Section 2 Shipboard cranes

2.1.1 This Section applies to shipboard cranes, generally described in Ch 4, 1.2 Lifting appliances and crane types 1.2.1, which are designed to operate in a harbour or sheltered water conditions where there is no significant movement of the ship due to wave action and the significant wave height is not greater than 0,6 m.

2.1.2 The forces and loads acting on the crane structure are to be determined in accordance with the operating and environmental conditions for which the crane is to be certified and must be clearly specified on all crane submissions, together with the speeds of all crane movements, braking times, lifting capacities, ranges, etc.

2.2.1 Consideration is to be given to the utilisation and duty of the particular type of crane or lifting appliance in the ‘inservice’ condition with respect to the following forces and loads:

1. Dead loads.

2. Live loads.

3. Dynamic forces due to the various crane movements.

4. Forces due to ship inclination.

5. Load swing caused by non-vertical lift horizontal movement of the crane and load.

6. Wind forces and environmental effects.

7. Loads on access ways, platforms, etc.

8. Snow and ice when considered relevant.

2.2.2 The crane structure and any stowed arrangements are also to be examined with respect to the stowage condition for the following criteria, as applicable:

1. Forces due to the ship motion and inclination.

2. Wind and environmental effects.

3. Snow and ice.

2.3.1 Cranes are grouped depending on the nature of the duty they perform and each group is designated a duty factor, as given in Table 4.2.1 Duty factor, F _d .

2.3.2 The duty factor, F _d, depends on the frequency of operation and the severity of the load lifted with respect to the appropriate safe working load of the crane concerned and is used to factor both the live and dead load components of loading. The factor assumes normal marine use, operating life not in excess of 6 x 10⁵ cycles and that the crane or lifting appliance has been designed as per the principles of a low susceptibility to fatigue. Consideration is to be given to increasing these values where extra heavy duty is envisaged.

2.3.3 The reduction of the duty factor below the minimum values as in Table 4.2.1 Duty factor, F _d is only permitted if sufficient evidence is provided that the load cycles and the severity of the load spectrum are below the assumed normal marine use. Alternatively, the duty factor may be calculated on the basis of a recognised National or International Standard (e.g. F.E.M. 1.001) upon agreement with LR.

2.3.4 Where appropriate, fatigue calculations are to be carried out in accordance with a recognised National Standard using load cycles and load spectrum agreed between the manufacturer and the Owner.

2.4.1 The basic loads applied to the crane comprise the dead load, L _g, and the live load, L _l, which are as defined in Ch 1 General.

2.5.1 The dynamic forces due to hoisting are those imposed on the structure by shock and accelerating the live load from rest to a steady hoisting speed. To take this effect into account in the design, the live load is multiplied by a hoisting factor, F _h.

2.5.2 The hoisting factor is given by:

2.6.1 Consideration is to be given to the forces which occur when a crane travels along a track or rails resulting in a vertical acceleration acting on the crane and its load together with the horizontal acceleration due to the crane changing speed whilst travelling.

2.6.2 The vertical acceleration is usually small, provided the rail and joints are level and smooth, and since it may be considered that it does not occur at the same time as the maximum dynamic force due to hoisting, it may generally be neglected.

2.6.3 The horizontal acceleration including that due to braking is to be supplied by the manufacturer. Where the acceleration is not available but speed and working conditions are known, the acceleration is to be obtained from the following formulae:

1. For cranes with low travel speed (0,4–1,5 m/s)

   a t

   =

   0,075V t + 0,07

2. For cranes with moderate to high travel speed (1,5–4,0 m/s) and normal acceleration

   a t

   =

   0,075V t + 0,20

3. For cranes with travel speed (1,5–4,0 m/s) and high acceleration (0,4–0,7 m/s²)

   a t

   =

   0,100V t + 0,27

   where

   a t

   =

   acceleration, in m/s2

   V t

   =

   travel speed, in m/s.

   Where the speed is known but working conditions are not, the highest value of acceleration for the appropriate speed is to be used.

2.6.4 In cases where the crane drive control system ensures that motions such as hoisting, travelling or slewing cannot occur simultaneously and the loading caused by one motion is practically zero when the other motion starts, loadings due to hoisting, travelling motions or slewing do not need to be superimposed.

With respect to the load combination formula as given in the Code, this would result in:

where

2.7.1 The inertia forces acting on the load and crane structure resulting from slewing the crane are to be considered.

2.7.2 The slewing acceleration or, alternatively, the slewing speed and braking time, is to be supplied by the manufacturer. Where this is not available, the acceleration at the jib head of the crane, with the crane jib at maximum radius, is to be taken as 0,6 m/s².

2.7.3 The slewing acceleration is to be applied to dead weight and the SWL of the crane. The slewing acceleration is to be taken as 100 per cent of its nominal value up to 40 t SWL and can then gradually be reduced to 50 per cent of its nominal value until 160 t SWL. Beyond 160 t SWL, the slewing acceleration shall remain constant at 50 per cent of its nominal value. The SWL to determine the slewing acceleration is to be taken as the maximum SWL on the load versus radius charts. The graphical representation of the above can be found in Figure 4.2.2 Slewing acceleration.

2.8.1 In general, the effect of centrifugal force acting on the crane structure is small and may be neglected.

2.9.1 Consideration is to be given to racking loads which occur when two pairs of wheels or bogies move along a set of rails and produce a couple formed by horizontal forces normal to the rail direction.

