Lecture03-Types-of-Foundations

Lecture03-Types-of-Foundations - Foundation Foundation...

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Foundation Foundation Engineering Engineering Lecture Lecture #03 #03 Types of Foundations How are they selected? L. Prieto-Portar 2009
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Introduction. A thorough geotechnical investigation will usually suggest the ideal type of foundation to be used at a site. This implies functionality , safety and cost effectiveness . Usually, the final report will suggest the best two alternatives. Typically, a structure is primarily designed for function . Artistic works are, for example, the opposite to that criterion. After the criterion of functionality is satisfied, then the two subsequent criterions considered by the designer are its aesthetics and its structural requirements . Finally, after all these are satisfied, foundations are accommodated around the above constraints. Rarely are foundations considered at the outset. xceptions are in seismic severe areas, and in predominantly civil works, such as earth Exceptions are in seismic severe areas, and in predominantly civil works, such as earth dams, deep excavations, tunnels, bridges, etc. The influence of foundations has existed since prehistoric times, and become notable in Chaldean and Egyptian public works. In contrast, most Greek monuments, so influential to modern architecture, ignored the fine foundation experience developed by older builders, primarily because the Greeks benefited from their peninsula's excellent surface rocks. Even with an excellent rock subgrade, most Greek structures have collapsed compared to the still existing Roman bridges, aqueducts and buildings.
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The structural solution of a structure must consider the behavior of the soil over long periods of time. For example, a tall reinforced concrete building behaves poorly in consolidating clay, when compared to a more flexible steel structure. Foundations must therefore be visualized as a natural connection between the structure and the soil, minimizing poor connectivity. For example, the use of basements should be viewed both from a geotechnical and a space requirement points of view. The designer should answer these questions: 1. Is the rock shallow? Does it require blasting? 2. Is the bearing stratum within 4 meters from the surface? These 4 meters are easily reachable if you had planned for a basement, but expensive otherwise. Also, a basement may wipe out a good surficial stratum, forcing the use of deep foundations. 3. In very soft ground, use a floating or compensated mat foundation. The economics of a compensated mat suggests the use of one basement per each six stories of building height. However, two or three levels below the water table may require the use of expensive cut-off walls.
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The Type of Building. The average cost of a foundation for a multistory building ranges from 3 to 8% of the construction cost. Special structures, however, or difficult soils may raise the cost to 20% or higher. Light structures, such as 2 or 3 story buildings can be supported on inexpensive shallow foundations. Taller buildings might require more expensive
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Lecture03-Types-of-Foundations - Foundation Foundation...

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