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Armin W Stuedlein - One of the best experts on this subject based on the ideXlab platform.
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reliability based serviceability Limit State Design for immediate settlement of spread footings on clay
Soils and Foundations, 2015Co-Authors: Jonathan C Huffman, Andrew W Strahler, Armin W StuedleinAbstract:Abstract While many spread footings constructed on clayey soils are Designed using consolidation settlement analyses for the serviceability Limit State (SLS), immediate settlement, or undrained displacement, of the footing may also contribute a significant portion of the total and/or differential settlement. Owing to possible magnitudes in immediate settlement, and with regard to stress history, assessment of the contribution of immediate settlement comprises an essential task for the understanding of the performance of a foundation system. This study proposes a simple reliability-based Design (RBD) procedure for assessing the allowable immediate displacement of a spread footing supported on clay in consideration of a desired serviceability Limit State. A relationship between the traditional spread footing bearing capacity equation and slope tangent capacity is established, then incorporated into a bivariate normalized bearing pressure–displacement model to estimate the mobilized resistance associated with a given displacement. The model was calibrated using a high quality database of full-scale loading tests compiled from various sources. The loading test data was used to characterize the uncertainty associated with the model and incorporated into an appropriate reliability-based performance function. Monte Carlo simulations were then used to calibrate a resistance factor with consideration of the uncertainty in the bearing pressure–displacement model, bearing capacity, applied bearing pressure, allowable displacement, and footing width. An example is provided to illustrate the application of the proposed procedure to estimate the bearing pressure for an allowable immediate displacement of a footing at the targeted probability and serviceability Limit State.
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reliability based ultimate Limit State Design of spread footings on aggregate pier reinforced clay
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2014Co-Authors: Armin W Stuedlein, Jonathan C Huffman, Seth C ReddyAbstract:This paper summarises the evaluation of previously existing and recently developed bearing capacity estimation methods for spread footings resting on aggregate pier reinforced clay. A load test database of full-scale footings resting on stone columns was used to generate an accurate ultimate Limit State Design model for bearing capacity and characterise the associated model uncertainty. Different levels of variability in area replacement ratio, slenderness ratio, length of pier, depth of footing embedment, and undrained shear strength, were incorporated in the resistance factor calibration in order to account for possible uncertainty in the load test database and future construction. Resistance factors were calibrated as a function of the ratio of dead to live load, reliability index, and total variability in the nominal bearing capacity. The operational factor of safety was computed for comparison to allowable stress Design procedures and indicated that typical factors of safety associated with current p...
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reliability based serviceability Limit State Design of spread footings on aggregate pier reinforced clay
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Jonathan C Huffman, Armin W StuedleinAbstract:Despite the availability of numerous methods to predict the load-displacement response of aggregate pier reinforced clay, accurately modeling the nonlinear displacement response remains challenging. Moreover, the uncertainty in the bearing pressure-displacement prediction has not been satisfactorily estimated, preventing the generation of reliability-based Design (RBD) procedures. This study proposes a simple RBD procedure for assessing the allowable bearing pressure for aggregate pier reinforced clay in consideration of the desired serviceability Limit State. A recently established bearing-capacity model for aggregate pier reinforced clay and its uncertainty is incorporated into a bivariate bearing pressure-displacement model appropriate for a wide range in displacement and calibrated using a high-quality full-scale load-test database. Several copulas were then evaluated for goodness of fit to the measured dependence structure between the coefficients of the selected two-parameter bearing pressure-displacement model. Following the generation of an appropriate performance function, a combined load and resistance factor is calibrated in consideration of the uncertainty in the bearing pressure-displacement model, bearing capacity, applied bearing pressure, allowable displacement, and footing width using Monte Carlo simulations of the respective source distributions. An example is provided to illustrate the application of the proposed procedure to estimate the bearing pressure for an allowable displacement at the desired serviceability Limit probability.
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serviceability Limit State Design for uplift of helical anchors in clay
Geomechanics and Geoengineering, 2014Co-Authors: Armin W Stuedlein, Marco UzielliAbstract:Presently, no displacement-based Design methodology exists for helical anchors subjected to tensile or uplift loading. This study investigates the statistical and probabilistic aspects of the load-displacement uncertainty associated with a database of thirty-seven uplift loading tests of helical anchors founded within cohesive soils. Initially, an ultimate resistance model is identified, and the semi-empirical uplift breakout factor statistically characterized. A relationship between ultimate resistance and slope tangent capacity is established, and used to form the basis for normalizing the load-displacement response. Hyperbolic and power law models are statistically evaluated for use in serving as a reference load-displacement model; the hyperbolic curve was selected based on goodness-of-fit statistics. Monte Carlo reliability simulations are used to establish an equivalent-deterministic load factor that associates the selected load factor with a probability of exceeding a pre-determined allowable uplif...
