...CHAPTER I INTRODUCTION Background of the Study Structural materials can be categorized in many ways in many different ways. One of the most common is by the nature of their failure. Materials, such as steel, after reaching their elastic limit, deform plastically before failing. Such materials, where reasonably large plastic strains are observed, are broadly categorized as ductile. On the other hand, those materials that exhibit little or no plasticity are in contrast termed brittle. In structural design, ductile materials are usually preferred, because failure is rarely sudden and catastrophic. Once the material has yielded, large observable strains will occur before total collapse of a structure. Steel, the most common primary structural building material, generally behaves in a ductile fashion. However, during the World War II, over 200 steel ships suffered serious brittle fracture, often at relatively low stress levels. It was observed that brittle behavior, in normally ductile materials, almost always occurs in regions of elastic stress concentration, where some constraint exists to prevent plastic stress redistribution (McGuire, 1968) Following these experiences, designers realized that brittle fracture in steel could be avoided by sensible detailing. This is also true of reinforced concrete. Concrete itself, is a brittle composite, but with the addition of reinforcements concrete it behaves in a ductile fashion. In an earthquake-prone areas, where designing for ductility...
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