Research Papers: Offshore Technology

Fatigue Reliability Analysis for Brace–Column Connection Details in a Semisubmersible Hull1

[+] Author and Article Information
Dilnei Schmidt

Petrobras Research & Development Center,
Rio de Janeiro, RJ 21941-915, Brazil
e-mail: d.schmidt@petrobras.com.br

Lance Manuel

Department of Civil, Architectural and
Environmental Engineering,
The University of Texas at Austin,
Austin, TX 78712
e-mail: lmanuel@mail.utexas.edu

Hieu H. Nguyen

Genesis Oil and Gas Consultants Ltd.,
Houston, TX 77079
e-mail: nhh@utexas.edu

Luis V. S. Sagrilo

Department of Civil Engineering - COPPE,
Federal University of Rio de Janeiro,
Rio de Janeiro, RJ 21941-450, Brazil
e-mail: sagrilo@coc.ufrj.br

Edison C. Prates de Lima

Department of Civil Engineering - COPPE,
Federal University of Rio de Janeiro,
Rio de Janeiro, RJ 21941-450, Brazil
e-mail: edison@coc.ufrj.br

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received March 12, 2015; final manuscript received August 21, 2015; published online September 22, 2015. Assoc. Editor: Colin Chun Fai Leung.

J. Offshore Mech. Arct. Eng 137(6), 061301 (Sep 22, 2015) (7 pages) Paper No: OMAE-15-1027; doi: 10.1115/1.4031493 History: Received March 12, 2015; Revised August 21, 2015

Semisubmersible floating platforms used in offshore deep or ultradeep water environments have hull structures that are comprised of vertical cylinders (columns) connected by braces, pontoons, etc. Several of the connections between these various members are susceptible to fatigue damage. In fatigue damage assessment or fatigue reliability analysis, a global structural response analysis is typically carried out using a finite element (FE) model where internal forces or stresses in the various members are evaluated for specified sea states measured at the site. Of specific interest in the present study is the fatigue reliability analysis of brace-column connection details in a semisubmersible hull unit for selected Brazilian environmental conditions. Stress concentration factors (SCFs) for the selected critical hot spots are applied to the nominal component stresses due to axial forces and biaxial bending. The hot-spot stress response spectra are used with various spectral methods—referred to as Rayleigh, modified Rayleigh (with bandwidth correction), and Dirlik—to estimate fatigue damage using Miner's rule. Uncertainties in some parameters used in the fatigue life assessment are considered and the probability of fatigue failure in the last operational year of the structure is estimated.

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Fig. 1

Semisubmersible hull

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Fig. 2

Local FE model of the brace–column connection

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Fig. 3

Hot-spot locations [5]

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Fig. 4

Flowchart for the overall fatigue analysis

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Fig. 5

Long-term fatigue damage assessment procedure

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Fig. 6

Range of normalized EFL values for different hot-spot locations 1, 4, 7, 19, 22, 10, 13, and 16

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Fig. 7

Range of normalized damage values

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Fig. 8

Normalized Dij (relative to max)

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Fig. 9

Annual (last operational year) probability of fatigue failure



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