Bruce R. Ellingwood - One of the best experts on this subject based on the ideXlab platform.
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Reliability-Based Load Requirements for Formwork Shores during Concrete Placement
Journal of Structural Engineering-asce, 2015Co-Authors: James Reynolds, Kim J.r. Rasmussen, Bruce R. EllingwoodAbstract:AbstractOne challenge in assessing the safety of concrete formwork supporting structures is the difficulty in predicting the loads on shores. Very Limited studies on shore loads are available in the literature. This paper presents the results of a shore load investigation undertaken at three construction sites in Sydney. The study is focused on the vertical loads on shores during and following concrete placement. The statistical characteristics of the dead load effect and live load effect are determined. Structural reliability analyses are conducted to evaluate the reliability implications of the allowable stress Design and Limit State Design approaches for shoring structures. An optimal load combination is derived considering the probabilistic characteristics of shore loads.
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Limit State Design criteria for FRP strengthening of RC bridge components
Structural Safety, 2015Co-Authors: Naiyu Wang, Bruce R. EllingwoodAbstract:Fiber-reinforced polymer (FRP) composite materials provide novel, effective and potentially economical solutions for rehabilitating and strengthening existing reinforced and pre-stressed concrete bridges, buildings and other structures where deterioration has occurred or performance requirements have changed. FRP composites may be Designed to act as external flexural, shear or confinement reinforcement to increase the load capacity of the strengthened structural components. This paper summarizes research to develop technical support for practical Limit State (strength) Design criteria for repair and strengthening of reinforced and pre-stressed concrete bridge elements for compression and/or flexure using externally bonded FRP composite systems. The Limit State Design criteria take uncertainties in structural strength and stiffness into account using structural reliability methods, and will support and enhance the use of FRP materials in civil construction by providing engineers with rational guidelines for repair and strengthening.
Jonathan C Huffman - One of the best experts on this subject based on the ideXlab platform.
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reliability based serviceability Limit State Design for immediate settlement of spread footings on clay
Soils and Foundations, 2015Co-Authors: Jonathan C Huffman, Andrew W Strahler, Armin W StuedleinAbstract:Abstract While many spread footings constructed on clayey soils are Designed using consolidation settlement analyses for the serviceability Limit State (SLS), immediate settlement, or undrained displacement, of the footing may also contribute a significant portion of the total and/or differential settlement. Owing to possible magnitudes in immediate settlement, and with regard to stress history, assessment of the contribution of immediate settlement comprises an essential task for the understanding of the performance of a foundation system. This study proposes a simple reliability-based Design (RBD) procedure for assessing the allowable immediate displacement of a spread footing supported on clay in consideration of a desired serviceability Limit State. A relationship between the traditional spread footing bearing capacity equation and slope tangent capacity is established, then incorporated into a bivariate normalized bearing pressure–displacement model to estimate the mobilized resistance associated with a given displacement. The model was calibrated using a high quality database of full-scale loading tests compiled from various sources. The loading test data was used to characterize the uncertainty associated with the model and incorporated into an appropriate reliability-based performance function. Monte Carlo simulations were then used to calibrate a resistance factor with consideration of the uncertainty in the bearing pressure–displacement model, bearing capacity, applied bearing pressure, allowable displacement, and footing width. An example is provided to illustrate the application of the proposed procedure to estimate the bearing pressure for an allowable immediate displacement of a footing at the targeted probability and serviceability Limit State.
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reliability based ultimate Limit State Design of spread footings on aggregate pier reinforced clay
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2014Co-Authors: Armin W Stuedlein, Jonathan C Huffman, Seth C ReddyAbstract:This paper summarises the evaluation of previously existing and recently developed bearing capacity estimation methods for spread footings resting on aggregate pier reinforced clay. A load test database of full-scale footings resting on stone columns was used to generate an accurate ultimate Limit State Design model for bearing capacity and characterise the associated model uncertainty. Different levels of variability in area replacement ratio, slenderness ratio, length of pier, depth of footing embedment, and undrained shear strength, were incorporated in the resistance factor calibration in order to account for possible uncertainty in the load test database and future construction. Resistance factors were calibrated as a function of the ratio of dead to live load, reliability index, and total variability in the nominal bearing capacity. The operational factor of safety was computed for comparison to allowable stress Design procedures and indicated that typical factors of safety associated with current p...
