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Strutures, Safety and Reliability

Recommended Design Fatigue Factors for Reassessment of Piles Subjected to Dynamic Actions From Driving

[+] Author and Article Information
Inge Lotsberg

 DNV, Veritasveien 1, Oslo, 1322 Norway

Gudfinnur Sigurdsson

 DNV, Veritasveien 1, Oslo, 1322 Norwaygudfinur.sigurdsson@dnv.com

Knut Arnesen

 DNV, Veritasveien 1, Oslo, 1322 Norwayknut.arnesen@dnv.com

Michael E. Hall

 ConocoPhillips Norge AS, Ekofiskveien 35, Tananger Stavanger, 4056 Norwaymichael.hall@conocophillips.com

J. Offshore Mech. Arct. Eng 132(4), 041603 (Sep 23, 2010) (8 pages) doi:10.1115/1.4001418 History: Received September 20, 2008; Revised December 16, 2009; Published September 23, 2010; Online September 23, 2010

Calculated probabilities of fatigue failure depend on the analysis procedure used for design. Calculated probabilities of a fatigue failure also depend on long term stress ranges due to loading and uncertainties associated with this. In order to ensure the consistent safety level for assessment of fatigue failure, the design fatigue factors (DFFs) to be used for fatigue design should be dependent on the analysis procedure and premises used. In the present paper, an assessment of appropriate DFFs for piles subjected to dynamic actions from pile driving has been performed by probabilistic analysis based on: uncertainty with respect to dynamic cyclic stress during pile driving, and fatigue capacity of circumferential welds in piles. Accumulated probabilities of fatigue failures in pile butt welds are presented. An assessment of uncertainties involved in calculation of stress ranges during pile driving has been performed. It is shown that the uncertainty in loading when driving records are known is lower than that estimated on the basis of soil data. Thus, in order to obtain consistent safety levels, different DFFs should be used when calculated stress ranges are derived based on soil data only, as compared with the actual stress ranges and number of blows determined from driving records. The results from probabilistic analyses together with recommended design fatigue factors are presented in this paper.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Overview of the driven pile

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Figure 2

Butt weld in pile

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Figure 3

Calculated stress ranges for pile at Ekofisk 2/4 B platform

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Figure 4

Resistance as function of blows counts

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Figure 5

Relative increase in number of cycles as function of relative increase in resistance

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Figure 6

Maximum allowable misalignment in butt welds according to Norsok M-101

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Figure 7

Relation between mean loga values in S-N data and S-N data including misalignment

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Figure 8

Relation between standard deviations in S-N data and S-N data including misalignment

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Figure 9

Probability of failure as function of CoV on nominal stress range in pile with thickness 25 mm

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Figure 10

Probability of failure as function of CoV on nominal stress range in pile with thickness 50 mm

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Figure 11

Probability of failure as function of CoV on nominal stress range in pile with thickness 100 mm

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