101 Things I Learned in Engineering School
by John Kuprenas with Matthew Frederick
Engineering involves the application of mathematics, physics, and chemistry, but “the heart of engineering isn’t calculation; it’s problem solving,” writes John Kuprenas, a civil engineer. Here is a sampling of his insights.
“Accuracy is the absence of error; precision is the level of detail. Effective problem solving requires always be accurate, but being only as precise as is helpful at a given stage of problem solving. Early in the problem solving process, accurate but imprecise methods, rather than very exact methods, will allow consideration of all reasonable approaches and minimize the tracking of needlessly detailed data.”
“There’s always a trade-off. Lightness versus strength, response time versus noise, quality versus cost, responsive handling versus soft ride, speed of measurement versus accuracy of measurement, design time versus design quality… It is impossible to maximize the response to every design consideration. Good design is not maximization of every response nor even compromise among them; it’s optimization among alternatives.”
“An object receives a force, experiences stress, and exhibits strain…
- A force, sometimes called “load,” exists external to and acts upon a body, causing it to change speed, direction, or shape. Examples of forces include water pressure on a submarine hull, snow loads on a bridge, and wind loads on the sides of a skyscraper.
- Stress is the ‘experience’ of a body—its internal resistance to an external force acting upon it. Stress is force divided by unit area, and is expressed in units such as pounds per square inch.
- Strain is a product of stress. It is the measurable percentage of deformation or change in an object, such as a change in length.”
“An object that receives a force will remain stationary, move, or change shape—or a combination. Mechanical engineering generally seeks to exploit movement, while structural engineering seeks to prevent or minimize it. Nearly all engineering disciplines aim to minimize changes in the shape of the designed object.” The book also explains four characteristics of materials: stiffness/elasticity, strength, ductility/brittleness, and toughness.
“Steel and concrete have near-identical coefficients of thermal expansion: if they did not, a steel-reinforced concrete beam would tear itself apart upon ordinary temperature change. More often, materials are not neutral toward each other,” as the following story illustrates. “Monel metal is a very hard alloy of nickel, copper, and iron. It is extremely corrosion resistant and is excellent for wet applications. However, in 1915, a ship was built with a hull entirely on Monel, with the expectation of an exceptionally long life. Unfortunately, the 215-foot-long, 34-foot-wide Sea Call had to be scrapped after six weeks of use. The Monel hull was fully intact, but the steel frame of the ship deteriorated beyond use, from electrolyte interaction with the Monel in the saltwater environment.”
“A triangle is inherently stable. A triangle differs from other linear shapes in that its sides and angles are interdependent: a change cannot be made to an angle without altering the length of at least one side, and vice versa. By comparison, a square can be deformed into a parallelogram without changing a side… A truss is a complex form of beam that takes advantage of the inherent stability of the triangle. By starting with a triangle and adding two legs at a time, a series of interdependent triangles form a stable structure capable of spanning long distances, using a fraction of the material used by an ordinary beam.”
“A skyscraper is a vertically cantilevered beam. The primary structural design challenge of a skyscraper is not resistance to vertical (gravity) loads, but resistance to lateral loads from wind and earthquakes. For this reason, tall structures function and are designed conceptually as large beams cantilevered from the ground.”
“Concrete doesn’t dry; it cures. Concrete gains its strength through a chemical reaction between cement and water. After pouring, concrete is often kept wet for an extended period to prolong the chemical reaction (thereby strengthening the product), and to keep outer portions of the concrete from drying long before interior portions (thereby minimizing cracking). Design calculations for concrete construction typically are based on the strength expected after 28 days of curing. However, the maximum strength of a very large pour might not be achieved for decades… Cement is a hardening ingredient in concrete, and is usually derived primarily from limestone.”
“Stop a crack by rounding it off. Crack propagation in a material increases with the sharpness of the tip of the crack. Drilling a hole at the tip makes a crack less sharp and distributes the stresses over a larger area and in more directions, discouraging the crack from lengthening. Rounded corners in building products, machine parts, furniture, and even windows of ships and airplanes provide similar benefit. A rounded window corner spreads stress in multiple directions, while a sharply squared corner directs stress through one point in the system—crucial consideration in the design of a ‘thin-shell’ structure.”
“Air is fluid. A fluid is any amorphous substance that yields easily to external pressure and assumes the shape of its container. This includes all gases and liquids.”
“Heat cannot be destroyed, and cold cannot be created. An air conditioner doesn’t create cold, but moves heat from a building interior to the exterior. It does this by exploiting a natural principle: substances absorb heat when moving from a liquid phase to a gas phase, and release heat when moving from gas to liquid.”
“At the point a designer is invited into the design process, many assumptions have been made about the nature of a problem, and the desirable solutions. The wise designer begins by moving backward—investigating what caused the problem, what caused the causes, and what caused those causes. This reveals possibilities that might be very different from what the end user anticipated, but that meet the true need most effectively.” This reminds me of the five-why analysis discussed in The Toyota Way.
“Think systemically. A system must be analyzed as a whole, but analysis of the whole is not the summation of the analysis of its parts. The behavior of a part is not constant, but depends on its relationship to the system in which it resides. And the behavior of the system depends on the many relationships within it, and on the system’s relationship to other systems. Thinking systematically means employing a given thinking method consistently and thoroughly. Thinking systemically means thinking about systems and connections—the web of relationships within a system, the relationship of the system to other systems, and the larger system that contains all the systems.”
The book provides a good selection of concepts for prospective engineering students, especially those interested in civil and structural engineering. The title not only refers to the number of items presented, but is also a word play (intentional or not) on the introductory course number Engineering 101.
Kuprenas, John, and Matthew Frederick. 101 Things I Learned in Engineering School. Boston: Grand Central Publishing, 2013. Buy from Amazon.com