MAINTENANCE & REFURBISHMENT The right support in refurbishment
Robin Webster, procurement manager at Site Equipment Ltd, explores the role of propping and needling techniques when planning a refurbishment project
A
s the need to maintain structural safety by avoiding the collapse of existing walls and ceilings is a top priority in refurbishment works, it’s important to consider how that
level of support can be incorporated into your plans. Propping and needling techniques are an ideal means of providing such support and offer a flexible, adaptable option that can be deployed in a wide range of settings. For readers who may be less familiar with these techniques, propping and needling systems are a form of temporary works that are often used to support walls and ceilings while alterations are made to an existing structure. For example, when creating an opening in a load-bearing wall or supporting a ceiling during roof alterations. In most cases, propping and needling systems
are quick and easy to deploy and can be used in all kinds of scenarios.
A good example of a modular propping system with a variety of uses is Slimshore’s formwork soldier units, which come in a range of sizes. These can be used as prop units, raking shores and needle beams, depending on the needs of the project in hand. A range of accessories are available to enable deployment of the soldiers in a variety of settings, including Push Pull Props and Lightweight Adjustable Props. It’s important to make sure the system you’re using offers adequate strength to ensure the loads are transferred to temporary foundations and that deflection is minimised to acceptable levels while the alterations are undertaken. It’s also vital to check that the employed propping solution has adequate measures in place so the lateral stability of the structure is maintained as required.
Propping and needling in practice
Cordwell Leisure has recently rebuilt and meticulously renovated two historic transit sheds on Bristol’s floating harbour in an ambitious project that offers a strong example of propping and needling at work.
The adjoining 19th and 20th Century sheds, known as O & M Sheds, have been let to BoxPark, which will open its first out-of-London new concept, BoxHall, in the 20,000 sq ft space. Based on a similar concept to its successful BoxPark venues, BoxHall Bristol has been described as a food, music and drink hall and will enjoy a prominent location with views across the waterside and beyond. The new design has created a light, open feel with an industrial setting that reflects the building’s heritage, with the opening up of new picture windows and the creation of a feature harbourside terrace to make the most of the surroundings.
Cordwell’s renovation, working with Site Equipment Ltd and its main contractor, JH Group of Bristol, opened up the space to allow greater flow of passage between the two sheds. Instead of utilising two former openings that had since been bricked up, the plans called for new doorways of around 3-4m in width on either side of those openings. This was a relatively complex propping and needling operation. At two internal locations it wasn’t possible to fit propping adjacent to the proposed opening due to the site team having to excavate a trench beneath the new openings to install a ‘picture frame’ structure with a bottom member encased in concrete.
Overcoming obstacles
Changes in the construction programme called for propping to a new roof structure to allow enhanced foundations to be installed along the side walls. It was also used to support the roof while new waterfront-facing windows were added. However, the most ambitious element of the project was the formation of a 14m long opening in the end gable of the site to link the internal space with the external riverside and areas opposite. This side of the building has a prominent position that typically sees a lot of footfall. As well as creating the new opening, Cordwell was keen to tidy this up and restore the end gable to its historic roots with ornate brickwork that reflects its original design. To form the opening, propping was required to support up to 8T per metre of masonry and roof loads being retained above the proposed opening. In addition to supporting these vertical loads, the system was required to sustain significant potential lateral forces. The wall here was built with a thickness of
around 450mm but was reinforced to around 600mm in thickness at the time it was refaced, which meant there was a heavy load to support during this latest reconstruction. Plus, the length of the proposed opening required significant propping together with 13 lateral needles. Among the biggest challenges was the
presence of a large electricity substation close to the end gable, which had an impact on where the opening/propping could be located. As well as prioritising site safety at all times, it was essential to avoid any disruptions to local power supply. This required a complex temporary foundation arrangement and offsets between the supported wall and available temporary
6 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MARCH 2024
foundation locations meant a complex propping solution was needed. Due to the size of the proposed openings, significant structural steel was required to support the masonry above. This further complicated the internal support arrangement to ensure that adequate space was provided to allow the new steelwork to be safely lifted into place. The propping solution allowed the impressive openings to be formed safely, ensuring that the facing brickwork and associated finishes were in keeping with a building of this nature to protect its heritage.
Reclaimed brickwork was used to revitalise the appearance of the end gable and the steel used for the reconstruction will remain exposed to add to and protect the industrial feel of the building. This meant the needling work had to be carried out very carefully as there was no means of hiding any trace of it following removal. The end result of the project is a strong example of how propping and needling can save existing structures and give them a new lease of life.
Read the latest at:
www.bsee.co.uk
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