When these uses are combined, the most efficient structure is not that obvious. The result in theory might be a hybrid steel and concrete-framed structure, creating added complexity in the design

past five years to an estimated 9.3 million, and it is predicted to grow by a further 5 per cent in the next five years.

Structural considerations Over the last few years of my career, I have been involved with assessing the structural viability of building high-rise residential apartments over a multitude of different uses, from supermarkets and batching plants to bus garages, railways and industrial warehouse units. Each site is different and has its own unique set of design challenges and constraints. Based on my experience, there are a number of key technical challenges when designing and assessing the viability of an industrial/residential co-located development. These include working out how you blend, integrate or separate the facades between each use, how you maximise the operational efficiency, without compromising other parts of the development, and how you incorporate amenity space and landscaping, while keeping weights to a minimum.

Then there is the issue of providing separation for pedestrian safety without compromising the operational use as well as providing adequate fire protection, ensuring safe evacuation measures are in place for the residents and operators. Noise and potential vibrational effects generated by the industrial use need to be considered in order to keep the impact on residential apartments within acceptable limits.

Increases in traffic flows also need to be considered to provide separation between the residential and industrial uses. Government and local authority targets in terms of reducing greenhouse gas emissions and net-zero carbon targets are further key considerations. The challenge for structural engineers is to seamlessly blend differing structural solutions. Industrial-type buildings are typically steel frame, due to the need for clear internal spaces resulting in long-span structural elements. Lateral stability is usually provided by a combination of cross-braced bays and portal frames. In contrast to industrial buildings, multi-storey residential buildings are typically constructed with a reinforced concrete


frame, with flat slabs and blade columns. The spans between columns are relatively modest and columns can be hidden within party walls. Lateral stability for this type of development is usually provided by reinforced concrete lift/stair core walls. When these uses are combined, the most efficient structure is not that obvious. The result in theory might be a hybrid steel and concrete-framed structure. This creates additional complexity in the design, in particular at the interfaces between materials. The interface between two materials is likely to occur at a transfer structure over the industrial space. Structural elements supporting multi-storey residential apartments over long-span industrial spaces can be significant in terms of size and cost. It is important when assessing the possible solutions to consider all viable forms of construction. Not just material cost, but also buildability, material weight, programme and the distribution of services. Collaboration with the architect is essential to maximise flexibility of the industrial floor space and to reduce structural complexity by aligning cores and reducing transfer elements. Consideration should be given to the use of high-strength and lightweight materials and facades, as the magnitude of loading on structural elements can be significant. Other engineering challenges include structure-borne vibration generated by the industrial operations, which is a potential risk to the residential occupants. There is also the sustainability impact to consider. Co-location developments, due to their complex and heavy structural elements, will result in increased levels of embodied energy and carbon, if not efficiently designed. Structural engineers can influence the design to improve the efficiency of a building. The use of lightweight forms of construction, such as timber or light-gauge steel where viable, will minimise the building weight to reduce the extent of concrete foundations or transfer elements. Optimising structural column grids to achieve thinner slabs, using post-tensioned slabs, and specifying high-strength materials and recycled aggregates, will all result in less concrete being used and a greener, leaner structure. As for the future of colocation, our industry is currently facing huge challenges in tackling a global pandemic, the climate emergency and – in the UK – Brexit. The uncertainty has slowed the construction industry. I’m optimistic that, as a resilient profession, the wheels will keep turning, the future for the mixed-development model is bright, and this will continue to be driven over the next few years by the demand for housing and the growth of e-commerce. As technology and e-commerce continue to grow, the next big challenge for structural engineers could be ‘multi-storey beds over multi-storey sheds.’

Peter Watkins is a director at HDR | Bradbrook Consulting

ADF MAY 2021

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