roof encountered and compared that to the mathematical models we generated previously. We also weighed elements of the suspended scaffold to confirm that our calculations for the self-weight were equally as accurate as the assessment of the roof structure. Both the models and the practical testing produced the same results and so for the moment, everyone was happy.
We created an exemplar to demonstrate what the scaffolding would look like within the roof space and how tradesmen would get from the lower eaves level to the main centre point of the arch. The sample was erected using chain blocks suspended from the roof and cherry pickers, which reached 33 meters up to the height of the apex, were used to provide access to secure it to the roof. The entire sample section extended 9 meters and was made available for the follow on trades to access to assess whether their requirements were met. Once all parties were happy, the scheme was given the go ahead to fill the whole of the roof.
The method of assembly and installation had to also be carefully thought through as work on the rest of the train shed was ongoing. We decided to assemble all the sections that were to be suspended in the roof at one location which was the town end, winch them into the roof space, connect them into a suspended runway beam connected to an arch, transfer them the whole length of the roof to the country end and stack them up as if in a jigsaw, making sure each section interlocked. Two tower cranes were positioned within the station which had to penetrate the roof and the suspended scaffold. This made the installation of the scaffold quite tricky when it came to transferring the sections down the train shed roof. This meant that some elements of the scaffold needed to be installed straight into the desired position. The completed scaffolding system was supported at 8 locations.
The regeneration of the train shed included blast cleaning, steel work repairs, painting the steel to its original colour and re-glazing. The water power from the blast cleaning was so powerful that it could cut through most materials if not carefully handled, so we had to make sure that the system we designed could withstand any accidental impact. Storage space for equipment was built into the scaffolding deck, it was also water tight to provide protection against inclement weather and protection from the impact against any falling debris or equipment. Materials were transferred onto the protection deck either by the two tower cranes or carried out manually by the tradesmen via the access routes which were provided within the scaffolding system.
Over the period of time the scaffolding was up, reportedly there were no leaks onto the working area below which in itself is an achievement, there were no penetrations through the deck from falling materials and there were no accidents associated with using the system.
The scaffolding remained in place for 18 months as a total package. As work was completed the deck was incrementally removed using chain blocks and subsequently dismantled in situ. Once the deck was completely dismantled it became evident that additional remedial works, which hadn’t been picked up at the early stages of the project, were needed. A new section of suspended deck, 9 meters in length, which traversed up and down the whole of the train shed roof was provided to give access to particular areas.
The project was heralded as being one of the best suspended access systems, firstly because it provided total segregation between the roof and the rest the station for work to be carried out simultaneously and secondly for providing full water tight weather protection which allowed a lot of station finishes to be carried out before the full roof refurbishment was complete.