사질토 지반 얕은기초의 목표신뢰도지수 및 저항계수 산정

Abstract

Load and Resistance Factor Design(LRFD) is one of the limit state design methods and has been used worldwide in civil engineering designs, especially in North America, Asia, and other developing countries. Accordingly, the studies on LRFD has been actively conducted in Korea. However, the data for LRFD in Korea were not sufficient to perform statistical and reliability analyses, so resistance factors suggested by American Association of State Highway and Transportation Officials(AASHTO) have been uesd for the civil structural designs in Korea. The calibration of resistance factor based on the reliability theory for the development of limit state design of shallow foundation requires a reliable estimate of ultimate bearing capacity. The plate bearing test result is commonly used in geotechnical engineering practice to predict the ultimate bearing capacity of shallow foundation. Many graphical methods are specified in the design standards to define the ultimate bearing capacity based on the load-settlement curve. However, the ultimate bearing capacity determined based on the load-settlement curve has a low level of reliability to obtain an uniform ultimate load depend on engineering judgement. In this study, a well fitting nonlinear regression model is proposed to estimate the ultimate bearing capacity of shallow foundation and the results are compared with those calculated using previous graphical method. Applicability of LRFD for shallow foundations on weathered soils in Gwang-ju and Jeollanam-do provinces was investigated and resistance factor for these cases was proposed. The quantitative analyses on the uncertainty and resistance bias for shallow foundation on weathered soils were performed by collecting the statistical data about domestic case studies for design and construction of shallow foundation. Reliability analyses of shallow foundations were performed using LEVELs Ⅱ (First order Design value Approach) and Ⅲ (Monte Carlo Simulation) methods.