EAS 140 Engineering Solutions Lecture #27 How Engineers Learn from Failure

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Announcements – A, B  Mon. 12/3: Lecture - Lessons from Failure  Wed. 12/5: Lecture - Course Review  Thurs. 12/6: In-lab quiz for Thursday labs  Mon. 12/10: Final Examination –Will make sample questions available after Thanksgiving –Will emphasize material from lecture and case studies; no computing from lab

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Announcements – C  Tues. 12/4: In-Class Ethics Case Study  Thurs. 12/6: Lecture - Lessons from Failure and Course Review –In-lab quiz for Thursday labs  Mon. 12/10: Final Examination –Will make sample questions available after Thanksgiving –Will emphasize material from lecture and case studies; no computing from lab

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Announcements - D  Wed. 12/5: Lecture - Lessons from Failure  Thurs. 12/6: In-lab quiz for Thursday labs  Fri. 12/7: Course Review  Mon. 12/10: Final Examination –Will make sample questions available after Thanksgiving –Will emphasize material from lecture and case studies; no computing from lab

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Learning from Failure - Overview  Engineers design systems so that systems will fail –Remember: too expensive to design a building so it will never fall down  But… Sometimes systems fail before we intend for them to fail  Although sometimes tragic, engineers must learn from such failures

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Why Do Engineered Systems Fail?  Many Reasons for Failure – ideas from class?  Engineer’s Error –Kansas City Hyatt Regency –Mars Climate Orbiter (see text)  Warning Signs Ignored –Space shuttle Challenger evidence of a leaking o-ring at low temperature ignored  Cycle of Overdesigning and Underdesigning –Will discuss in more detail

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Overdesign/Underdesign Cycle  Because consequences of failure are high, engineering is a conservative discipline  Most “first attempts” are overdesigned –Example: In structural engineering, this means that the capacity is much, much greater than the load  Capacity is removed in subsequent systems – why? –save money, looks better  Eventually, system is unstable and failure occurs  Cycle restarts with overdesigned systems

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Example – Suspension Bridges  What is a suspension bridge? –Roadway is suspended on cables –Cables pass over high towers –Towers are anchored in the bedrock  Example: Golden Gate Bridge

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Example – Suspension Bridges  Failure Modes –Suspension bridges are susceptible to failure from wind loading –Can oscillate in the wind  Solution –Key design factor is the ratio of the depth of the girder to the length of the span between the towers span length girder depth

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Example – Tacoma Narrows Bridge  Statistics –Completed: 1940 –Span length: about 2800 ft –Third longest suspension bridge in the world when built –Built over a very windy “narrows” in Puget Sound  Design –To make the bridge appear slender, used a very small girder depth-to-span length ratio –Ratio was about one-half of the ratio for the Golden Gate Bridge

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Example – Tacoma Narrows Bridge  Result: –Called “Galloping Gertie”  Four months after construction: Click me

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Example – Tacoma Narrows Bridge  Aftermath: –When reconstructed, greatly increased the depth of the girders –Note how deep the girders are

Chemical  Civil  Computer  Industrial  Electrical  Mechanical EAS 140: Engineering Solutions Overdesign/Underdesign Cycle - Summary  Overdesign at first  Underdesign later to save money or for aesthetics  System becomes unstable and failure occurs  Cycle restarts with overdesigned systems