Load And Resistance Factor Design Lrfd For Deep Foundations And The Challenges With Implementation Into Design Performance PDF Download

With the implementation of load and resistance factor design (LRFD) by the U.S. Federal Highway Administration, the design of deep foundations is migrating from Level I (e.g., allowable stress design) codes to Level II codes (e.g., LRFD). Nevertheless, there are still unsolved issues regarding the implementation of load and resistance factor design. For example, there is no generally accepted guidance on the statistical characterization of soil properties. Moreover, the serviceability limit check in LRFD is still deterministic. No uncertainties arising in soil properties, loads and design criteria are taken into account in the implementation of LRFD. In current practice, the load factors and resistances are taken as unity, and deterministic models are applied to evaluate the displacements of geotechnical structures. In order to address the aforementioned issues of LRFD, there is a need for a computational method for conducting reliability analysis and computational tools for statistically characterizing the variability of soil properties. The objectives of this research are: 1) to develop a mathematically sound computational tool for conducting reliability analysis for deep foundations; and 2) to develop the associated computational method that can be used to determine the variability model of a soil property. To achieve consistency between the strength limit check and the serviceability limit check of the LRFD framework, performance-based design methodology is developed for deep foundation design. In the proposed methodology, the design criteria are defined in terms of the displacements of the structure that are induced by external loads. If the displacements are within the specified design criteria, the design is considered satisfactory. Otherwise, failure is said to occur. In order to calculate the probability of failure, Monte Carlo simulation is employed. In Monte Carlo simulation, the variability of the random variables that are involved in the reliability analysis is captured by simulating a large number of samples according to their respective probability distributions. Next, the simulations of the random variables are used as the input to the commonly used p-y method and load transfer method to evaluate the load-displacement behavior. Once the displacements are calculated, it can be determined whether or not failure will occur. Accordingly, the failure probability is calculated as the number of failure events to the total number of simulations. A series of computer programs have been developed and validated based on the proposed performance-based design methodology. These computer programs can be used to conduct reliability analysis for designing a drilled shaft. To determine the variability model of soil properties that will be used as input to the computer programs, a computational method has been developed in which the blow counts in a standard penetration test are required as inputs. It is found that the consideration of the dependence structure of soil properties is important for reliability analysis.