John Hurle- Associate Structural Engineer, UK
Most of the structural engineers tend to make these common mistakes during the design phase of a project. They are usually too focused on the structural analysis and don’t consider and weigh how important these other aspects could turn out to be. They don’t realize these important considerations that make for a successful project. What structural engineers need to do when they’re designing is to consider at least three more people’s perspectives on their projects. Firstly, to have a customer focus and consider what the client values. Secondly, they need to understand the steel fabricator’s (or manufacturer's) view or else the steel frame could be unduly difficult and expensive to fabricate. Finally, they need to understand the contractor’s perspective or the project will be unnecessarily complex to build and put pressure over the programme.
Understanding the Client
Many structural engineers don’t realize the client’s perspective. They need to have a customer focus to listen and understand what the client values. Not to design a particular solution because it is easier to analyse. Not to over-design to cover for uncertainty. Not even to necessarily design what is most efficient structurally, but to be proactive at seeking out solutions that best meet the client’s overall needs.
For example, one housing association that I worked for wanted flexibility for procurement. They wanted a tender design that could be built from ‘kit of parts’ either using load-bearing masonry, reinforced concrete or off-site construction (also called DfMA, Design for Manufacture and Assembly) such as precast concrete or cross-laminated timber. To achieve this, the layouts had to be checked for every option to ensure they were viable. The benefit for the client here was that they could wait until they had the exact prices from the tender returns to choose which option was best.
Another time I was working for a large developer. They built private apartments and were very keen to create variety and exclusivity. They wanted the apartment layouts to be different on every floor of the high-rise so that each apartment was unique. This required varying the column layouts at every floor and providing transfers where needed. Although the cost and complexity of the structure increased; it was preferred by the client as the value of the apartments increased by a greater amount due to its beautiful finish and exclusiveness.
On a smaller project for an artist’s home, they wanted a mezzanine to create a nice studio space for working on their painting. We were introducing a floor into a double-height space and suggested an unusual floor build-up to provide more headroom. The client instead preferred a different solution as it was simpler visually and made it easier for them to concentrate on their artwork.
In each case, the client had different requirements, which I had to interpret and understand to be able to give them the best possible design within the other project constraints. Another structural engineer may have made the mistake of just doing what was in their best interests, rather than considering the client’s perspective.
Understanding the Fabricator
Lot of structural engineers don’t realize the fabricator’s perspective. They need to have an in-depth knowledge of the fabricator’s processes and equipment. Not to design what is easiest to calculate. Not to over-specify as a shortcut. Not even to necessarily design to use the least amount of materials, but to provide a solution that is considerate of fabrication.
For example, steel is only commonly available in certain grades, thicknesses and section sizes and not all steel sections are commonly stocked, some have to be rolled to order. Therefore, it may be cheaper to use a larger section size or a higher strength grade depending on its availability.
In the UK typically labour is a much higher proportion of the costs than materials such as steel tonnage. Therefore, it is cheaper to use more steel when it economizes on cutting or stiffening, to use bolts instead of welds and fillet welds instead of full penetration butt welds. A decade ago while I lived in India; labour was cheaper than materials, so the opposite approach was appropriate.
Finally, simplicity and repetition are often more important than material efficiency. Balanced against other factors, a good design aims to keep members orthogonal and to minimize the number of types, the number of cuts and the size and number of welds. For example on an office project I led, we standardized the member sizes and grouped the connections into a small number of types which lead to all end plate connections. This reduced the amount of design required and simplified fabrication.
Understanding the Contractor
Unfortunately, many structural engineers also don’t realize the contractor’s perspective. They need to be familiar with how things are built, the likely construction sequence and the importance of the programme. Not to design only for what the software outputs. Not to over-design to hedge against misunderstandings. Not even to necessarily design what is most efficient structurally, but to provide solutions that overall can be reasonably constructed.
For example, I designed for column strengthening at the Energy Centre of a mixed-use development. The strengthening could have been achieved by adding a single (very large) steel column, however I was aware that the access was very constrained and there wasn’t any space for a mobile crane. Therefore, I designed the strengthening as a set of three smaller columns next to each other that could be lifted more easily and then bolted together so that they act as a single column. This required only two men and a simple pulley system to install and was possible without shutting down the Energy Centre.
Another general principle to keep in mind is that the construction sequence should be as simple as possible. Wherever possible avoid hanging structures or cantilevers and limit (or at the very least highlighting) the need for temporary works. For example, I reviewed a retaining wall design for a contractor which showed utilities passing through the wall. I realized early that this would require the utility, ground-works and concrete sub-contractors mobilize and demobilize in a complex multi-step sequence. Therefore, I suggested the design be changed to put the utilities under the wall to simplify the sequence of trades. It's estimated that this simple change saved about five weeks of the construction programme.
In summary I think that many structural engineers could improve their designs if they considered these three stakeholder perspectives. Firstly, to have a customer focus, to proactively consider if the design could be changed to give the client’s more of what they value. Secondly, they need to understand the steel fabricator’s (or manufacturer’s) view or the steel frame will be unduly difficult and expensive to fabricate. Finally, they need to understand the contractor’s perspective or the project will be unnecessarily complex to build and put pressure on the programme.