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DNV-OS-C501 Composite Components
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SECTION 8
Safety-, Model- and System FactorsSec.8
A. Overview of the various factors
used in the standard
Sec.8
A 100 General
Sec.8 A
101 The safety factor methodology used in this standard is presented
in section 2 C600.
Sec.8 A
102 The Table A1 shows the various safety factors, model factors
and system factors used in this standard.
Sec.8 A
| Table A1 overview
of the various factors used in the standard |
| Symbol | Designation | Reference | Type |
| gF | Partial load effect factor | section 8 B | safety factor |
| gM | Partial resistance factor | section 8 B | safety factor |
| gFM (= gF x gM) | Combined load effect and resistance factor | section 8 B | safety factor |
| gSd | Load model factor | section 8
C | model factor |
| gRd | Resistance model factor | section 8 C | model factor |
| gS | System factor | section 8
D | model factor |
| gfat | Partial factor for fatigue analysis | section 8
E | safety factor |
Sec.8
B. Partial load effect and resistance
factors
Sec.8
B 100 General
Sec.8 B
101 The following two partial safety factors are defined in this
standard (see section 2 C600):| — | partial
load effect factors, designated by gF |
| — | partial resistance factors,
designated by gM. |
Sec.8 B
102 In some cases it is useful to work with only one overall safety
factor. The uncertainties in load effects and resistance are then
accounted for by one common safety factor, the combined
load effect and resistance factor, denoted gFM, which in many cases comes
about as the product of gF and gM: gFM = gF x gM
Sec.8 B
103 Partial load effect factors gF are applicable to the local response
of the structure. They account for uncertainties associated with
natural variability in the local responses of the structure (local
stresses or strains) from its characteristic values. The factors
are selected based on the distribution
type and coefficient of variation (COV).
Sec.8 B
104 The distribution type and COV of the local response are linked
to the uncertainties in the loads applied to the structure, the
transfer function and the type of structural analysis that was carried
out. If the transfer function and
structural analysis are linear, the local load effect distribution
type and COV will be the same as those of the globally applied loads.
If non-linearity is involved in either the transfer function or
the analysis, the distribution type and or the COV may change. In
such a case, the distribution and the COV shall be determined for
the local response.
Sec.8 B
105 Partial resistance factors gM account
for uncertainties associated with variability of the strength.
Sec.8 B
106 The partial load effect and resistance factor gFM. = gF x gM in this standard is calibrated
against different target reliabilities. These target reliabilities
correspond to annual probabilities of failure. The calibration has
been performed under the assumption of a design rule equal to the
one given in section 2 C606, for
which the requirement to the partial safety factors in order to
meet a specified reliability requirement is a requirement to their
product.Sec.8
B 200 How to select the partial safety
factors
Sec.8 B
201 The safety factor gFM depends
on the following:| — | target
reliability level, expressed in terms of annual probability
of failure |
| — | characteristic values for
load effects and resistance, in this standard, there
is only one option for definition of characteristic load effect
(see section 3 I400) and one for the
definition of characteristic resistance (see section
4 A600) |
| — | type of distribution function
for load effects and resistance, in this standard a
normal distribution is assumed for resistance, whereas several options
are given for the load effect distribution type. |
| — | coefficient of variation
(COV) for load effect and for resistance. |
Sec.8 B
202 The required target reliability level in this standard depends
on the following:| — | the limit state (ULS or SLS) |
| — | the safety or service class |
| — | the failure type (brittle, plastic or ductile). |
Sec.8 B
203 The target reliabilitiy levels shall be selected from section 2.
Sec.8 B
204 The full set of partial safety factors is shown in the tables in
B 500. As an alternative, a simplified set of partial safety factors
can be used (see B300 and B400).Sec.8
B 300 Simplified set of partial safety
factors (general)
Sec.8 B
301 A simplified set of partial safety factors is given for use whenever
a satisfactory probabilistic representation of the load effects,
as required in section 3 I200,
is not available.
Sec.8 B
302 The characteristic load effect shall be defined as the 99% quantile
in the distribution of the annual extreme value of the local response
of the structure, or of the applied global load when relevant (see section 9 A400). It shall correspond
to the 100-year return value.
Sec.8 B
303 The simplified set of partial safety factors given in this standard
is determined under the assumption that the coefficients of variation
of load effects are not larger than 20%. These partial
safety factors shall not be used for load effects with a COV larger
than 20%.
Sec.8 B
304 The simplified set of partial safety factors shall be used when
the characteristic resistance is defined as the 2.5 % quantile
in the distribution of the resistance.
