Should I rationalise my design?

Should I rationalise my design?

Rationalisation of steelwork design is common practice on most projects in the UK. The main drivers for this are constraints on design fees and time and efficiencies in procurement, fabrication and erection of the steelwork.

Reviews of steelwork designs have shown that some material efficiency savings are achievable by not rationalising designs but these studies also conclude that the main cause of over-specified steelwork is conservative engineering assumptions to retain a degree of flexibility or reserve in structural capacity.

Rationalisation of steelwork design is current, common practice on most projects in the UK. The main drivers for this are constraints on design fees and time and efficiencies in procurement and fabrication and erection of the steelwork.

There have been several recent studies looking specifically at the material efficiency of steel structures, see, for example, references [9-12]. These studies suggest that over-specification of sections can lead to an additional 30-40% of steel used within the structure and, therefore, to additional embodied carbon within the structure. While bespoke designs may contribute to reducing the upfront embodied carbon, there are good reasons to rationalise designs:

  • from a safety point of view, less variability in member sizes reduces the possibility of human error during erection,
  • from an execution standpoint, the increase in the speed of construction,
  • from a sustainability or circular economy perspective, rationalised designs enable greater flexibility and adaptability of the building and enhance the reusability of the structural elements.

It is noted that [10] concluded that rationalisation or repetition within the structure could not explain the over-specified mass of the steel frame rather it is the designers decision to limit the utilisation ratio to 0.8 that was the main cause. In addition, there is unused mass in cores, trimmers, ties, etc. and in edge beams which are under-utilised but are necessary for stability. Figure 5 (from [9]) shows the utilisation as a function of beam type from an analysis of 30 buildings.

Other studies have investigated other factors including over-specification of loads and less conservative SLS criteria where SLS governs. While these aspects may help reduce embodied carbon within the structure, they are unrelated to rationalisation of the steelwork design.