Go figure

In honour of the V&A’s engineering season, Maria’s column is written this month by structural engineer Steve Webb

I clear my desk and push my computer right to the back. I sweep my hand over the white tabletop a few times to clear the snots of eraser and dust. Quite empty now, it suggests I’m in control and have comprehension.

 I print the drawings and arrange them to my left. I place a rubber, my calculator – bulky and filthy – and a scale ruler on the right. Then I find a calculation pad. I try to find a fullish one of heavy stock, thick and flexible. I get a pencil. The pencil I like is a propelling Pentel P209s with a 0.9mm soft B leads. They’re slightly top heavy so they lean back a little into the cleft of my thumb and forefinger. A 0.9 B lead, not brittle or feint, allows for decisiveness and bold action: big clear dark figures. 

 Engineers still calculate most things by hand. This seems very strange to me as so many things today are automated. The hand calculation invites numerical error and it’s laborious. But it allows nuance and approximation, and its slow pace and meditative nature give other parts of the brain time to unconsciously weigh what I’m doing. I never feel like I am working if I’m not calculating. The muck has to be shovelled. I’ve got to turn pages of information into proven conclusions.

 I put the pad in the middle of the desk and lower myself into my chair before it. I bow my head and bring that pencil to the page. I write facts; facts that I suppose to be true. I lead those facts through numerical processes into other facts. ‘Therefore’ is a symbol of three dots in the form of an equilateral triangle. Truth equals truth equals truth.

 I start with the easy things: the loads. How much do things weigh? I weigh a kilo newton. There might be four of me in a square metre. I put these all down. Page one is filled. Then the system: I call it the system. I copied this idea from someone else, 20 years ago. I draw a little sketch. Beams and columns and slabs feature. Some dimensions. References: beam A beam B. And then the ‘design’: the maths. The strength and then the deflection. Strength is most important but easier to prove. Strength failure means dangerous collapse. Deflection and resonance are elusive but obvious on the finished structure. This is the grey area between known fact and the incomprehensibility of behaviour. This is where I have to start to think about how I might behave if I were a beam or a slab. How a piece of paper might twist in my fingers, or how a fishing rod or a spline might flex. I have to find numbers for this and put them down so someone else can follow them.

 

This is where I have to start to think about how I might behave if I were a beam or a slab. I have to find numbers for this and put them down so someone else can follow them

 After so many years I have convinced myself I can feel these things. As I get older I get vaguer and more complacent. I forget names and faces, dates and appointments. But I’m still a sharp calculator. My capacity for mental arithmetic has grown wildly. Sometimes I believe I can feel how one beam hands loads to another; how another beam transfers movements; how its flex allows another beam to flex. But I also know this instinct vanity is conjectural and flawed. 

I have to enumerate.  I calculate the loads, the bending moments, the shears and then I choose components to resist them. I use codes, formulas and first principals. As the design becomes more complex my handwriting becomes looser and what’s more, I’m rushed: I have to finish. There’s a fee to consider. The bold figures start to become scrawny, many times erased. Those three dots draw conclusions that many may question. Reason and hunch are deployed. 

Off the paper, I draw up contingency plans. If I’m wrong, then this will happen which will still be ok. Safety factors, redistribution of forces, restoring effects. I’m proud of a skinny beam and a thin slab: ego. I won’t over design. I reach a conclusion but I have reservations. 

I’m a climber. Not a good one, but nonetheless a courageous trad climber. I rise on an escarpment with my rope, placing chocks and bolts into cracks: climbers are cautious, they make many provisions to safety. When I’m calculating I’m quite often flamboyant, but then I think about this: I think I’m climbing. I try to envision the jeopardy of others. I try to impose a fear on myself that a person in a desk sitting over a pad cannot easily feel. But I’ve done the numbers. I believe in the numbers. I’ve performed the act of calculation. 

Steve Webb is a structural engineer and director at Webb Yates Engineers and Interrobang