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reliability based serviceability Limit State Design of spread footings on aggregate pier reinforced clay
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Jonathan C Huffman, Armin W StuedleinAbstract:Despite the availability of numerous methods to predict the load-displacement response of aggregate pier reinforced clay, accurately modeling the nonlinear displacement response remains challenging. Moreover, the uncertainty in the bearing pressure-displacement prediction has not been satisfactorily estimated, preventing the generation of reliability-based Design (RBD) procedures. This study proposes a simple RBD procedure for assessing the allowable bearing pressure for aggregate pier reinforced clay in consideration of the desired serviceability Limit State. A recently established bearing-capacity model for aggregate pier reinforced clay and its uncertainty is incorporated into a bivariate bearing pressure-displacement model appropriate for a wide range in displacement and calibrated using a high-quality full-scale load-test database. Several copulas were then evaluated for goodness of fit to the measured dependence structure between the coefficients of the selected two-parameter bearing pressure-displacement model. Following the generation of an appropriate performance function, a combined load and resistance factor is calibrated in consideration of the uncertainty in the bearing pressure-displacement model, bearing capacity, applied bearing pressure, allowable displacement, and footing width using Monte Carlo simulations of the respective source distributions. An example is provided to illustrate the application of the proposed procedure to estimate the bearing pressure for an allowable displacement at the desired serviceability Limit probability.
Kokkwang Phoon - One of the best experts on this subject based on the ideXlab platform.
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statistical analyses of model factors in reliability based Limit State Design of drilled shafts under axial loading
Journal of Geotechnical and Geoenvironmental Engineering, 2019Co-Authors: Chong Tang, Kokkwang Phoon, Yitjin ChenAbstract:AbstractThis study compiles 320 static-load tests to quantify the model factors in reliability-based Limit-State Design of drilled shafts under axial loading. At ultimate Limit-State, the model fac...
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characterization of model uncertainty in the static pile Design formula
Journal of Geotechnical and Geoenvironmental Engineering, 2011Co-Authors: Mahongo Dithinde, Kokkwang Phoon, Johan V. RetiefAbstract:Level 1 reliability methods have been internationally accepted as the basis for development of the new generation of geotechnical Design codes. A key requirement of this Design approach is the identification and quantification of uncertainties associated with the geotechnical Design under consideration. This paper presents four load test databases from South Africa for driven piles in noncohesive soils (29 tests), bored piles in noncohesive soils (33 tests), driven piles in cohesive soils (59 tests), and bored piles in cohesive soils (53 tests). The capacity model factor is defined as the ratio of the interpreted capacity (Chin-Davisson approach) and the predicted capacity (static pile Design formula). The uncertainty in the capacity model factor is modeled as a lognormal random variable. The model factor statistics reported in this study are required for reliability-based ultimate Limit State Design. The uncertainty in the load-settlement behavior is characterized by fitting measured load-settlement data to a hyperbolic equation and then normalizing the hyperbolic curve with the interpreted capacity. The resulting exercise reduces uncertainties in a set of nonlinear continuous curves to uncertainties in two hyperbolic curve-fitting parameters. This approach is practical and grounded realistically on the load test database with minimal assumptions. The hyperbolic parameter statistics reported in this study are required for reliability-based serviceability Limit State Design.
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why consider reliability analysis for geotechnical Limit State Design
Proceedings of the International Workshop, 2003Co-Authors: Kokkwang Phoon, D E Becker, Fred H Kulhawy, Yusuke Honjo, N K OvesenAbstract:There is a need to draw a clear distinction between accepting reliability analysis as a necessary theoretical basis for geotechnical Design and downstream calibration of simplified multiple- factor Design formats, with emphasis on the former. Reliability analysis provides a consistent method for propagation of uncertainties and a unifying framework for risk assessment across disciplines (structural and geotechnical Design) and national boundaries. Simplified reliability-based Design (RBD) equations are probably required for routine Design at present, but their Limitations have no bearing on the generality of reliability theory. If reliability analysis is accepted as the basis for developing multiple-factor formats, then it is necessary to define the characteristic values in an unambiguous way with reference to the probability distribution function. The key consideration is that the engineer should not be allowed to introduce additional conservatism into the Design by using some lower bound value, when the RBD equations are calibrated using, say, mean parameters. The implementation of reliability-based LRFD equations, along with potential advantages and pitfalls, is discussed using a specific example. If the goal of LRFD is to maintain uniform reliability, the example shows that a single resistance factor is not adequate. In practice, it is probably sufficient to partition the parameter space (spanning typical ranges of deterministic and statistical parameters) into smaller domains and calibrate a single resistance factor for each domain. Deviations from the target reliability index can be controlled to an acceptable level by adjusting the sizes of the domains.
