FEA builds a better barge

April 1, 2005
FEA showed a team of nautical engineers where a barge model was overdesigned so they could remove material and still let it safely handle the high loads it will encounter.

The barge carries a 180-ton excavator that can lifts soil from the sea bottom at a depth of 16 meters and deposits it onto other barges, also designed and fabricated by Cordoba's team.

The barge consists of the main platform (including the shell plate, deck plate, bottom, and bulkheads), modeled with 8-mm-thick plate elements.

"What's more, we delivered fabrication drawings of the barge's spud legs to our shop less than one month after obtaining the FEA software," says Eddy Cordova, structural projects chief designer at Servicios Industriales de la Marina in Peru. A spud is a sharp-pointed vertical post that anchors a platform to the ocean floor. Fabrication drawings for the barge were delivered in less than two months and the manufactured vessel delivered to the customer in four.

Cordoba's team uses software from Algor Inc., Pittsburgh, because of their confidence in the software's meshing and analysis capabilities. Cordova learned to use the software from keystroke tutorials, two Spanish-language distance-learning courses, online documentation, and customer service. "I used the software several years ago. But the Fempro user interface makes the current version even easier to use," he says.

The team created finite-element models of the barge's structure and several high-load zones such as bulkheads and spud legs. Linear-static stress and critical buckling-load analyses determined how the design would withstand the expected loading. "The spud legs were of particular concern because they are large tall structures that have to carry high loads 24 hours per day," he says. The three spud legs combined carry up to 340 tons.

The team examined several load combinations and constraints that varied the number of pinned spuds, excavator position, wave position, sea height, and the wind direction. "We determined the critical load combination and were able to reduce the thickness of several spud plates from 19 to 12.5 mm for 9.0 m of the spud length while maintaining structural integrity. This significantly reduced the amount of steel needed." A critical buckling-load analysis verified that the spud leg would not buckle. "Algor FEA lets us quote and design new projects faster, optimize existing designs, and design steel structures with less weight compared to previous versions," says Cordova.

Algor Inc.

(412) 967-2700
SIMA Peru S.A.

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