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The paper describes load and resistance factor design (LRFD) calibration for the resistance factor used in the Stiffness Method internal stability soil failure limit state for geogrid mechanically stabilized earth (MSE) walls. The Stiffness Method was recently adopted in the current American Association of State Highway and Transportation Officials LRFD Bridge Design Specifications in the US, and will appear in the next edition of the Canadian Highway Bridge Design Code. The paper describes the details of the calibration of the soil failure limit state which is unique to the Stiffness Method. Calibration outcomes include consideration of the concept of level of understanding in the selection of nominal load and resistance values which is unique to LRFD foundation engineering practice in Canada. A practical conclusion from these calculations is that if product line-specific creep test data are available to estimate the reinforcement secant creep stiffness used for design, then a resistance factor of 1.0 is reasonable for US practice. If only minimum average roll value tensile strength data are available, then a value of 0.95 is recommended for US practice. For Canadian practice, the corresponding values for typical level of understanding are 0.90 and 0.85, respectively. [ABSTRACT FROM AUTHOR]

The next edition of the Canadian Highway Bridge Design Code will contain a table of geotechnical resistance factors to be used for seismic design. This paper will estimate the geotechnical resistance factors for shallow foundations required to achieve various target maximum acceptable failure probabilities, which in turn may depend on the assumed design earthquake return period. The investigation will include consideration of design lifetime, uncertainty in the magnitude of the maximum lifetime earthquake event, and the uncertainty in ground properties. The results suggest resistance factors that are lower than commonly used at the moment in Canada and that the failure probability is not greatly dependent on the return period of the design earthquake. The paper will present recommendations on geotechnical resistance factors for seismic design that can be used to guide and calibrate future editions of civil design codes in Canada. [ABSTRACT FROM AUTHOR]

To account for uncertainties of load and resistance in a more rational way, reliability-based design (RBD) concepts have been increasingly applied to design bridge foundations. One of critical elements in the geotechnical RBD process is the characterization of model uncertainties. This paper compiles 126 and 23 reliable static load tests for steel H-piles in axial compression from two databases: Pile-Load Tests (PILOT) and Deep Foundation Load Test Database (DFLTD), respectively. The Davisson offset limit is adopted to define the measured resistance in clay, sand, and layered soil, which is verified with the L1–L2 method developed for drilled shafts. A hyperbolic model with two parameters is chosen to fit the measured load–settlement curves. The uncertainties in resistance calculations and the load–settlement curves are captured by a ratio (or model factor) of measured to calculated resistance and the hyperbolic parameters. The mean values, coefficients of variation, and the probability distributions of the model factors are established from 149 load tests. The statistics of the resistance model factor are applied to calibrate the resistance factors (for the ultimate limit state) in load and resistance factor design of steel H-piles in axial compression. In future, the statistics of the hyperbolic parameters can be incorporated into the development of RBD of steel H-piles at the serviceability limit state. [ABSTRACT FROM AUTHOR]

Canada has two national civil codes of practice that include geotechnical design provisions: the National Building Code of Canada and the Canadian Highway Bridge Design Code. For structural designs, both of these codes have been employing a load and resistance factor format embedded within a limit states design framework since the mid-1970s. Unfortunately, limit states design in geotechnical engineering has been lagging well behind that in structural engineering for the simple fact that the ground is by far the most variable (and hence uncertain) of engineering materials. Although the first implementation of a geotechnical limit states design code appeared in Denmark in 1956, it was not until 1979 that the concept began to appear in Canadian design codes, i.e., in the Ontario Highway Bridge Design Code, which later became the Canadian Highway Bridge Design Code (CHBDC). The geotechnical design provisions in the CHBDC have evolved significantly since their inception in 1979. This paper describes the latest advances appearing in the CHBDC along with the steps taken to calibrate its recent geotechnical resistance and consequence factors. [ABSTRACT FROM AUTHOR]