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.

Theoretical and Experimental Study on the Ultimate Strength of Corrugated Bulkheads

1997 ◽  
Vol 41 (04) ◽  
pp. 301-317
Author(s):  
Jeom K. Paik ◽  
Anil K. Thayamballi ◽  
Min S. Chun
Keyword(s):  
Ultimate Strength ◽  
Lateral Pressure ◽  
Limit State ◽  
Plate Thickness ◽  
Experimental Information ◽  
Design Guidelines ◽  
Design Parameters ◽  
Collapse Mechanism ◽  
Ultimate Limit State ◽  
Analytical Formulation

The objectives of the present study are to obtain experimental data on collapse strength of steel corrugated bulkhead models and also to develop a simple analytical formulation for ultimate strength useful in the design of corrugated bulkheads under static lateral pressure. Collapse tests on nine mild steel corrugated bulkhead models having five bays of corrugations are carried out, varying the corrugation angle, the plate thickness and the type of loading (axial compression and/or lateral pressure). Using the test data, the characteristics of the collapse mechanism for corrugated bulkheads are investigated. For purposes of rapid first cut estimates of strength, a new and simple analytical formulation for predicting the ultimate strength of corrugated bulkheads under hydrostatic pressure is derived based on an assumed stress distribution over the corrugation cross section at the ultimate limit state. The modeling error associated with the new formulation is established by comparing its predictions with the experimental results. The development of ultimate strength based design guidelines and the effect of design parameters such as the corrugation angle on ultimate strength of a corrugated bulkhead are then discussed. All experimental information and strength data are tabulated, which is a benefit in itself.

Joint Description Methods of Wind and Waves for the Design of Offshore Wind Turbines

2009 ◽  
Vol 43 (3) ◽  
pp. 23-33 ◽  
Author(s):  
Kim E. Mittendorf
Keyword(s):  
Wind Energy ◽  
Wind Wave ◽  
Limit State ◽  
Wave Model ◽  
Design Guidelines ◽  
Offshore Wind ◽  
Ultimate Limit State ◽  
Wave Loads ◽  
Offshore Wind Energy ◽  
The North

AbstractWind and wave loads are equally important for the design of offshore wind energy structures. For the design against an ultimate limit state or fatigue, the engineer has to estimate the combination of loads that are likely to occur simultaneously during the design life of the wind turbine. This is quite a complex task, involving different wind/wave models, load-calculation methods and statistical analysis of simultaneous extreme wind and wave conditions. Moreover, reliable and realistic methods for the assessment of the service life of an offshore wind energy converter under combined wind and wave loads are necessary. However, the current design guidelines (Det Norske Veritas or German Lloyd) provide hardly any information on how to model the wind and wave correlation. In this article, several approaches for obtaining the required wind-wave correlation for the design have been investigated. Manual wave forecasting methods, spectral sea state descriptions and numerical wave model data have been compared to simultaneously measured wind and wave data from the FINO research platform in the German Bight of the North Sea. The used approaches are general and can be easily applied to different data sets from different regions.

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.

scholarly journals Statistics of model factors in reliability-based design of axially loaded driven piles in sand

2018 ◽  
Vol 55 (11) ◽  
pp. 1592-1610 ◽  
Author(s):  
Chong Tang ◽  
Kok-Kwang Phoon
Keyword(s):  
Probability Distributions ◽  
Limit State ◽  
Hyperbolic Model ◽  
Driven Piles ◽  
Copula Theory ◽  
Resistance Factors ◽  
Reliability Based Design ◽  
Measured Resistance ◽  
Axially Loaded ◽  
Two Parameters

This paper compiles 162 reliable field load tests for axially loaded driven piles in sand from previous studies. The L1–L2 method is adopted to interpret the measured resistance from the load–settlement data. The accuracy of resistance calculations with the ICP-05 and UWA-05 methods based on cone penetration test profile is evaluated by the ratio (bias or model factor) of the measured resistance to the calculated resistance. A hyperbolic model with two parameters, where the load component is normalized by the measured resistance, is utilized to fit the measured load–settlement curves. The means, coefficients of variation, and probability distributions for the resistance model factor and the hyperbolic parameters are established from the database. Copula theory is employed to characterize the correlation structure within the hyperbolic parameters. The statistical properties of the model factors are applied to calibrate the resistance factors in simplified reliability-based designs of closed-end piles driven into sand at the ultimate and serviceability limit state by Monte-Carlo simulations. A simple example is provided to illustrate the application of the proposed resistance factors to estimate the allowable load for an allowable settlement at the desired serviceability limit probability.

Reliability Analyses of Suction Caissons for FPSO Systems

2008 ◽  
Author(s):  
Celestino Valle-Molina ◽  
Ernesto Heredia-Zavoni ◽  
Francisco L. Silva-Gonza´lez
Keyword(s):  
Limit Equilibrium ◽  
Limit State ◽  
Ultimate Limit State ◽  
Suction Caisson ◽  
Capacity Model ◽  
Probabilistic Characterization ◽  
Partial Safety Factors ◽  
Ultimate Limit ◽  
Suction Caissons

The reliability formulation for the analyses of suction caissons subjected to environmental loadings from FPSO systems is presented in this paper. The capacity model for the suction caisson assumes normally consolidated clays with a linear variation on the undrained shear strength. The limit equilibrium method was used to assess the inclined capacity of suction caissons. The probabilistic characterization of the environmental loading is associated to deep water sites in the Bay of Campeche in the Gulf of Mexico. The reliability of the suction caissons was performed by means of Monte Carlo simulations and calibration of partial safety factors was carried out for the ultimate limit state using the design equation proposed by DNV [1].

