Blog – Championing Efficiency in Design

By Darren Noller, Senior Structural Engineer, Superstructures

“We now all recognize that we live in a world with limited resources and as a structural engineering business, we are very focused on ways in which we can reduce the use of carbon within our designs.

With sustainability coming to the fore,  the efficiency of a design has never been more important.

Unfortunately, in my three decades of experience, a structural engineer’s reputation among both clients and contractors has often been one of excess. “You could land a helicopter on that!” is something I have heard frequently, when proposing a structural design to support a single-storey extension. Another comment that is all too regular, is that we have taken the “belt and braces” approach to a design.

However, efficiency of design has long been championed by the Institution of Structural Engineers as a significant part of our remit, and here at Superstructures, we see it as a vital element in what we do .

Fundamentally, the approach we take on every project is to consider every aspect, so we are confident that the design we are proposing is safe, efficient, and fit for purpose.

A technical clause from the British Standard Steelwork code BS5950-1:2000 states: “Whilst the ultimate limit state capacities and resistances given in this standard are to be regarded as limiting values, the purpose in design should be to reach these limits in as many parts of the structure as possible, to adopt a layout such that maximum structural efficiency is attained and to rationalize the steel member or element sizes and details in order to obtain the optimum combination of materials and workmanship, consistent with the overall requirements of the structure.”

In simplistic words, what it is saying is that the design should be as efficient as possible and designing in such a way is inherently safe, because the load factors applied mean that the designed members will never reach full capacity.

Of course, other factors come into play, and to ensure the most efficient design may mean that we have to revisit some of them.

For example, one area to reconsider is the deflection of structures, a key area which often significantly impacts the design. Nowadays, within specifications, there is much more scope for clients to have an input on the parameters required, meaning that for certain less critical structures, or elements, the deflection requirements could become less onerous.

Imposed loadings is another area which should perhaps be revisited in the light of actual data. Office loading for instance, is based on an allowance of 250kg/sqm, but in modern offices where filing cabinets are a thing of the past, isn’t such loading criteria somewhat arbitrary?

In addition, our modern methods of analysis mean that it is possible to create full 3D virtual structures of our buildings. These models provide us with much more exact arrangements than previous methods could achieve, enabling us to design each member efficiently without the need to put similar members under one design.

Further improvement in efficiency can be made in detailing and ensuring that enough time is set aside for the design stage of the project. If the design period is squeezed, then it is likely that the design will be, by nature, more conservative and subsequently less efficient.

For example, a heavy steel beam may be specified due to time constraints, but a lighter weight – and more efficient – ‘truss beam’, could have been designed, if there had been earlier discussions with the structural engineer, and a longer design period had been given.

Obviously, efficiency isn’t just about the amount of material used; there are other factors that all members of the supply chain need to consider. For instance, in the previous example, a negative of the truss idea may be how much fabrication is required; however, a positive may be that a smaller crane could be used on the project.

Overall though, as engineers we need to feel confident to take more of a lead if possible, so we can provide options to others in the design team, as well as the client and contractor.

The team of professionals I work alongside at Superstructures are all keen to do everything to implement change for the good of efficiency and the sake of sustainability.

We want to discuss as early as possible in a project, the direction it’s going and work collaboratively to identify areas that could be investigated further. Whether that is in relation to looking at alternative construction materials or ensuring better and more efficient design and detailing. We consider that whatever the project, there are potential efficiencies and sustainable choices that can be made.

Of course we recognise that cost is still a huge factor which can’t be ignored, but armed with our wealth of experience and knowledge, we are able to propose alternative choices, as long as we have the time to give it consideration – I am continually surprised how some of the choices made lead to unexpected savings!

Good design in the 21st century needs to be efficient and we as engineers should be leading the way. It is likely that legislation which puts sustainability at the centre of future construction design will continue to be forthcoming, and it is important that we all recognise this, sooner rather than later.

One thing I know for sure, is that here at Superstructures, we are keen to be early adopters and to help drive the discussion and implementation of more efficient and sustainable design.”