Posted by: Grandma LaLa | October 26, 2014

Top 4 learnings from the FNAL lecture: engineering

14-10-24 FNAL lectureEngineering isn’t my thing.  So the FNAL lecture by Henry Petroski (civil engineering and history professor from Duke University) wasn’t on my list of must-attend public events.  But Ron and Dad were both interested, so we put the date on our calendar.  As it turned out, Ron wasn’t able to go, but Dad, Dick, and I really enjoyed the lecture.

“Success and Failure in Engineering: a paradoxical relationship” addressed case studies on the premise that failures in engineering help scientists to structure better successes ~ and successes in engineering often lead to over-confidence that eventually results in failure.

1.     the Titanic – mechanical engineering

Engineers designed this ocean-going vessel with massive steel plates, riveted together. They anticipated that the ship could survive a head-on collision with an iceberg, but apparently didn’t think in terms of a side grazing by an iceberg.  Just such an event on the Titanic’s maiden voyage tore a gash along the side, with water pressure then “unzipping” the rivets and plates.  Internal structure played a factor too.

This engineering failure occurring on the ship’s first journey helped engineers and ship-building businesses to avoid further failures, which might have included: assuming structural soundness and building with thinner steel plates and/or fewer rivets; carrying too few lifeboats; carrying more passengers; continuing the pattern of turning off on-board radio communication at night.

2.     suspension bridges – civil engineering

Suspension bridges in the 19th century helped to span greater expanses of water, without interfering with boats, ships, and other water-faring vessels.  But the chief problem for any suspension bridge is sustained wind and/or storms, in which the expanse between the anchoring structures tends to sway.

Petroski used examples to demonstrate that there isn’t just one way to resolve these engineering problems.  British and European engineers tended to design massive tube bridges (heavy, expensive to build, and environmentally unfriendly when soot from a locomotive belched into the tunnel and back into the open-air coach seats).  American engineers, led by John Roebling, built wider bridges (with more weight/mass), reinforced with trusses and diagonal stabilizing cables to help stabilize the structure in sustained wind.

As new bridge designs evolved over the past century, some suspension bridges in the US were constructed without trusses and/or without the diagonal cables.  Forgetting the various engineering lessons of the past century, some of those bridges failed.  Some failures due to unevenly distributed weight, such as heavy construction trucks standing on one side and stress unevenly distributed.  Some failures (impending) due to lack of sufficient stabilizing cables, which is already showing wear on the few existing cables.

As a result of these civil engineering failures that seem to have forgotten or dismissed some of the insights from the past, these designs are now pretested in wind tunnels

3.     tall buildings – structural engineering

In the question and answer period, someone asked about a particularly large building.  Petroski discussed this briefly, suggesting that most of the issues about large buildings are less about engineering and more about human inhabitants.  For a proposed building that is a half-mile wide, a half-mile deep, and a half-mile high, the first issue would be that a large number of elevators would be needed.  This could easily consume one-third of the cubic space.  Developers aren’t likely to want to devote that much space to structural features that don’t generate income.  The second issue would be that most people in offices or residences want windows.  Again, in a structure that large, most of the tenants would have internal spaces without windows.

This led him to reflect upon the engineering process prior to the construction of one of the world’s tallest towers.  Engineers wondered how much building movement people could/would tolerate on upper floors, since the structure would sway by feet and even meters.  So they created a “blind” test in which individuals were offered free eye exams.  These test subjects came into a room for the exam, while the engineers behind the scenes actually moved the room itself.  This helped to establish how much movement people notice, as well as how much we can tolerate.  Interesting!

4.     engineering as learning

It wasn’t really on the topic of successes and failures, but one of the audience questions related to the new initiatives to introduce more STEM (science, technology, engineering, and math) into the K-12 curriculum.  The person asked what Petroski recommended in terms of engineering for K-12.

He duly noted that he doesn’t really teach children of those ages and isn’t familiar with current curricula.  But he suggested that the chief gift of learning for engineering would be problem-solving in which there isn’t (just) one correct answer, but possibly many.  Good answer!


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