Robustness of Constant Load and Resistance Factor Design Factors for Drilled Shafts in Multiple Strata

Ching, Jianye; Phoon, Kok‐Kwang; Chen, Jie‐Ru; Park, Jae Hyun

doi:10.1061/(asce)gt.1943-5606.0000849

Cited by 14 publications

(6 citation statements)

References 5 publications

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“…It is known that the constant load and resistance factors usually lead to designs with large variations of reliability; thus, they should be improved to achieve a robust design (Ching et al, 2013). For an RC column designed with 50 years of service life, the target reliability is usually 3.8 for both tension failure and compression failure in Eurocode.…”

Section: Improved Design Measures and Resultsmentioning

confidence: 99%

Reliability evaluation of reinforced concrete columns designed by Eurocode for wind-dominated combination considering random loads eccentricity

Jiang

Peng

Beer

et al. 2019

Advances in Structural Engineering

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With the capacity models in the 2004 edition of the European Committee for Standardization’s Standard Design of Concrete Structures, a more realistic limit state function is obtained for reinforced concrete columns with random loads eccentricity. Using this function, the applicability of the code-based design factors is discussed. Taking the wind-dominated combination as an example, the probabilistic distribution of loads eccentricity and the statistics of column resistance are analyzed for representative cases. The analysis indicates that the possible loads eccentricity is scattered over a large range, and the probabilistic model of column resistance varies from case to case, which is largely different from the resistance model assumed in previous reliability calibration. With Monte Carlo simulation, the column reliability and the contributions of both tension failure and compression failure to the total failure probability are calculated and obtained for different cases. The results show that the fixed loads eccentricity criterion underestimates differences in the reliability of columns for different loads eccentricity cases and overestimates the column reliability in some tension failure cases. Furthermore, it is found that the tension failure mode contributes most to the total failure probability for not only some columns designed to fail in tension failure but also for some columns designed to fail in compression failure. To attain a robust design, a group of optimum wind load factors varying with cases is recommended. The new calibration results prove that the recommended wind local factors can achieve a better goal.

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Section: Improved Design Measures and Resultsmentioning

confidence: 99%

Reliability evaluation of reinforced concrete columns designed by Eurocode for wind-dominated combination considering random loads eccentricity

Jiang

Peng

Beer

et al. 2019

Advances in Structural Engineering

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“…Constant resistance factors can effectively account for variability and uncertainty introduced by geotechnical analysis methods because the variability and uncertainty do not directly depend on the variability of a given site or the uncertainty in geotechnical design parameters. However, use of constant resistance factors practically precludes the potential to achieve consistent reliability because it restricts means to effectively account for differences in the variability and uncertainty of geotechnical design parameters across a broad range of sites and projects (10). Use of constant resistance factors also diminishes the apparent value of site characterization activities that might be used to reduce uncertainty in geotechnical design parameters because the resistance factor prescribed is independent of parameter uncertainty.…”

Section: Design Methods Consideredmentioning

confidence: 99%

Effect of Number of Soil Strength Measurements on Reliability of Spread Footing Designs

Loehr

Ding

Likos

2015

Transportation Research Record

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One of the primary objectives of using load and resistance factor design (LRFD) is to produce designs that consistently reach some established target reliability. Achieving this objective is challenging in geotechnical applications because variability and uncertainty in design input parameters vary substantially from site to site and with different quantities of site characterization. Analyses were performed to simulate spread footing design by using different numbers of undrained shear strength measurements. Results revealed that the likelihood was high of over- or underestimating both the mean value of a design parameter and the uncertainty in the mean value when small numbers of measurements were considered. The analyses also revealed that LRFD methods that prescribed constant resistance factors frequently produced underreliable designs when small numbers of measurements were considered. The percentage of underreliable designs decreased when increasing numbers of measurements were used. However, this decreasing percentage of underreliable designs was accompanied by an increasing percentage of overreliable designs rather than an increasing percentage of designs that achieved the target probability of failure within practical limits. In contrast, LRFD methods prescribing resistance factors that depended on uncertainty in design parameters tended to produce a consistently low percentage of underreliable designs when more than five measurements were used. As greater numbers of measurements were considered, such methods produced increasing percentages of designs that practically achieved the target probability of failure and decreasing percentages of overreliable designs.

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“…On the contrary, as noted by , a constant partial factor is unlikely to provide a uniform reliability level when the variability of the governing parameter is high. Ching et al (2013) and Phoon, Ching, and Chen (2013) pointed out this difficulty for foundation design in layered soils.…”

Section: Examples Of Characteristic Value Evaluationmentioning

confidence: 99%

What is a characteristic value for soils?

Länsivaara

Phoon

Ching

2021

Georisk: Assessment and Management of Risk for Engineered Syste

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The choice of the characteristic value of a material property is fundamental in all civil engineering design and critical in geotechnical engineering. Based on our tradition, we strive to look for a cautious value, whose evaluation includes our engineering judgement. While the definition of a characteristic value is often given with the aid of statistics as a fractile value, its determination includes considerations of mechanics because "value" refers to the relevant quantity affecting the limit state. Soils are complex, often spatially heterogeneous and our knowledge of them is typically based on sparse incomplete data. This makes the definition and determination of a characteristic value for soils more multifaceted than for structural materials. This paper discusses the choice of the characteristic value for soils from various perspectives (statistical, mechanistic and practical) and summarises some recent findings to clarify the limitations of existing practice. Overly simplified statistical approaches may lead to unsafe or overly conservative designs. The authors conclude that a balance between practicality and incorporating salient features are needed. By increasing the value of data in design decisions, engineers will be motivated to collect, share, and utilise data as much as possible and bring our practice closer to the digital economy.

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Robustness of Constant Load and Resistance Factor Design Factors for Drilled Shafts in Multiple Strata

Cited by 14 publications

References 5 publications

Reliability evaluation of reinforced concrete columns designed by Eurocode for wind-dominated combination considering random loads eccentricity

Reliability evaluation of reinforced concrete columns designed by Eurocode for wind-dominated combination considering random loads eccentricity

Effect of Number of Soil Strength Measurements on Reliability of Spread Footing Designs

What is a characteristic value for soils?

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