Evaluation of model uncertainties in reliability-based design of steel H-piles in axial compression

2018 ◽  
Vol 55 (11) ◽  
pp. 1513-1532 ◽  
Author(s):  
Chong Tang ◽  
Kok-Kwang Phoon
Keyword(s):  
Axial Compression ◽  
Limit State ◽  
Load Test ◽  
Hyperbolic Model ◽  
Ultimate Limit State ◽  
Model Uncertainties ◽  
Deep Foundation ◽  
Mean Values ◽  
Reliability Based Design ◽  
Load Tests

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.

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.

Statistical evaluation of model factors in reliability calibration of high-displacement helical piles under axial loading

2020 ◽  
Vol 57 (2) ◽  
pp. 246-262 ◽  
Author(s):  
Chong Tang ◽  
Kok-Kwang Phoon
Keyword(s):  
Limit State ◽  
Axial Loading ◽  
Design Guidelines ◽  
Resistance Factor ◽  
Hyperbolic Model ◽  
Ultimate Limit State ◽  
Dense Sand ◽  
Capacity Model ◽  
Helical Piles ◽  
Two Parameters

An industry survey suggests an increasing application of high-displacement helical piles with greater shaft and helix diameters to support various structures. In this paper, a database of 84 static load tests is compiled and analyzed to evaluate the disturbance effect and characterize the model factors that can be used for reliability-based limit state design. The measured capacity is defined as the load at a pile head settlement equal to 5% of helix diameter. For similar helix configurations tested at the same site, the ratio of uplift to compression capacity indicates a low degree of disturbance for very stiff clay (0.8–1) and a medium degree of disturbance for dense sand (0.6–0.8). At the ultimate limit state, the model factor is defined as the ratio between measured and calculated capacity, where three design guidelines are considered. A hyperbolic model with two parameters is used to fit the load–displacement curves. At the serviceability limit state, the model factor can be defined with the hyperbolic parameters. Based on the database, probabilistic distributions of the capacity model factor and hyperbolic parameters are established. Finally, the capacity model statistics are applied to calculate the resistance factor in the load and resistance factor design.

Fatigue and Ultimate Limit State of Grouted Tubular Joints

2002 ◽  
Author(s):  
Darren J. Morahan ◽  
Minaz Lalani
Keyword(s):  
Large Scale ◽  
Limit State ◽  
Cost Effective ◽  
Ultimate Limit State ◽  
Tubular Joints ◽  
Detail Design ◽  
Double Skin ◽  
Load Tests ◽  
Two Phases ◽  
Ultimate Limit

A joint industry project commenced in 1993 to develop a design manual for tubular joints, which are strengthened or repaired through chord grout filling. This project was carried out in two phases and was completed in the late 1990’s. The project comprised the conduct of over 200 SCF and ultimate load tests on large scale as-welded and grouted tubular joints. In addition to the testing programme, studies on offshore deployment were carried out to ensure that complete chord grout filling was achievable for all practical scenarios. The primary reason for carrying out this project is the industry-wide recognition that chord grout filling represents an extremely cost-effective and mechanically efficient method to strengthen or repair tubular joints. Further, it has been recognised that double-skin joints (e.g. pile through leg with annulus grout-filled) are often present in structures and the enhanced strength and fatigue characteristics as a result could be exploited to permit more efficient new platform designs or better estimation of joint performance for existing installations. Although API RP2A [1] and ISO [2] recommendations permit the use of grouted joints, little guidance is provided. The guidance that is provided is based on public domain data and engineering principles. This project was carried out to generate a substantial amount of new data/information, leading to the creation of a detail design manual for grouted joints [3,4].

scholarly journals Reliability-Based Ultimate Limit State Design of Micropiles in Ontario Soils

2021 ◽  
Author(s):  
Alexandre P. R. P. Almeida
Keyword(s):  
Bond Strength ◽  
Failure Load ◽  
Limit State ◽  
Accurate Estimation ◽  
Ultimate Limit State ◽  
Resistance Factors ◽  
Ground Conditions ◽  
Load Tests ◽  
Ultimate Limit State Design ◽  
Ultimate Limit