Sec.8 B
305 Table B1 shows the simplified set of partial safety factors gFM = gF x gM.Sec.8 B
| Table B1 Simplified
set of partial safety factors gFM = gF x gM for general load effects.(Factors
should only be used with loads defined as the 99% quantile as
described in 302) |
| Safety Class | Failure Type | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Low | Ductile/Plastic | 1.2 | 1.3 | 1.4 |
| Brittle | 1.3 | 1.4 | 1.6 |
| Normal | Ductile/Plastic | 1.3 | 1.4 | 1.6 |
| Brittle | 1.5 | 1.6 | 2.0 |
| High | Ductile/Plastic | 1.5 | 1.6 | 2.0 |
| Brittle | 1.7 | 1.9 | 2.5 |
Sec.8
B 400 Simplified set of partial safety
factors (for known maximum load effect)
Sec.8 B
401 A simplified set of partial safety factors is given for use whenever
a maximum load effect is known that absolutely cannot be exceeded.
No extreme value of the specified load effect can under any circumstance
be higher than the load effect value used in the design.
Sec.8 B
402 The simplified set of partial safety factors given in this standard
is determined under the assumption that the coefficients of variation
of load effects are 0%. The simplified set of partial safety
factors shall be used when the characteristic resistance is defined
as the 2.5 % quantile in the distribution of the resistance.
Sec.8 B
403 The Table B2 shows the simplified set of partial safety factors gFM = gF x gM. Sec.8 B
| Table B2 Simplified
set of partial safety factors gFM = gF x gM for known maximum load effects |
| Safety Class | Failure Type | COV of the strength |
| | | COV £ 5 % | 10 % | 12.5 % | 15 % |
| Low | Ductile/Plastic | 1.07 | 1.16 | 1.26 | 1.36 |
| Brittle | 1.11 | 1.28 | 1.41 | 1.60 |
| Normal | Ductile/Plastic | 1.11 | 1.28 | 1.41 | 1.60 |
| Brittle | 1.15 | 1.40 | 1.62 | 1.96 |
| High | Ductile/Plastic | 1.15 | 1.40 | 1.62 | 1.96 |
| Brittle | 1.18 | 1.53 | 1.86 | 2.46 |
Sec.8
B 500 Full set of partial safety factors
Sec.8 B
501 When a satisfactory probabilistic representation of the load
effects, as required in section 3 I200,
is available, the full set of safety factors may be used instead
of the simplified set.
Sec.8 B
502 The full set of partial factors is shown in appendix E. It shall
be used with a characteristic strength defined as the 2.5 % quantile
value. These factors depend on the properties described in 201.Sec.8
B 600 Partial safety factors for functional
and environmental loads as typically defined for risers
Sec.8 B
601 If loads are defined as functional and environmental loads
as commonly done in offshore applications as described in Section
3I306, the partial factors in Table B3 should be used.Sec.8 B
| Table B3 Partial load
effect factors gF |
| Limit
state | F-load effect | E-load effect | |
| gF1) | gE2) | |
| ULS | 1.1 | 1.3 | |
| FLS | 1.0 | 1.0 | |
NOTES- If the functional load effect reduces the combined load
effects, gF shall be taken
as 1/1.1.
- If the environmental load effect reduces the combined
load effects, gE shall
be taken as 1/1.3.
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Guidance note:
Functional loads are defined as mean loads in Table B3.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.8 B
602 The resistance factors applicable to ultimate limit states (ULS)
are specified in the Tables B4 and B5. The factors are linked to
the safety class to account for the consequence of failure.Sec.8 B
| Table B4 Brittle failure
type - Partial resistance factor |
| Safety Class | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Low | 1.22 | 1.33 | 1.49 |
| Normal | 1.34 | 1.53 | 1.83 |
| High | 1.47 | 1.75 | 2.29 |
Sec.8 B
| Table B5 Ductile/Plastic
failure type - Partial resistance factor |
| Safety
Class | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Low | 1.11 | 1.16 | 1.23 |
| Normal | 1.22 | 1.33 | 1.49 |
| High | 1.34 | 1.53 | 1.83 |
Sec.8 B
603 The resistance factors applicable to serviceability limit states
(SLS) are specified in the Table B6. The factors are linked to the
safety class to account for the consequence of failure.Sec.8 B
| Table B6 SLS - Partial
resistance factor |
| Safety
Class | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Normal | 1.11 | 1.16 | 1.23 |
| High | 1.22 | 1.33 | 1.49 |
Sec.8
B 700 Partial safety factors for functional
and environmental loads as typically defined for TLPs
Sec.8 B
701 If loads are defined as functional and environmental loads
as commonly done in offshore applications for Tension Leg Platforms
(TLPs) as described in Offshore Standard DNV-OS-C105 'Structural
Design of TLPS' , the partial factors in Table B7 should
be used.Sec.8 B
| Table B7 Partial load
effect factors gF |
| | Load
categories |
| Combination of design
loads | Permanent and functional
loads | Environmental loads | Deformation loads |
| a) | 1.2 * | 0.7 | 1.0 |
| b) | 1.0 | 1.3 | 1.0 |
| * ) If the load
is not well defined e.g. masses or functional loads with great uncertainty,
possible overfilling of tanks etc. the coefficient should be increased
to 1.3. |
Guidance note:
Functional loads are defined as mean loads in Table B7.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.8 B
702 The loads shall be combined in the most unfavourable way,
provided that the combination is physically feasible and permitted
according to load specifications. For permanent loads, a load factor
of 1.0 in load combination a) shall be used where it gives the most
unfavourable response. Other considerations for the partial coefficients
are given in DNV-OS-C101.
