Probabilistic analysis of drilled shaft service limit state using the "t–z" method

2006 ◽  
Vol 43 (12) ◽  
pp. 1324-1332 ◽  
Author(s):  
Anil Misra ◽  
Lance A Roberts
Keyword(s):  
Limit State ◽  
Drilled Shafts ◽  
Cumulative Distribution ◽  
Hyperbolic Model ◽  
Drilled Shaft ◽  
Large Set ◽  
Reliability Based Design ◽  
Service Limit State ◽  
Load Displacement ◽  
Load And Resistance Factor

The utility of the load and resistance factor design (LRFD) approach is being increasingly recognized for the design of drilled shafts. The current LRFD methodologies of drilled shaft design would be more efficient if reliability based design approaches were used for service limit state design. In this paper, the "t–z" methodology is utilized to develop probabilistic approaches for axial service limit state analysis of drilled shafts. Two different models of the soil–shaft interaction are implemented for load displacement calculations: (1) an ideal elastoplastic model, and (2) a hyperbolic model. For both of these soil–shaft interactions, Monte Carlo simulation is used to obtain a large set of load–displacement curves assuming lognormal distributions for the shaft–soil interface properties. The load–displacement curves are analyzed to develop two alternate methods for determining the probability of drilled shaft failure at the service limit state. As a result, cumulative distribution histograms are developed for drilled shaft load capacities at allowable head displacements. These results may be utilized to obtain resistance factors that can be applied to LRFD based service limit state design.Key words: drilled shaft, serviceability, failure probability, load displacement relation, "t–z" method.

scholarly journals Load and resistance factor design of drilled shafts subjected to lateral loading at service limit state

2018 ◽  
Author(s):  
◽  
Minh Dinh Uong
Keyword(s):  
Limit State ◽  
Design Procedure ◽  
Drilled Shafts ◽  
Resistance Factor ◽  
Lateral Loading ◽  
Drilled Shaft ◽  
Resistance Factors ◽  
Service Limit State ◽  
Load And Resistance Factor ◽  
Aashto Lrfd

Since 2007, the American Association of State Highway Administration Officials (AASHTO) has made utilization of Load and Resistance Factor Design (LRFD) mandatory on all federally-funded new bridge projects (AASHTO, 2007). However, currently, there are no guidelines implementing LRFD techniques for design of drilled shaft subjected to lateral loads using reliability-based analysis. On a national level, the AASHTO LRFD Bridge Design Specifications (AASHTO, 2012) specify that a resistance factor of 1.0 be used for design of drilled shafts subjected to lateral loading at service limit state, which means reliability-based analyses for calibration of resistance factors have not been performed. Therefore, there is a need to create a LRFD procedure for drilled shafts subjected to lateral loading at service limit state that has reliability-based calibrated resistance factors applicable for future projects. The research focuses on the reliability-based analysis of drilled shaft subjected to lateral loading, characterize lateral load transfer model of drilled shafts in shale, probabilistic calibrate resistance factor and contribute to the development of design procedure using LRFD. The objective of this work is to improve the design of drilled shaft subjected to lateral loading using LRFD at service limit state by providing a more reliable design procedure than the current AASHTO LRFD procedure for drilled shafts subjected to lateral loading at service limit state.

scholarly journals Serviceability limit state reliability-based design of augered cast-in-place piles in granular soils

2017 ◽  
Vol 54 (12) ◽  
pp. 1704-1715 ◽  
Author(s):  
Seth C. Reddy ◽  
Armin W. Stuedlein
Keyword(s):  
Lower Bound ◽  
Limit State ◽  
Companion Paper ◽  
Resistance Factor ◽  
Granular Soils ◽  
Serviceability Limit State ◽  
Reliability Based Design ◽  
Wide Range ◽  
Load Displacement ◽  
Load And Resistance Factor

This study proposes a reliability-based design procedure to evaluate the allowable load for augered cast-in-place (ACIP) piles installed in predominately granular soils based on a prescribed level of reliability at the serviceability limit state. The ultimate limit state (ULS) ACIP pile–specific design model proposed in the companion paper is incorporated into a bivariate hyperbolic load–displacement model capable of describing the variability in the load–displacement relationship for a wide range of pile displacements. Following the approach outlined in the companion paper, distributions with truncated lower-bound capacities are incorporated into the reliability analyses. A lumped load-and-resistance factor is calibrated using a suitable performance function and Monte Carlo simulations. The average and conservative 95% lower-bound prediction intervals for the calibrated load-and-resistance factor resulting from the simulations are provided. Although unaccounted for in past studies, the slenderness ratio is shown to have significant influence on foundation reliability. Because of the low uncertainty in the proposed ULS pile capacity prediction model, the use of a truncated distribution has moderate influence on foundation reliability.

Practical Reliability-Based Design Approach for Foundation Engineering

1996 ◽  
Vol 1546 (1) ◽  
pp. 94-99 ◽  
Author(s):  
Kok Kwang Phoon ◽  
Fred H. Kulhawy
Keyword(s):  
Research Study ◽  
Limit State ◽  
Drilled Shafts ◽  
Ultimate Limit State ◽  
Foundation Engineering ◽  
Reliability Level ◽  
Reliability Based Design ◽  
Ultimate Limit State Design ◽  
Ultimate Limit ◽  
Selection Of

A research study was completed recently that was directed toward the development of practical, reliability-based design (RBD) equations specifically for foundation engineering. Some of the key RBD principles used in the study are presented. The important considerations involved in the development of practical and robust RBD criteria are emphasized. In particular, the selection of an appropriate reliability assessment technique and the careful characterization and compilation of geotechnical variabilities are important because of their central role in the calculation of the probability of failure and the assessment of the target reliability level. An overview of a simplified RBD approach is given, and an application of this approach to the ultimate limit state design of drilled shafts under undrained uplift loading is discussed.

Dependability-Based Design Optimization of Degrading Engineering Systems

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Gordon J. Savage ◽  
Young Kap Son
Keyword(s):  
Design Optimization ◽  
Lifetime Cost ◽  
Limit State ◽  
Value Theory ◽  
Cumulative Distribution ◽  
Reliability Based Design ◽  
Design Variables ◽  
Reliability Method ◽  
Distribution Parameters ◽  
Present Worth

In this paper, we present a methodology that helps select the distribution parameters in degrading multiresponse systems to improve dependability at the lowest lifetime cost. The dependability measures include both quality (soft failures) and reliability (hard failures). Associated costs of scrap, rework, and warrantee work are included. The key to the approach is the fast and efficient creation of the system cumulative distribution function through a series of time-variant limit-state functions. Probabilities are evaluated by Monte Carlo simulation although the first-order reliability method is a viable alternative. The cost objective function that is common in reliability-based design optimization is expanded to include a lifetime loss of performance cost, herein based on present worth theory (also called present value theory). An optimum design in terms of distribution parameters of the design variables is found via a methodology that involves minimizing cost under performance policy constraints over the lifetime as the system degrades. A case study of an over-run clutch provides the insights and potential of the proposed methodology.

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