The Importance of Performance- Based Geotechnical Parameters for Nonlinear Analysis
ABSTRACT:
Traditional geotechnical engineering practice typically utilizes a wide variety
of empirical correlations which contain varying degrees of epistemic and
aleatory uncertainty. The source of the uncertainty varies from the use of
poorly controlled field test methods to sample disturbance prior to laboratory
testing. When accounting for uncertainties such as these, the geotechnical
engineer may be influenced by a desire to give "conservative" values or "better"
values to the structural engineer. However, when considering performance-based
design, rather than accounting for the uncertainties in empirical formulae and
test results through the use of poorly understood and inconsistently applied
factors of safety, there is a need for a reduction in the uncertainties
themselves. This can be accomplished through the use of high quality field and
laboratory testing methods. It is important that the uncertainties in the
geotechnical parameters are reduced and that arbitrary safety factors not be
applied so that the actual performance of the structure can be accurately
modeled by the structural engineer. The best estimate of geotechnical.
performance is what is required. Overly conservative or overly aggressive
foundation stiffness and/or bearing capacity values, which may seem desirable to
some engineers, can lead to the incorrect predicted failure mechanism of the
structure and result in a misguided retrofit scheme. Accurate estimates of
geotechnical parameters and reduced uncertainties can help owners build safety
and cost savings into the analysis and retrofitting of existing buildings. A
case history is presented where performance-based design concepts were utilized
in obtaining geotechnical parameters for the nonlinear analysis of an existing
hospital building.
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