Chap. 2Uncertainty and Risk in Foundation Design2.1Classify the uncertainty associated with following items as either aleatory or epistemic andexplain your reason for your classification: average wind speed over a 30 day period, location ofa certain applied load, change in strength of a soil caused by sampling method, capacitydetermined by a certain analysis method, magnitude of live load caused by vehicles travelling ona bridge, soil shear strength as measured by a certain method.Solution•Uncertainty of the average wind speed is aleatory.This is a random process that wecannot affect.•Uncertainty of location of an applied load is mostly aleatory. There is a certain accuracywith which a structure can be built and the designer had little or no control over thisaccuracy.In theory there is some epistemic uncertainty in that could be reduced withbetter construction techniques, but from a practical standpoint this uncertainty is aleatory.•Uncertainty in the change in strength of a soil caused by sampling method is an epistemicuncertainty. Improved sampling techniques can reduce this uncertainty.•Uncertainty in the capacity determined by a certain design method is generally epistemic.With improved analytical tools we can reduce this uncertainty.•Uncertainty in magnitude of live load caused by vehicles travelling on a bridge isinherently aleatory. This is a random process which we cannot affect.•The uncertainty in the soil shear strength asmeasured by a certain method is acombination of epistemic and aleatory uncertainty. The uncertainty caused by the qualityof the equipment used and the care of the technician making the measurement isepistemic and can be reduced by the use of more precise equipment and better training ofthe technician. However, there is aleatory uncertainty in the soil strength inherent in thenatural processes that created the soil.Solutions ManualFoundation Engineering: Principles and Practices, 3rdEd2-1Preview Mode
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