At least once a year, I participate in middle school career fairs to talk about being a bridge engineer. While I have many stories I find interesting and enjoy my career and the challenges of each day, I do not want to bore the students. So I developed a fairly simple exercise that I have been doing with each group of students.
I ask for 2 volunteers to help me design the best bridge for this location – which is just a box but could represent any of the thousands of bridges that need to be designed. See photo 1 for the working materials which includes various sizes of wood, a steel tube, a brick, and a cardboard tube.
So which would you choose? Invariably, the students pick the 2×4 which reaches across the span, is wide and very sturdy. Then I tell them there are 4 criteria for evaluating if we have the best bridge. After some enthusiastic guessing and a minor amount of coaching we come up with the following list
Back to the 2×4 bridge – it is strong and safe but is it the most cost effective? After a brief discussion on taxes and the cost of building bridges, we decide that cost is important and I encourage them to look at other options. Usually the other pieces of wood and the steel curtain rod are tried until the thinnest one is declared unsafe because it is too flimsy. Then we try putting a brick in the middle as a support in the middle of the bridge (we call them piers) or use the paper towel roll as a pier. Piers can be costly to build and can be an obstruction that gathers debris during storms. The paper towel roll would be very cheap but it would not be durable (the 4th criteria).
Now the real bridge engineer steps in and asks them to consider placing two of the cheap, flimsy (but durable) pieces of wood on end with some supports between them so they do not buckle. Now we have a bridge that meets the 4 criteria and the “best” bridge for this exercise. However, without a bridge engineer to analyze and calculate (using the math and science skills taught in school and later college) that the bridge meets these 4 criteria, we would likely end up with a bridge that is either more costly than it needs to be, or unsafe, or will not last long.
Engineers, not just bridge engineers, bring stability to our world as we take seriously our responsibility for the safety and well-being of the public we serve. We need to continue to raise up new generations of leaders that accept this responsibility, so that is why I will continue speaking at career fairs (plus it is fun to play with blocks of wood for a few minutes)!