Group 14 Jerrod Stock David Villers

 Location: between Tacoma and Gig Harbor, Washington  Total Length: 5,939 ft.  Longest Span: 2,800 ft.  Width: 39 ft.  Clearance: 195 ft.  Construction: Sept. 27, 1938  Opened: July 1, 1940

 Original plan made by Clark Eldridge - $11 million.  Redesigned by Leon Moiseiff with drastic modifications - $7 million.  Significant Modifications: 25 ft. deep trusses replaced by 8 ft. deep girders.  Bidding contractors complained about revised foundation piers. Original plans were shown, and they agreed.

 “Creative Techniques” were used → packing girders with dry ice.  One death during construction.  “As soon as floor forms were started, oscillation occurred.”  Nicknamed “Galloping Gertie”

 Tie-down cables from girders to 50-ton concrete blocks → snapped after installation.  Pair of inclined cable stays connected main cabled to deck at mid-span → ineffective.  Hydraulic buffers between towers and deck floor system → seals damaged when bridge was sand-blasted before painting.

 Washington Toll Bridge Authority hired Professor Frederick Farquharson.  Conducted wind-tunnel tests on 1:200-scale bridge and 1:20-scale deck section models.  2 Solutions:

 November 7, 1940 – 40 to 45 mph winds  7AM – Bridge begins transverse vibrations (3 ft. amplitude).  10AM – North cable collar loosens; violent torsional oscillations begin (28 ft. amplitude).  10:30AM – Bridge begins cracking.  11:10 AM – Center span collapses.

 One fatality:

 aV4 aV4

 Convinced contractors to bid by showing plans for foundation piers that weren’t part of decided design.  Moisseiff’s design was new and hadn’t been modeled and tested:  8 ft. girders meant shallow roadway sections → bridge deck was insufficiently rigid.  Flat outward facing surfaces of girders weren’t aerodynamic.

 Rejected initial conventional design based solely on cost.  Chose unproven design which had insufficient research. Combined Ethical Issue:  Opened bridge to public despite:  Oscillations which they knew would have to be fixed.  Early failure of vibration control systems.

 Used a standard and proven design rather than the new “elegant” design.  Halted new design acceptance until a scale model was built and passed testing.

 Shut bridge down or delayed opening until permanent solution was reached.  Replace hydraulic buffers to help stable bridge for construction of permanent fix.  Expedite Professor Farquharson’s research.  Then expedite implementation of determined solution.

 Safety of users  Mechanical parts could cause injury:  Motors, gears, springs.  Prevention: Inner workings of devices are in sealed location. Necessary user input devices are away from moving parts.  Predictability of projectiles Prevention: Both automatic timed shut off and manual stop button.

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