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Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

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A.2 Group Interaction FactorThe cross section <strong>of</strong> all piles used for <strong>the</strong> <strong>Bill</strong> <strong>Emerson</strong> <strong>Memorial</strong> Cablestayed<strong>Bridge</strong> is round. Therefore <strong>the</strong> stiffness and damping coefficients <strong>of</strong> anyindividual pile are <strong>the</strong> same in any horizontal direction. In a pile group, however,<strong>the</strong> number <strong>of</strong> piles in x and y directions may be different. As a result, <strong>the</strong>stiffness and damping coefficients <strong>of</strong> a pile group depend up on <strong>the</strong> number <strong>of</strong>piles and <strong>the</strong>ir spacing in each direction.To study <strong>the</strong> group effect, Paulos (1968) considered one pile in <strong>the</strong> groupas a reference. For example, in Figure A.4, No. 1 is assumed as a reference pileand distance ‘S’ is measured from <strong>the</strong> center <strong>of</strong> any o<strong>the</strong>r pile to center <strong>of</strong> <strong>the</strong>reference pile. If <strong>the</strong> effect <strong>of</strong> <strong>the</strong> reference pile is considered as 100%, that <strong>of</strong>any o<strong>the</strong>r pile is reduced by an interaction factor α A for vertical vibration and αLfor horizontal vibration. The interaction factor α A can be determined from FigureA.5 based on <strong>the</strong> length <strong>of</strong> pile (l) and <strong>the</strong> radius <strong>of</strong> pile section (r o). The factor αLcan be obtained from Figure A.6 for each pile, taking into account <strong>the</strong> departureangle β in degree (Paulos, 1972). The factor α L is a function <strong>of</strong> l, rK R as defined in Figure A.6.o, and flexibilityFigure A.4 Plan and cross section <strong>of</strong> pile group103

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