Appendices

111

Combination  factors  for  the  superposition  of  wave,  water  current  and  ice  occurrences  are  not
listed  in  DIN  EN  1990.  As  an  alternative  to  the  undiminished  superposition  of  the  individual
occurrences  listed,  actions  from  the  combined  occurrence  of  waves,  water  currents  and  ice
with  a  50-year  cycle  may  be  used  in  the  estimate.  In  order  to  superimpose  the  individual  actions ­
  as  per  DIN  EN  1990  [1],  [2]  by  means  of  leading  and  accompanying  actions,  it  is  necessary ­
  to  ensure  that  an  integral,  action-related  partial  safety  factor  of  at  least  1.35  is  adhered  to
for  the  normal  or  extreme  action  combination.

Appendix  5-IV  Application  notes  on  DIN  EN  1993-1-9  -  fatigue  verifications
5-IV.1  General  information  and  partial  safety  factors
The  verifications  in  the  fatigue  limit  state  shall  always  be  conducted  according  to  DIN  EN
1993-1-9  [6]  using  either  the  nominal  stress  concept  or  the  structural  stress  concept.  Which
concept  is  used  -  damage  tolerance  or  adequate  safety  margin  against  fatigue  failure  without
any  prior  indication  -  depends  particularly  on  the  feasibility  of  planned  periodic  inspections.
The  partial  safety  factors  y Mf  shall  be  selected  accordingly  along  the  lines  of  [6]  from  Table
5-IV.1.

Accessibility/execution  of  periodic
inspections

Damage  tolerant  or  minor
damage

Not  tolerant  to  damage  or
major  damage

Good  accessibility,  periodic
inspections

1.00

1.15

No  or  poor  accessibility,  no  periodic
inspections*

1.15

1.35

*  It  shall  be  assumed  that  the  accessibility  to  all  components  which  are  permanently  under  water  is  poor,  for  example.

Table  5-IV.1:  Partial  safety  factors  in  the  fatigue  verification
Contrary  to  what  is  stated  in  the  regulations  in  [6],  a  threshold  value  for  the  fatigue  strength
shall  not  be  used  when  the  number  of  load  cycles  N  >  10 8 .
In  contrast  to  what  is  stated  in  [6],  the  recommendations  of  MW  [15]  Section  3.5.2.1.  state  that
the  dependence  of  the  fatigue  strength  on  effects  of  the  metal  sheet  thickness  should  be  taken ­
  into  account.
Using  the  notch  detail  definitions  according  to  [6]  assumes  that  all  components  have  a  functioning ­
  corrosion  protection  system.  The  requirements  in  accordance  with  chapters  B2.2.1,
B2.3.1  and  Annex  6  shall  be  complied  with  in  this  case.  Depending  on  the  achievable  lifetime
of  the  corrosion  protection,  the  design  shall  include  allowances  to  the  calculated  metal  sheet
thicknesses  in  the  vicinity  of  the  splash  zone.
In  addition,  the  regulations  of  DNV  [17]  may  be  used  for  the  fatigue  verification.  This  can  be
particularly  useful  when  there  is  no  comprehensive  corrosion  protection  as  stated  above  and
the  correspondingly  modified  stress  number  curves  are  used.

5-IV.2  Structural  stress  concept
The  fatigue  verifications  for  welded  nodes  of  hollow  sections  can  be  conducted  solely  according ­
  to  the  structural  stress  concept.  The  stress  concentration  factors  required  for  this  shall
be  determined  separately  for  all  verification  points  with  the  aid  of  finite  element  calculations  or
from  parametric  equations.  Relevant  notes,  e.  g.  [15]  Section  2.2.3.4,  can  be  obtained  to  ext-