Keeping the best bits

What goes up, doesn’t necessarily want to come down when it comes to work carried out by the demolition industry, as Andrew Jones, chief engineer for RMD Kwikform knows all to well. For it is his team’s job to make sure it designs systems that can be used to ensure the best bits of a building or structure are preserved for the future.

Thanks to the increasingly popular redevelopment of buildings on inner city brownfield sites is façade retention is now an important issue for both developers and demolition contractors.

With heavy penalties and the UK’s heritage at stake, it is the role of Andrew and his engineering team to support the work of RMD Kwikform’s specialist Repair Maintenance and Improvement (RMI) division, run by Chris Holland. Having recently expanded to cope with the increased demand for larger and more complex façade retention solutions, the RMI team has already been involved with some of the UK’s largest and most ambitious schemes.

Andrew: “To most people in the industry, façade retention has been seen as a basic exercise using tube and fitting or timber shores. There is nothing wrong with this approach, but it does have its limitations and can prove to be inflexible to the needs of the site and the overall programme development. By replacing this approach with a more professional engineered solution, we are able to design systems that can support larger façades using a smaller amount of equipment.

“The challenge for any façade retention project is to minimise disruption, whilst providing an inherently safe and strong support system, that is both easy to build and cost effective. The best way to achieve this is to take as much advantage of available equipment and systems as possible, so as not to rely on specially fabricated parts that can push up costs.

“For example, when designing façade retention systems at RMD Kwikform, we are able to utilise a combination of existing equipment in the form of our heavy-duty Megashor propping and primary Superslim Soldier beam products. With a range of eight Megashor strut sizes from 15mm to 5400mm, depending upon the required strength of the façade, equipment can be taken off the shelf in order to construct a system. The benefits of using Megashor relate to its unique 1,000kN axial load capacity and high axial stiffness which allows a system to cope with even the harshest of conditions.

Using a tried and tested product like Megashor also has its advantages when it comes to more complex site issues, like access and support, as the product has been developed to include a complete range of accessories from screw jacks through to specialist hydraulic units. Fixing points have also been built into the design of the Megashor struts to integrate with our Superslim Soldier primary beam range, that is used to brace the overall system.

The beauty of using Superslim Soldiers in this way, is that the weight of the overall system can be reduced, as the beams have been designed to offer an unrivalled strength to weight ratio. It is however the exploitation of the flexibility offered by this approach that allows us to engineer systems with high leg loads and large spanning members. This in turn enables us to develop an open framed solution and design that can cope with the specific needs of a project. This gives the contractor more space to construct the new structure within the confines of the previous building, giving large access areas whilst creating a safer environment.

From a practical perspective it is essential that façade retention designers have an understanding of the overall demolition programme plan. This is why we work closely with the demolition contractor throughout the tender and active phases of the project. For example, when working on the G1 project in Glasgow, a city centre development that required the retention of a façade spanning some *** sq metres on three different sides of the building, we worked with the primary contractor at pre-tender stage.  We were then able to develop a solution that was incorporated into the main tender package for the demolition contractors.

By sharing ideas and experience at this early stage, we were able to have a much clearer understanding of the challenges we would face. In the case of G1, being a prime city centre location, a key consideration for the design was accessibility, as pavements and parking spaces had to remain open throughout the project. Leg positioning was also challenging, as a high concentration of services in the road prevented the construction of numerous sets of pilled foundations. We therefore designed a system with the minimum number of legs possible, taking advantage of the higher leg loads achievable using Megashor.  From the demolition contractor’s perspective, this also meant that no extra work had to be done to design a system once the contract had been won, so work was able to commence on site for this particular project almost immediately.

As with most developments of this nature, you never fully know what some of the issues will be until you start the erection process and work on site. This is why opting to use a system based on proprietary equipment can deliver significant benefits, as it gives you the versatility to change things easily. This enables quick and simple alterations to be made to the system and also ensures that any parts damaged in the erection process can be replaced quickly, reducing the impact on programme time.

So, with a proprietary system, if problems are discovered once work has commenced onsite, you are able to go back to the initial drawings and remodel the system. In these circumstances, at RMD Kwikform we go back to our three dimensional frame analysis package to ensure any changes to the design don’t have a negative impact on the system. This programme works out the actual member stresses and the structural deflection that the façade retention design has to deal with.  As with the initial design, the thickness of the façade and wind loads should also be recalculated and taken into account, with the worst possible wind patterns considered and designs drafted to meet the British standard wind code BS6399.

In contrast, if no alternations are necessary you can take advantage of offsite preassembly and the significant benefits this offers, particularly where space is limited. For example, preassembled units can be loaded onto wagons at a yard and simply driven to site, where they can be lifted into place using a crane. This is also a positive when using proprietary equipment, like  Megashor and Superslim Soldiers for crane assembled systems, as these products are lighter than their structural steel equivalents, allowing customers to benefit from the reduced cost of hiring a smaller crane. 

As well as using this approach for the Glasgow G1 project, we were also able to use the strength of the building in the overall design, with the box shape of the structure allowing the corners of the building to look after themselves. In the case of G1 we were also dealing with a partially demolished building. In these circumstances it is important to understand the behaviour of a structure, as a partially demolished building will behave differently to one that is intact. So depending at which stage of the project the façade retention is required, identifying where extra support may be needed as the project progresses is equally important.

Finally, in addition to performing its key role of securing the façade a modern retention system also has an aesthetic role to play, particularly in relation to larger city centre projects. Depending upon the site itself, individual schemes can also be turned into revenue generators, through the use of large scale banner advertising.

For these particular projects, using equipment like Megashor and Superslim Soldiers, means that no alterations to the façade are necessary and the attachment of banners is easy, with the holes in the system allowing large banners to be attached around the structure. In some cases this can partially pay for the cost of the façade retention system. This is one reason why demand for our solutions has increased significantly, as customers know that no remedial work has to be carried out to enable them to benefit from this additional revenue stream.

In conclusion, with the rapid redevelopment of inner city brownfield sites and a greater focus on breathing new life into larger buildings and structures, making the right choice when it comes to façade retention can have a major impact on programme times and development costs. Keeping the best bits for the future.