ch1-Introduction

ch1-Introduction - Early structural concepts Some of the...

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Early structural concepts Some of the structures in earlier have endured for ages. Materials used were brittle type like bricks, stones, mortar: poor to carry tensile loads. Avoided fracture possibilities by selecting appropriate geometric shapes like arches, domes The structure were designed to carry load by compression New structural concepts Availability of metals lead to change in structural concepts: allowed tension in structure. (this invited additional problems like fracture) Designs based on strength allowed a factor of safety ranging from 2 to 10, but still structures failed by sudden brittle fracture Eg. 1919 rupture of Molasses tank in Boston * When ever there is new material or new design concepts produces unexpected results leading to catastrophic failure
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Hogging Bending Moment 1943, Liberty ship : a cargo ship Prior to II world war liberty ships were riveted (very slow process) having no fracture problems During war, to accelerate ship building, England sought help from USA. USA companies offered to build ship faster, by welding joints. They maintained same geometric shape, ship hull turned out to be a single envelope of steel. Ships were sailing across Atlantic and Artic ocean. (cold temperatures). During which two ships fractured suddenly in to two halves ( brittle fracture). Out of 2700 ships built, 400 ships suffered fractures of various degree. Analysis Unequal distribution of cargo and ballast was causing hogging bending moment Wave motion also caused hogging BM, resulting in tensile stress on the deck. Welds were produced by semi skilled work
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This note was uploaded on 12/11/2011 for the course EML 3004c taught by Professor Staff during the Fall '11 term at FSU.

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ch1-Introduction - Early structural concepts Some of the...

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