Section
5 Allowable stresses and safety factors
5.1 General
5.1.1 This Section defines the allowable stresses and safety factors which are required to
be applied to the OPTS and its components.
5.1.2 As an alternative to the allowable stress design method as given in this
Section, the concept of load and resistance factor design may be applied. See
Ch 1, 4.6 Stress factors 4.6.2 and
Table 1.4.1 Conditions, configurations, effects and load
types. The application of the
concept is in general to be carried out as per the requirements of National or
International Standards, such as EN 13001 Cranes – General design. The
application of this alternative concept is to be agreed with LR prior to commencing
of the project.
5.1.3 Alternative approaches to calculate the allowable stresses in this Section will be
specially considered.
5.2 Allowable stresses – Elastic failure
5.3 Allowable stresses – Compression, torsional and bending members
5.4 Overall stability
5.5 Allowable stresses – Plate buckling failure
5.6 Allowable stresses – Buckling failure of thin walled cylinders
5.7 Allowable stresses – Joints and connections
5.8 Rope safety factors
5.8.2 The safety factor as defined in Ch 1, 5.8 Rope safety factors 5.8.1 shall further be
multiplied by a risk coefficient of γn.WR = 1,6. The nominal wire rope
forces shall be evaluated by applying a risk coefficient of γn.DW = 1,1
to the dead load.
5.8.6 Where the reeving system provides some degree of redundancy the rope safety factors
will be specially considered.
5.9 Friction effects
5.9.2 Other friction effects shall also be considered (e.g. sliding telescopic
gangways).
5.9.3 The actual situation, given design and the most unfavourable environmental conditions
shall be considered for the evaluation of the friction coefficients (i.e. the
effects of fluids, moisture, grease, oil, etc.). The friction coefficients shall be
evaluated with the lowest and highest possible friction coefficient in cases where
the integrity of the design depends on the friction coefficient values.
5.9.4 The most unfavourable friction coefficient shall be applied in the design
calculations. It shall be noted that unfavourable coefficients can be the highest or
lowest value. The safety factor for the application of the most unfavourable
friction coefficient shall be 1,5.
5.10 Limit of displacements
5.10.1 The system displacements during overload testing shall be limited as per
Table 1.5.1 Displacements limits. The given displacement limits are related to deformation of
all structural items of the OPTS from pedestal to gangway tip. Displacement limits
for other materials, such as aluminium and composites, will be specially
considered.
Table 1.5.1 Displacements limits
| OPTS
support configuration
|
Primary components, steel
|
| Cantilever
|
|
| Both ends
simply supported
|
|
5.10.2 If the specific design of the OPTS, including the interaction with the
target unit and structure, requires lower displacements, the displacements in Table 1.5.1 Displacements limits
shall be reduced as per the requirements of the designer/manufacturer.
5.10.3 For the calculation of the system displacements in the various
configurations the risk coefficient is not required to be applied. The test loads to
be considered are defined in Ch 1, 13.1 Testing.
5.10.4 Proposals for the application of higher displacements will be specially considered if
it can be demonstrated that those displacements will not result in situations which
impair the usability of the system or which have an impact on the safety of the
personnel to be transferred or any person close to the OPTS including the
Operator.
5.11 Fatigue design assessment
5.11.1 Fatigue calculations are to be carried out in accordance with a
recognised National or International Standard (e.g. ISO 20332 Cranes – Proof of
competence of steel structures, EN 13001 Cranes – General design).
Other standards will be specially considered. The applied standard shall be agreed
with LR.
5.11.2 For these calculations a realistic load collective taking into account
all significant in-service and out-of-service loads and conditions shall be applied.
5.11.3 The lifetime applied for the fatigue assessment shall not be less than
the specified life time of the OPTS.
5.11.4 The proof of fatigue strength shall be carried out for each critical and
primary structural component of the OPTS and the fatigue strength specific
resistance factors γmf (as required in ISO 20332 Cranes – Proof of
competence of steel structures or EN 13001 Cranes – General design)
shall be at least taken as those provided in Table 1.5.2 Fatigue strength specific
resistance factor γmf.
Table 1.5.2 Fatigue strength specific
resistance factor γmf
| Accessibility
|
Fatigue strength specific resistance
factor γmf
|
| Locations readily available for inspection
|
1,2
|
| Locations not readily available for
inspection
|
1,25
|
5.11.5 The risk coefficients as defined in Ch 1, 3.8 Risk coefficient are required
to be applied in the proof of fatigue strength.
|
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