Model Uncertainty of Eurocode 7 Approach for Bearing Capacity of Circular Footings on Dense Sand

Abstract

This paper presents a critical evaluation of the model factor M = qu,m/qu,c for Eurocode 7 calculating the bearing capacity of circular footings on dense sand, where qu,m = measured capacity and qu,c = Eurocode 7 calculated capacity. Regression analysis is required to remove the dependency of M on the input parameters. Because the input parameters cannot be varied systematically in load tests, previous studies showed that finite-element limit analysis (FELA) can be used as an alternative to load tests for regression. This is further verified from the model factor MFELA = qu,m/qu,FELA with a mean of 1 and a coefficient of variation (cov) of 0.1, where qu,FELA = FELA predicted capacity. A correction factor (Ms = qu,FELA/qu,c) is next defined, which can be decomposed as a product of a systematic part f and a residual part η (i.e., Ms = fη), which is modeled as a lognormal random variable with mean = 1 and cov = 0.11. Finally, a new model factor (M′ = qu,m/q′u,c = qu,m/fqu,c) is defined. The model statistics of M′ = ηMFELA can be obtained from those of η and MFELA, where mean = 1 and cov = 0.11. This is consistent with the results (mean = 1.02 and cov = 0.15) characterized using the load-test database directly, because M′ no longer depends on the input parameters.