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.

References

References
1.
Det Norske Veritas
,
2013
, “
SESAM User Manual. WADAM: Wave Analysis by Diffraction and Morison Theory
,” Høvik, Norway.
2.
Det Norske Veritas
,
2014
, “
Fatigue Design of Offshore Steel Structures
,” Recommended Practice DNV-RP-C203, Høvik, Norway.
3.
ISSC
,
1964
, “
Report of Committee 1 on Environmental Loads
,”
2nd International Ship Structures Congress
, ISSC, Delft, The Netherlands.
4.
Haver
,
S.
,
1980
, “
Analysis of Uncertainties Related to the Stochastic Modeling of Ocean Waves
,” Doctoral thesis, NTNU, Trondheim, Norway.
5.
Det Norske Veritas
,
1993
, “
SESAM Theoretical Manual, Framework, Steel Frame Design
,” Høvik, Norway.
6.
Vugts
,
J. H.
, and
Kinra
,
R. K.
,
1976
, “
Probabilistic Fatigue Analysis of Fixed Offshore Structures
,”
Offshore Technology Conference
, Houston, TX, Paper No. OTC 2608.
7.
Marshall
,
P. W.
,
1977
, “
Preliminary Dynamic and Fatigue Analysis Using Directional Spectra
,”
J. Pet. Technol.
,
29
(
6
), pp.
715
722
.
8.
Wirsching
,
P. H.
, and
Light
,
M. C.
,
1980
, “
Fatigue Under Wide Band Random Stresses
,”
J. Struct. Div., ASCE
,
106
(
7
), pp.
1593
1607
.
9.
Dirlik
,
T.
,
1985
, “
Applications of Computers in Fatigue Analysis
,” Ph.D. dissertation, University of Warwick, Coventry, UK.
10.
Det Norske Veritas
,
2005
, “
Riser Fatigue
,” Recommended Practice DNV-RP-F204, Hovik, Norway.
11.
Ragan
,
P.
, and
Manuel
,
L.
,
2007
, “
Comparing Estimates of Wind Turbine Fatigue Loads Using Time-Domain and Spectral Methods
,”
Wind Eng.
,
31
(
2
), pp.
83
99
.
12.
Det Norske Veritas
,
2000
, “
Fatigue Reliability of Old Semi-Submersibles
,” HSE, OTO Report No. 2000 052.
13.
Mršnik
,
M.
,
Slavič
,
J.
, and
Boltežar
,
M.
,
2013
, “
Frequency-Domain Methods for a Vibration-Fatigue-Life Estimation-Application to Real Data
,”
Int. J. Fatigue
,
47
, pp.
8
17
.
14.
Wirsching
,
P. H.
, and
Chen
,
Y. N.
,
1988
, “
Consideration of Probability-Based Fatigue Design for Marine Structures
,”
Mar. Struct.
,
1
(
1
), pp.
23
45
.
15.
Almar-Naess
,
A.
,
1985
,
Fatigue Handbook: Offshore Steel Structures
,
Tapir
,
Trondheim, Norway
.
16.
Melchers
,
R. E.
,
1999
,
Structural Reliability Analysis and Prediction
,
2nd ed.
,
Wiley
,
New York
.
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