Historic buildings may look beautiful but they’re not without their challenges, especially when it comes to repurposing the structures to ensure they remain operationally functional, all whilst protecting their heritage. Here, Matt Westhead, Engineering Director – Major Projects explores the challenges that city-centre façade retention projects present and the role BIM plays in their safe and successful delivery.
In the UK, we’re fortunate to have a great number of beautiful and historic buildings on our streets, especially in cities such as London, Edinburgh and Leeds. In fact, it is estimated that there are around 400,000 listed building entries in England. Whilst these buildings are an important representation of our country’s rich history, ensuring they remain functional and fit for modern-day requirements – often centuries after they were first built – can be difficult.
This is where the topic of ‘retro construction’ comes in: an approach that has grown in popularity with the emphasis on reducing carbon emissions, shifting from automatically demolishing and rebuilding to instead considering how existing structures could be repurposed and refurbished. A key part of retro construction, especially when it comes to historic or classic buildings, is façade retention; whereby the perimeter or façade of the building is temporarily supported and protected, while the layout of the core structure is updated to suit more modern demands.
Unsurprisingly, façade retention schemes can be hugely complex, requiring careful consideration of where the existing structure, the temporary steelwork and the new, permanent works all meet. Ensuring that all loads and deflections are accounted for in the engineered design, that there are no clashes between the various project phases and the structural integrity of the façade is monitored and protected throughout construction can present contractors and engineers with major obstacles to overcome. With a large percentage of listed buildings located within densely populated towns and cities, these busy urban locations provide added challenges when considering a façade retention project.
On these projects, BIM and digital engineering can have a big role to play. Attempting to design a façade retention scheme using 2D methods can be an incredibly time-consuming process, given the number of sections to be created independently and various propping arrangements to be considered, in order to arrive at the optimum design. The scheme would also be more susceptible to clashes between the temporary steelwork and the existing structure and/or permanent works. However, by using a BIM workflow, structural engineers can automate repetitive tasks, easily check for clashes and fully incorporate the temporary works design within a project’s BIM model, ensuring extensive coordination with the existing façade. Engineers can also determine the most efficient system design in terms of the number and weight of steel props needed to support the façade, resulting in cost, material and time savings on the overall project.
With the correct 3D scanning or surveying hardware equipment, digital engineering teams can also take a detailed scan of the whole existing building and façade and import this directly into their chosen BIM software. This then enables engineers to design the temporary propping works around the existing structure, ensuring high levels of accuracy and detail.
This idea of bringing the real site into the context of the digital 3D environment is particularly valuable on city centre projects, where densely populated and busy urban locations can provide an added challenge. Here, the 3D environment can allow teams to model and consider not only the individual building in question but also the context of the wider site, including adjacent structures, public footpaths, roads, transport links and live underground infrastructure assets. This allows for improved visibility of the whole location and context of the project, helping to more efficiently identify any potential challenges, clashes or areas of concern, prior to getting on to site.
Another aspect of access to consider on urban projects is from a logistical point of view; how you will physically get the required steelwork onto site. For example, you may be limited in terms of the size of transport vehicles available, depending on the roads surrounding the construction site. After all, city streets are not always suitable for large cranes and articulated vehicles. In the event that the vehicle size is restricted, you have to get smart about the framework design. Understanding how you can engineer the most efficient design can be invaluable. Whether that’s in terms of reducing the amount of steel needed, meaning fewer deliveries, or using shorter pieces of steelwork, which can then be connected together on site to make spanning trusses or braced frames.
Here, crane lifting tools available within BIM software packages can be invaluable, enabling you to generate the centre of gravity of components - critical when it comes to planning crane lifts. Schemes can also be designed with the crane’s known capacity in mind, taking a proactive approach to the site logistics.
Even just the enhanced visibility that is enabled by BIM can assist with on-site construction, access requirements and planning logistics. Immersive reality technology can take this further still, such as EVE – a digital design tool that fully integrates with Revit, Navisworks and Civils3D software. Rendering a fully explorable visualisation of your project, EVE allows users to explore the site and proposed temporary works design scheme in a real-world environment. This can be especially valuable when it comes to considering access, on-site installation or tight tolerances. For example, while something may look achievable in the technical 2D drawings or model, it could only be when you dive into the 3D environment that you realise the installation of a proposed steelwork prop or delivery of a proposed connection type would be difficult, or even impossible. Essentially offering a digital rehearsal of the works before you reach the site, such visibility and interactivity can be especially key when it comes to complex façade retention schemes in our towns and cities.
While some people may assume that the temporary works aspect of a project is completed once the building façade is successfully propped, this is not necessarily the case. With the retention framework representing such a significant part of the project’s enabling works, it’s vital to ensure that the propping system continues to protect and preserve the structural integrity of the building and façade - both from a health and safety and a heritage perspective. With such projects often involving the partial demolition or remodelling of the remaining structure behind the retained façade and the commencement of heavy construction works, intense vibrations are largely unavoidable. However, if not correctly managed, the effect of these vibrations on the façade’s structural integrity could be disastrous.
To proactively avoid such a situation, structural monitoring solutions can be incredibly useful and valuable in this environment. This technology will continually monitor a structure’s behaviour and performance, and identify any changes in load, rotation, displacement, strain, fatigue, vibration and deflection. A project’s engineering team would be provided with information about any structural changes in real-time, giving them the ability to react to any potential issues quickly, safely and efficiently.