Just Finished Reading: To Engineer is Human – The Role of Failure in Successful Design by Henry Petroski (FP: 1982)

In another Life, in another Universe I might have been a Civil Engineer. I love the idea of building things like bridges and skyscrapers, dams and tunnels. So when Amazon said I might like this book I took its advice. I was not disappointed.

The narrative starts with a seemingly simple question. After the collapse of an internal skywalk a neighbour asked the author “After all of these years you guys still don’t know how to build a bridge? What’s up with that?” Needless to say that the answer wasn’t something that could be conveyed in a few pithy sentences – hence the need for a whole book. There are several problems with building things – like a bridge for example. In some cases nothing like the particular bridge in question has ever been built before. Maybe the span is larger than ever been attempted or the materials are new or have never been tried in that particular combination. Maybe the expected traffic levels turn out to be half of the actual levels, maybe the manufacturer of particularly sensitive parts bid low to undercut the opposition and used inferior materials to cut costs. Maybe the salt content of the local water wasn’t tested or changed unexpectedly over time due to other building works unknown at the time because they post-dated the bridge being built. Thousands of these questions need to be taken into account and some of them cannot be easily quantified. No two structures are identical nor are two locations or conditions during the build process or in the years, decades or centuries that the structure stands for. Bridges that last far beyond their expected lifespan may be seen as over-engineered overly cautious structures that could be made cheaper, faster and more elegant if less materials or the latest materials are used until, at some point, the bridge collapses and the subsequent investigation shows where a pleasing curve and an elegant span coincides with inadequate bracing and a lack of alternate load paths.

Although much of this excellent brief volume looks at bridges the author evaluates other engineering failures to make his point. I was particularly taken by his detailed discussion of the Comet disasters in the 1950’s where the premier aircraft of its day inexplicably crashed after exploding mid-air before it was discovered that cracks from the then unknown metal fatigue caused explosive decompression long before it was expected to be a problem. Only rigorous testing in giant water tanks revealed the problem before anyone else died. Likewise the discussion of the success of the Crystal Palace created from cast iron prefabricated parts for the Great Exhibition in 1851 was, pardon the pun, riveting. You could feel the authors admiration for the awesome success of what was, up till that point, essentially an amateur engineer. A particular amusing section was on the demise of the slide rule (I just remember them as they’d just gone out of fashion when I started doing Maths seriously) and the problematic use of CAD (Computer Aided Design) software – something I’m very familiar with as I’ve been regularly using it for the last 15 years - as an automated way of making mistakes with confidence. Older engineers can look at the derived figures and sense that they don’t ‘feel’ right whereas younger engineers who grew up with CAD would simply trust it too much. This is exactly what some of my much later technology reading made such a play of – trusting the screen rather than the reality of things.
          
Overall this was a delightful, fascinating and highly informative book. I’m certainly looking at structures in a different way and am paying particular attention to any cracks I see or any unexpected movement I feel! Fortunately the author has produced a number of other books on the subject and I’ll definitely be picking them up. Much more on the subject to come.