Sec.8 B
703 The resistance factors applicable to ultimate limit states (ULS)
are specified in the Tables B8 and B9. The factors are linked to
the safety class to account for the consequence of failure.Sec.8 B
| Table B8 Brittle failure
type - Partial resistance factor |
| Safety
Class | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Low | 1.35 | 1.46 | 1.63 |
| Normal | 1.48 | 1.68 | 2.01 |
| High | 1.62 | 1.93 | 2.51 |
Sec.8 B
| Table B9 Ductile/Plastic
failure type - Partial resistance factor |
| Safety
Class | COV of the strength |
| COV < 10 % | 10 %-12.5 % | 12.5 %-15 % |
| Low | 1.22 | 1.27 | 1.35 |
| Normal | 1.35 | 1.46 | 1.63 |
| High | 1.48 | 1.68 | 2.01 |
Sec.8
C. Model factors
Sec.8
C 100 General
Sec.8 C
101 The following two types of model factors
are defined in this standard:| — | load
model factors, designated by gSd |
| — | resistance model factors,
designated by gRd . |
Sec.8
C 200 Load model factors
Sec.8 C
201 Load model factors gSd account
for inaccuracies, idealisations, and biases in the engineering model
used for representation of the real response of the structure, e.g.
simplifications in the transfer function (see
section 9 A800). Effects of geometric tolerances shall also be included
in the load model factor. The factor is treated here as a deterministic
parameter.
Sec.8 C
202 Details about the load model factor are given in section 9 L. The factor shall make
up for uncertainties and inaccuracies in the transfer function,
the analysis methods, and dynamic effects.Sec.8
C 300 Resistance model factors
Sec.8 C
301 Resistance model factors gRd account
for differences between true and predicted resistance values given
by the failure criterion.
Sec.8 C
302 Model factors shall be used for each failure criteria. The factors
are given in Section 6 for each failure criterion. A summary is
given in Table C1.Sec.8 C
| Table C1 Summary of
model factors |
| Failure Criterion | Model factors gRd | Reference |
| Fibre Failure | 1.0 or gA | 6-C202 |
| Matrix Cracking | 1.0-1.15 | 6-D100-400 |
| Delamination | 1.0-2.0 | 6-E |
| Yielding | 1.0 | 6-F |
| Ultimate failure of orthotropic homogenous
materials | 1.25 | 6-G |
| Buckling | Same range as all other criteria. | 6-H |
| Displacements | 1.0 | 6-I |
| Stress Rupture | 0.1-1.0 | 6-J400 |
| Fatigue | 0.1-1.0 | 6-K300 |
Sec.8
D. System effect factor
Sec.8
D 100 General
Sec.8 D
101 The safety factors are given for the entire system. Depending
on how the components are connected to form a system, the target
probability of failure for individual components may need to be
lower than the target probability of failure of the entire system.Guidance note:
E.g. In the case of a pipeline system, the failure of one
pipe component (i.e. plain pipe or end connector) is equivalent
to the failure of the entire system. This is a chain effect. As
a consequence, the target safety of individual components should
be higher than the target safety of the entire system, in order
to achieve the overall target safety.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.8 D
102 In order to take this system effect into account, a system effect
factor gS shall
be introduced. If the system effect is not relevant, gS = 1.0. Otherwise a
system factor shall be documented. A value of gS = 1.10 can be used
as a first approach.
Sec.8 D
103 In some cases a system may consist of parallel components
that support each other and provide redundancy, even if one component
fails. In that case a system factor smaller than 1 may be used if
it can be based on a thorough structural reliability analysis.Sec.8
E. Factors for static and dynamic
fatigue
analysis
Sec.8
E 100
Sec.8 E
101 Table E1 shows the factors gfat shall
be used for the prediction of failure due to cyclic fatigue or due
to long term static loads. The factors shall be used with the failure
criteria in section 6 J and K.Sec.8 E
| Table E1 Factor for
fatigue calculations gfat |
| Safety class |
| Low | Normal | High |
| 15 | 30 | 50 |
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