Bearing Capacity of a Skirted Foundation Under VMH Loading

2003 ◽  
Author(s):  
Susan Gourvenec ◽  
Mark Randolph
Keyword(s):  
Finite Element ◽  
Design Method ◽  
Load Capacity ◽  
Limit State ◽  
Design Guidelines ◽  
Shallow Foundation ◽  
Combined Loading ◽  
Ultimate Limit State ◽  
Finite Element Analyses ◽  
Offshore Industry

This paper presents results from a series of three-dimensional finite element analyses investigating the ultimate limit state of a circular skirted shallow foundation over a comprehensive range of combined vertical, moment and horizontal loading. Failure loci in V:M:H load space derived from the finite element analyses are compared with limit state predictions from the offshore industry design guidelines [1]. The comparison highlights considerable conservatism of the current design method largely due to poor representation of the response to fully combined loading and neglect of the tensile capacity achieved with foundation skirts. These shortcomings are particularly significant with respect to foundations for offshore conditions and result in an oversight of considerable potential load capacity in design.

Reliability Based Design Criteria for Installation of Pipelines in the Bay of Campeche, Mexico: Part 1

2002 ◽  
Author(s):  
Robert Bea ◽  
Tao Xu ◽  
Ernesto Heredia-Zavoni ◽  
Leonel Lara ◽  
Rommel Burbano
Keyword(s):  
Limit State ◽  
Companion Paper ◽  
Design Guidelines ◽  
Design Criteria ◽  
Ultimate Limit State ◽  
Reliability Based Design ◽  
Factor Design ◽  
Load And Resistance Factor ◽  
Ultimate Limit ◽  
Allowable Stress Design

Studies have been performed to propose reliability based design criteria for the installation of pipelines in the Bay of Campeche, Mexico. This paper summarizes the reliability formulations that were used to develop Allowable Stress Design and Load and Resistance Factor Design guidelines for Ultimate Limit State conditions, background on the target reliabilities that were used in the development, and the methods that were used to characterize the demands (loads, displacements) induced in pipelines during their installation. This paper summarizes data that was gathered during the installation of pipelines in the Bay of Campeche to help define the Biases (actual stresses/calculated stresses) associated with the analytical model used to predict installation demands. These results are compared with those published previously based on other field and laboratory tests. A companion paper details the analyses of pipeline Ultimate Limit State capacities and the Biases associated with these capacities.

Load and resistance factor design of shallow foundations against bearing failure

2008 ◽  
Vol 45 (11) ◽  
pp. 1556-1571 ◽  
Author(s):  
Gordon A. Fenton ◽  
D. V. Griffiths ◽  
Xianyue Zhang
Keyword(s):  
Bearing Capacity ◽  
Limit State ◽  
Resistance Factor ◽  
Shallow Foundation ◽  
Ultimate Limit State ◽  
Full Potential ◽  
Design Codes ◽  
Reliability Based Design ◽  
Factor Design ◽  
Load And Resistance Factor

Shallow foundation designs are typically governed either by settlement, a serviceability limit state, or by bearing capacity, an ultimate limit state. While geotechnical engineers have been designing against these limit states for over half a century, it is only recently that they have begun to migrate towards reliability-based designs. At the moment, reliability-based design codes are generally derived through calibration with traditional working stress designs. To take advantage of the full potential of reliability-based design the profession must go beyond calibration and take geotechnical uncertainties into account in a rational fashion. This paper proposes a load and resistance factor design (LRFD) approach for the bearing capacity design of a strip footing, using load factors as specified by structural codes. The resistance factors required to achieve an acceptable failure probability are estimated as a function of the spatial variability of the soil and by the level of “understanding” of the soil properties in the vicinity of the foundation. The analytical results, validated by simulation, are primarily intended to aid in the development of the next generation of reliability-based geotechnical design codes, but can also be used to assess the reliability of current designs.

On the Behavior and Design of Stiffened Plates in Ultimate Limit State

1978 ◽  
Vol 22 (04) ◽  
pp. 238-244
Author(s):  
T. H. Soreide ◽  
T. Moan ◽  
N.T. Nordsve
Keyword(s):  
Finite Element ◽  
Limit State ◽  
Axial Loading ◽  
Stiffened Plates ◽  
Ultimate Limit State ◽  
Element Formulation ◽  
Finite Element Program ◽  
Global Buckling ◽  
Element Program ◽  
Ultimate Limit

The behavior and design of stiffened plates in the ultimate limit state are studied. A finite element formulation for panel behavior considering general loading conditions, material properties, geometry, boundary conditions, and initial deflections is presented. Some results obtained by a finite element program are displayed and discussed. The problems considered comprise perfect and initially deflected plate-strips subjected to lateral pressure, single-span and two-span beam-columns under axial loading, and failure of a stiffened plate designed for simultaneous local and global buckling. Finally, design criteria are briefly discussed and recommendations for future work are given.

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