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development of a reliability based Design framework for transmission line structure foundations
Journal of Geotechnical and Geoenvironmental Engineering, 2003Co-Authors: Kokkwang Phoon, Mircea GrigoriuAbstract:This paper presents the reliability-based Design (RBD) initiative sponsored by the Electric Power Research Institute for transmission line structure foundations. The role of RBD is presented within the context of geotechnical Limit State Design. Design parameters that are amenable to statistical description can be propagated systematically to a consistent measure of Design risk using reliability techniques such as the first-order reliability method (FORM). Less quantifiable factors are incorporated approximately into RBD by judicious selection of the target reliability level. A simplified RBD approach based on the load and resistance factor Design (LRFD) and multiple resistance factor Design (MRFD) formats is proposed for practical implementation. The resistance factors for the LRFD and MRFD formats are calibrated rigorously using FORM to produce Designs that can achieve a known level of reliability consistently.
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engineering judgment in the evolution from deterministic to reliability based foundation Design
Uncertainty in the Geologic Environment: from Theory to Practice, 1996Co-Authors: Fred H Kulhawy, Kokkwang PhoonAbstract:Engineering judgment has always played a predominant role in geotechnical Design and construction. Until earlier this century, most of this judgment was based on experience and precedents. The role of judgment in geotechnical practice has undergone significant changes since World War II as a result of theoretical, experimental, and field developments in soil mechanics, and more recently, in reliability theory. A clarification of this latter change particularly is needed to avoid misunderstanding and misuse of the new reliability-based Design (RBD) codes. This paper first provides a historical perspective of the traditional factor of safety approach. The fundamental importance of Limit State Design to RBD then is emphasized. Finally, an overview of RBD is presented, and the proper application of this new Design approach is discussed, with an example given of the ultimate Limit State Design of drilled shafts under undrained uplift loading. Judgment issues from traditional approaches through RBD are interwoven where appropriate.
James Reynolds - One of the best experts on this subject based on the ideXlab platform.
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system reliability based Limit State Design of support scaffolding systems
Engineering Structures, 2020Co-Authors: Cao Wang, James Reynolds, Kim J.r. Rasmussen, Hao Zhang, Shen YanAbstract:Abstract The safety of scaffold systems during construction is vital to prevent failures with catastrophic consequences. Engineering practice in the scaffolding industry, however, does not have a rational structural reliability basis as that used for buildings and bridges. The implementation of Design clauses for scaffold systems in the current standards partially relies on judgement suffering from the lack of data. With this regard, a reliability-based Limit State Design approach is developed in this study, making full use of the advanced finite element (FE) method and the recently accumulated statistical data of scaffolding resistance and construction loads. A stochastic finite element method is used to obtain the probabilistic characteristics of the ultimate load-carrying capacities of typical scaffolding frames, accounting for the uncertainties associated with structural geometry, material and stiffness properties. The latest construction load survey data is utilized. System reliability assessment is then performed to develop new Design criteria which are consistent with generally accepted structural reliability targets.
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Reliability-Based Load Requirements for Formwork Shores during Concrete Placement
Journal of Structural Engineering-asce, 2015Co-Authors: James Reynolds, Kim J.r. Rasmussen, Bruce R. EllingwoodAbstract:AbstractOne challenge in assessing the safety of concrete formwork supporting structures is the difficulty in predicting the loads on shores. Very Limited studies on shore loads are available in the literature. This paper presents the results of a shore load investigation undertaken at three construction sites in Sydney. The study is focused on the vertical loads on shores during and following concrete placement. The statistical characteristics of the dead load effect and live load effect are determined. Structural reliability analyses are conducted to evaluate the reliability implications of the allowable stress Design and Limit State Design approaches for shoring structures. An optimal load combination is derived considering the probabilistic characteristics of shore loads.