DAM FAILURE BLAMED ON DESIGN : ENGINEERS STUDY FOLSOM GATES TO PREVENT BREAKS AT SIMILAR FACILITIES.Byline: Nancy Vogel Scripps-McClatchy Western Service
Eight months into an investigation of why a spillway spillway,
n a channel or passageway through which food escapes from the occlusal surfaces of the teeth during mastication. The occlusal, developmental, and supplemental grooves, as well as the incisal, occlusal, labial, buccal, and lingual embrasures, gate at Folsom Dam Folsom Dam is in Northern California about 25 miles northeast of Sacramento on the American River. The dam is in Sacramento County and forms Folsom Lake. Folsom Dam is a concrete gravity dam, which depends on its weight to hold back the lake. broke last summer, engineers say hidden corrosion and weak design are likely culprits, not the rusted beams and bolts noted by inspectors before the accident.
A final report is months away, and tests continue. But members of the forensics See computer forensics. team trying to figure out how and why Gate No. 3 broke after 41 years of good service say the trigger may lie in the two big pins, called trunnions, that pivot the garage-doorlike gate up and down.
Some team members theorize the·o·rize
v. the·o·rized, the·o·riz·ing, the·o·riz·es
To formulate theories or a theory; speculate.
To propose a theory about. that the grease the bureau had been using in the pins broke down or squished out. Moisture invaded, corrosion ensued, and at 8 a.m. July 17, as an operator pushed the gate's ``up'' button, the pin might have jerked with enough force to shear bolts.
That force, and water rushing under the gate, may have set the 88-ton gate into destructive vibration, engineers say. Two of the gate's steel arms, or struts A framework for writing Web-based applications in Java that supports the Model-View-Controller (MVC) architecture. Struts is deployed as JSP pages using special tags from the Struts tag library, which includes routines for building forms, HTML rendering, storing and retrieving data and , fell off the dam. One hung on by an end. The fourth crumpled crum·ple
v. crum·pled, crum·pling, crum·ples
1. To crush together or press into wrinkles; rumple.
2. To cause to collapse.
1. , and the gate swung open like a hinged door.
``The gate literally vibrated itself to failure,'' said Tom Aiken, area manager for the U.S. Bureau of Reclamation Reclamation
A claim for the right to return or the right to demand the return of a security that has been previously accepted as a result of bad delivery or other irregularities in the delivery and settlement process. .
A five-story wall of water shot out of the dam, about 20 miles northeast of Sacramento. No one downstream was hurt, but the bureau had to release enough water to supply 2 million people for a year before the pressure against the dam eased enough for them to block off the gate. Since then, Gate No. 3 has been lifted out and the other seven gates have been reinforced, with more work scheduled.
Around the world, people who operate hundreds of Folsom Dam-style gates, called ``radial radial /ra·di·al/ (ra´de-al)
1. pertaining to the radius of the arm or to the radial (lateral) aspect of the arm as opposed to the ulnar (medial) aspect; pertaining to a radius.
2. arm'' gates, await the bureau's forensic report. California's dam safety office has notified 58 radial gate operators to begin extensive inspections. One of them, the Santa Clara Valley Water District The Santa Clara Valley Water District provides stream stewardship, wholesale water supply and flood protection for Santa Clara County, California, in the southern San Francisco Bay Area. , already has decided to replace two corroded cor·rode
v. cor·rod·ed, cor·rod·ing, cor·rodes
1. To destroy a metal or alloy gradually, especially by oxidation or chemical action: acid corroding metal. gates at Vasona Reservoir.
``This is why we're being so careful on this forensics report,'' said Aiken, ``because it goes way beyond Folsom Dam.''
A preliminary report is due in a couple of weeks, with a final report expected by June.
Engineers say it's clear now that the steel arms that brace the gate were designed without sufficient strength.
John White, chief of structural design for the U.S. Army Corps of Engineers, scrutinized Folsom Dam's original designs and found that the designers, working without computers, did not take into account friction in the trunnions when deciding how heavy and strong to make the arms, or struts.
``The designers met the original criteria in effect at the time,'' said White. Before the Gate No. 3 failed, Folsom's gate struts did not meet current standards. They do now, as last fall bureau contractors bolstered each of seven gates with 22,000 pounds of steel.
Gate No. 3 is blocked by steel beams and should be replaced by March 1997.
Around the country, said White, it's likely that other gates will have to be strengthened as at Folsom.
Engineers also say they believe that beam and bolt corrosion, as noted by inspectors in 1988, 1991 and 1994, played a minor role in the accident. For lack of money, those repairs were not made until after the gate broke.
``It might have had a factor of 7 percent in terms of causing the failure,'' Aiken said, noting that some of the most-corroded beams held.
In a warehouse at the dam, engineers are now using the pin from the broken gate to test different types of grease. What they're finding, said White, is that some of the brands of extreme-pressure grease the bureau used in recent years were not as effective as the lead-based grease that was phased out in the 1980s.