The design practice of micropiles in Ontario soils under the ultimate limit state was improved through both statistical and reliability analyses of a database of 40 micropile load tests. Micropile design is extremely dependent on engineering experience and judgement due to the lack of an accurate estimation of the bond strength. The FHWA manual of micropiles only provides wide ranges of bond strength in different ground conditions. Micropile load tests were conducted by Keller Foundations Ltd and collected for this study. From a statistical analysis, Fuller and Hoy’s method was selected as the best method to estimate the failure load from non-failed tests. Adjusted parameters were given to predict the bond strength of micropiles. A method was proposed to estimate the contributions from the cased length and the tip to the total resistance. In the end, a reliability analysis was conducted and the resistance factors were recalibrated.

scholarly journals Reliability-Based Ultimate Limit State Design of Micropiles in Ontario Soils

2021 ◽  
Author(s):  
Alexandre P. R. P. Almeida
Keyword(s):  
Bond Strength ◽  
Failure Load ◽  
Limit State ◽  
Accurate Estimation ◽  
Ultimate Limit State ◽  
Resistance Factors ◽  
Ground Conditions ◽  
Load Tests ◽  
Ultimate Limit State Design ◽  
Ultimate Limit

The design practice of micropiles in Ontario soils under the ultimate limit state was improved through both statistical and reliability analyses of a database of 40 micropile load tests. Micropile design is extremely dependent on engineering experience and judgement due to the lack of an accurate estimation of the bond strength. The FHWA manual of micropiles only provides wide ranges of bond strength in different ground conditions. Micropile load tests were conducted by Keller Foundations Ltd and collected for this study. From a statistical analysis, Fuller and Hoy’s method was selected as the best method to estimate the failure load from non-failed tests. Adjusted parameters were given to predict the bond strength of micropiles. A method was proposed to estimate the contributions from the cased length and the tip to the total resistance. In the end, a reliability analysis was conducted and the resistance factors were recalibrated.

Evaluation of peak side resistance for rock socketed shafts in weak sedimentary rock from an extensive database of published field load tests: a limit state approach

2019 ◽  
Vol 56 (12) ◽  
pp. 1816-1831 ◽  
Author(s):  
Pouyan Asem ◽  
Paolo Gardoni
Keyword(s):  
Test Data ◽  
Limit State ◽  
Deformation Modulus ◽  
Load Test ◽  
Resistance Factors ◽  
Strength Limit ◽  
Side Resistance ◽  
Load Tests ◽  
Load And Resistance Factor

This paper presents analyses of the measured peak side resistance of rock sockets constructed in weak claystone, shale, limestone, siltstone, and sandstone. The peak side resistance is obtained from in situ axial load tests on drilled shafts, anchors, and plugs. The parameters that affect the development of peak side resistance are determined using in situ load test data. It is found that peak side resistance increases with the unconfined compressive strength and deformation modulus of the weak rock, and decreases with the increase in length of the shear surface along the rock socket sidewalls. The increase in socket diameter also slightly decreases the peak side resistance. Additionally, it is found that the initial normal stresses do not significantly affect the measured peak side resistance in the in situ load tests. The in situ load test data are used to develop an empirical design equation for determination of the peak side resistance. The proposed model for peak side resistance and the reliability analysis are used to determine the corresponding resistance factors for use in the load and resistance factor design framework for assessment of the strength limit state.

Performance of helical piles in oil sand

2009 ◽  
Vol 46 (9) ◽  
pp. 1046-1061 ◽  
Author(s):  
Mohammed Sakr
Keyword(s):  
Full Scale ◽  
Load Test ◽  
Test Results ◽  
Lateral Loads ◽  
Oil Sand ◽  
Deep Foundation ◽  
Helical Piles ◽  
Load Tests ◽  
Pile Load Test ◽  
Pile Load Tests

The results of a comprehensive pile load-test program and observations from field monitoring of helical piles with either a single helix or double helixes installed in oil sand are presented in this paper. Eleven full-scale pile load tests were carried out including axial compression, uplift, and lateral load tests. The results of the full-scale load tests are used to develop a theoretical design model for helical piles installed in oil sand. Test results confirm that the helical pile is a viable deep foundation option for support of heavily loaded structures. The test results also demonstrated that circular-shaft helical piles can resist considerable lateral loads.

