Presentation on theme: "Group 14 Jerrod Stock David Villers. Location: between Tacoma and Gig Harbor, Washington Total Length: 5,939 ft. Longest Span: 2,800 ft. Width:"— Presentation transcript:
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.
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.