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Art and Approximation: A Review

Art and Approximation: A Review

“It’s better to be roughly right than precisely wrong”

Attributed to John Maynard Keynes (an economist), few quotes so accurately reflect my experience in design. Throughout my career I’ve become increasingly technical- I even sit in a dedicated analysis team! I have a dirty little secret, however; if I can get away with doing something simply by hand, I always will.

Getting a ‘feel’ for how a structure should be behave really is a key skill, and one I, at least, definitely suffered from never being explicitly taught.

The fact is, in these modern times, especially as an under-/graduate, it’s easy to find yourself elbow deep in code clauses and finite element analysis output without a sound understanding of how/if what you’re designing actually works. And while the digitalisation of design is an exciting prospect; computers are fallible, and programmers even more so– garbage in, garbage out.

Hugh Morrison’s “Structural Engineering: Art and Approximation” focuses on what he terms “a visual approach to design”. The book aims to help engineers (and architects) learn how to get a ‘feel’ (lit. approximation) for how a structure should be behaving and the magnitude of forces, etc. that it should be supporting. This really is a key skill, and one I, at least, definitely suffered from never being explicitly taught.

Starting with an appraisal of what it means to structurally engineer something (firmitatis, utilitatis, venustatis), Morrison starts to build his foundations with simply supported beams; increasing complexity of form all the way up to fabric structures and dynamics. You might roll your eyes at having to review simply supported beams; but I wonder how many of you really know that maximum deflection of a cantilever is 10 times that of a simply supported beam, and how you can use that information to validate designs quickly…

What the book does best is walk the line between mathematics/physics and codes. There are no long derivations of formulae; you won’t be told how to Hardy Cross fixed moments, but you will be reminded why. And there are also very few mentions of the codes; “because ASCE says” is not the reason something works structurally- of course, you do have to get it to work the your codes, but that’s not how you design it.

I would recommend it to all graduates entering design, it’s a way to get some judgement that normally takes a few years of experience.

Instead this book focuses on how to engineer structures through art and approximation. You won’t come away with a detailed knowledge of everything, but it’ll at least set you on the track to being able to see if a design is sensible, if your validation method is appropriate and the questions you should be asking your specialists. And in a field as diverse as engineering (the nine pages on fabric structures now represents my sum-total knowledge of them,) that’s a useful thing to have.

What I also liked about the book, was its gateway nature. There’s quite a few references to other, more detailed, texts on each of the major subjects- so if you find yourself being drawn into the world of tension rings, you will be pointed in the right direction. (n.b. I’d like to take this moment to remind ICE members that you have access to a huge library of engineering books…)

I think this book has a few audiences. I would recommend it to all graduates entering design, it’s a way to get some judgement that normally takes a few years of experience. I’d say it’s a helpful tombe for those entering conceptual design, also, where spending six months doing a detailed study of bridge vibration won’t make anyone happy. And I’d also recommended it for the chartered engineer who has been managing too long and the technicals who could do with a bit of broadening.

Structural Engineering: Art and Approximation

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  1. It’s a good point, in fact the IStructE professional exam tends to highlight this with perhaps less attention on detailed design of various elements (beams and columns) but greater emphasis on how your structure works with regard to concept and particularly stabilty via bracing, shear walls, diaphragm action etc. After all,most candidates should by this time be able to design a beam but the overall picture might not be so obvious to some.

  2. Great Article. My years doing technical support have shown me that Young, & Seasoned Engineers, do have a broad range of abilities in understanding structural form. Often would I get the question “why do I have moments here or where does this force com from”. 1st port of call is let’s look at the deflected shape and compare it to the applied loading.

    A great book is “Understanding Structural Analysis” by David M. Brohn


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