Consequence factors in the ultimate limit state design of shallow foundations

2011 ◽  
Vol 48 (2) ◽  
pp. 265-279 ◽  
Author(s):  
Gordon A. Fenton ◽  
D. V. Griffiths ◽  
Olaide O. Ojomo
Keyword(s):  
Limit State ◽  
Shallow Foundations ◽  
Resistance Factor ◽  
Shallow Foundation ◽  
Ultimate Limit State ◽  
Resistance Factors ◽  
Limit State Design ◽  
Reliability Based Design ◽  
Load And Resistance Factors ◽  
Load And Resistance Factor

The reliability-based design of shallow foundations is generally implemented via a load and resistance factor design methodology embedded in a limit state design framework. For any particular limit state, the design proceeds by ensuring that the factored resistance equals or exceeds the factored load effects. Load and resistance factors are determined to ensure that the resulting design is sufficiently safe. Load factors are typically prescribed in structural codes and take into account load uncertainty. Factors applied to resistance depend on both uncertainty in the resistance (accounted for by a resistance factor) and desired target reliability (accounted for by a newly introduced consequence factor). This paper concentrates on how the consequence factor can be defined and specified to adjust the target reliability of a shallow foundation designed to resist bearing capacity failure.

scholarly journals Ultimate limit state reliability-based design of augered cast-in-place piles considering lower-bound capacities

2017 ◽  
Vol 54 (12) ◽  
pp. 1693-1703 ◽  
Author(s):  
Seth C. Reddy ◽  
Armin W. Stuedlein
Keyword(s):  
Lower Bound ◽  
Limit State ◽  
Resistance Factor ◽  
Reasonable Assumption ◽  
Ultimate Limit State ◽  
Design Models ◽  
Resistance Factors ◽  
Reliability Based Design ◽  
The Impact ◽  
Ultimate Limit

The use of augered cast-in-place (ACIP) piles for transportation infrastructure requires an appropriate reliability-based design (RBD) procedure. In an effort to improve the accuracy of an existing design model and calibrate appropriate resistance factors, this study presents a significantly revised RBD methodology for estimating the shaft and toe bearing capacity of ACIP piles using a large database consisting of static loading tests in predominately granular soils. The proposed design models are unbiased, as opposed to those currently recommended. Based on the reasonable assumption that a finite lower-bound resistance limit exists, lower-bound design lines are developed for shaft and toe bearing resistance by applying a constant ratio to the proposed design models. Resistance factors are calibrated at the strength or ultimate limit state (ULS) for ACIP piles loaded in compression and tension for two commonly used target probabilities of failure with and without lower-bound limits. For piles loaded in compression, separate resistance factors are calibrated for the proposed shaft and toe bearing resistance models. The inclusion of a lower-bound limit for piles loaded in tension results in a 24%–50% increase in the calibrated resistance factor. For piles loaded in compression, the application of a lower-bound limit results in a 20%–150% increase in the calibrated resistance factor, and represents a significant increase in useable pile capacity. Although the impact of a lower-bound limit on resistance factor calibration is directly dependent on the degree of uncertainty in the distribution of resistance, this effect is outweighed by the type of distribution selected (i.e., normal, lognormal) at more stringent target probabilities of failure due to differences in distribution shape at the location of the lower-bound limit. A companion paper explores the use of the revised ULS model in a reliability-based serviceability limit state design framework.

Geotechnical resistance factors for ultimate limit state design of deep foundations in cohesive soils

2011 ◽  
Vol 48 (11) ◽  
pp. 1729-1741 ◽  
Author(s):  
Mehrangiz Naghibi ◽  
Gordon A. Fenton
Keyword(s):  
Limit State ◽  
Cohesive Soil ◽  
Ultimate Limit State ◽  
Deep Foundations ◽  
Cohesive Soils ◽  
Deep Foundation ◽  
Resistance Factors ◽  
Limit State Design ◽  
Ultimate Limit State Design ◽  
Ultimate Limit

This paper investigates the ultimate limit state load and resistance factor design (LRFD) of deep foundations founded within purely cohesive soils. The geotechnical resistance factors required to produce deep foundation designs having a maximum acceptable failure probability are estimated as a function of site understanding and failure consequence. The probability theory developed in this paper, used to determine the resistance factors, is verified by a two-dimensional random field Monte Carlo simulation of a spatially variable cohesive soil. The agreement between theory and simulation is found to be very good, and the theory is then used to derive the required geotechnical resistance factors. The results presented in this paper can be used to complement current ultimate limit state design code calibration efforts for deep foundations in cohesive soils.

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