ABSTRACT:

Resistance factors of the conventional load and resistance factor design (LRFD) are calibrated from reliability analyses using the load and resistance distributions. In pile design practices, proof pile load tests are conducted to verify the pile designs. Typically, proof pile load tests are performed until an axial load on the pile head reaches twice its design load. Considering that the piles are usually designed with factors of safety higher than 2.0 (typically, 3.0), pile failures are rarely observed during proof pile load tests. When installation of a large number of piles is scheduled within a certain site, at least several proof pile load tests are required. For a given certain site, the proof pile load test results, indicating how many failures observed out of the total number of proof pile load tests, can be regarded as valuable information reflecting the site characteristics. This information can be quantified by a certain equation, which is a likelihood function. Bayesian theory for the obtained likelihood function enables updates of the conventional resistance factors. Based on the pile load test database collected from Korea sites, the site-specific adaptive resistance factors calculated from Bayesian theory implementation varied within wide ranges of 0.27 to 0.96 and 0.19 to 0.68 for target reliability indices of 2.33 and 3.0, respectively, depending on the proof pile load test results.

INTRODUCTION

LRFD approach requires that the load and resistance factors be defined in the framework of reliability theory based on the statistics of the measured-to-predicted values of the loads and resistances. Selection of sets of load factor values for different load combinations has been well defined in current structural practice. Therefore, LRFD in structural engineering has been successfully implemented through the calibration of resistance factors for the specified set of load factors and load combinations.

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