2.9.2 The value of the racking force, F _R, is calculated from the following formulae:

1. C ₂ = 0,05 for values t/b ≤ 2,0

2. C ₂ = 0,025 t/b for values 2,0 < t/b ≤ 8,0

3. C ₂ = 0,20 for values t/b > 8,0

Figure 4.2.3 Equilibrium of forces due to crane travelling along track gives the equilibrium of forces applied to the crane. Alternative calculation methods as detailed in recognised National or International Standards (e.g. F.E.M. 1.001, Booklet 9) may be considered.

2.10.1 Forces applied to the crane structure as a result of the crane coming into contact with buffers are to be considered. Where decelerating devices are fitted which operate before the crane reaches the end of the track, and providing such devices operate automatically and give effective deceleration to the crane at all times, the reduced speed produced by these devices may be used in the calculations.

2.10.2 For cranes where the load is free to swing, the forces are to be calculated equating the energy capacity of the buffer with the kinetic energy of the crane dead weight, i.e. excluding the live load, when the crane is travelling at 0,7 times its design speed.

2.10.3 For cranes where the load is restricted from swinging by rigid guides, the same method is to be used to calculate the forces but the dead weight plus live load is to be used in the calculation.

2.11.1 Shipboard cranes are to be designed to operate safely and efficiently in a harbour or sheltered water environment at an angle of heel of 5° and angle of trim of 2° occurring simultaneously.

2.11.2 Special consideration may be given where it is intended to operate a crane on a vessel at an angle of heel differing from 5° or an angle of trim differing from 2°. Where angles less than these are proposed, evidence is to be provided to demonstrate that such lesser angles cannot be exceeded in service.

2.11.3 In the stowed condition, the crane, its stowage arrangements and the structure in way are to be designed to withstand forces resulting from the following two design combinations:

1. • Acceleration normal to deck of ±1,0g.
   • Acceleration parallel to deck in fore and aft direction of ±0,5g.
   • Static heel of 30°.
   • Wind of 63 m/s acting in fore and aft direction.
2. • Acceleration normal to deck of ±1,0g.
   • Acceleration parallel to deck in transverse direction of ±0,5g.
   • Static heel of 30°.
   • Wind of 63 m/s acting in a transverse direction.

2.11.4 Alternatively, where the crane is to be fitted to a conventional ship and the ship’s characteristics are known, the forces may be calculated using accelerations obtained from consideration of the ship’s motions given in Table 4.2.2 Ship motions, together with the force due to a wind speed of 63 m/s acting in the most unfavourable direction.

2.11.5 The forces due to ship motions are to be determined in accordance with Table 4.2.3 Forces due to ship motions.

2.11.6 The following combinations of static and dynamic forces are to be considered:

1. Rolling motion only:
   • Static roll + dynamic roll + dynamic heave (at roll angle φ).
2. Pitching motion only:
   • Static pitch + dynamic pitch + dynamic heave (at pitch angle ψ).
3. Combined motion:
   • Static combined + 0,8 (dynamic roll + dynamic pitch) + dynamic heave combined.

In each case, the component of force due to wind is to be included where applicable.

2.11.7 Proposals to use other values are to be substantiated by calculations and will be subject to special consideration.

2.12.1 The wind pressure, p, acting on the structure is given by the following formula:

where

The wind speed for the operating condition is to be taken as 20 m/s and for the stowed condition as 63 m/s.

2.12.2 Where it is anticipated that wind speeds in excess of those defined in Ch 4, 2.12 Wind loading 2.12.1 may occur, these higher wind speeds are to be considered.

2.12.3 The wind force acting on the suspended load is to be taken as 300 N per tonne of SWL, but where a crane is to be designed to handle loads of a specific shape and size the wind force is to be calculated for the appropriate dimensions and configuration.

2.12.4 The wind force on the crane structure or individual members of the structure is to be calculated from the following expression:

where

2.12.5 The force coefficient for various structural components is given in Table 4.2.4 Force coefficient (C _f) . The values for individual members vary according to the aerodynamic slenderness and, in the case of large box sections, with the section ratio. The aerodynamic slenderness and section ratio are given in Figure 4.2.4 Aerodynamic slenderness and section ratio.

2.12.6 Where a structure consists of a framework of members such that shielding takes place, the wind force on the windward frame or member and on the sheltered parts of those behind it are calculated using the appropriate force coefficient. The force coefficient on the sheltered parts are to be multiplied by a shielding factor η. The values of η vary with the solidity and spacing ratio of the framework. Values of η are given in Table 4.2.5 Shielding factor (η) for the solidity and spacing ratio as defined in Figure 4.2.5 Solidity ratio and spacing ratio.

2.12.7 Where a structure consists of a number of identical frames or members spaced equidistantly behind each other in such a way that each frame shields those behind it, the wind load is to be obtained from the following expression:

where

2.12.8 For latticed tower structures, the ‘face on’ wind force based on the solid area of the windward face is to be multiplied by the following coefficients:

1. For towers composed of flat-sided sections:

   1,7p (1 + η)

2. For towers composed of circular sections:

   where D V _s < 6,0 m²/s:

   1,1 p (1 + η)

   
   

   and D V _s ≥ 6,0 m²/s:

   1,4 p (1 + η)

where

• The value of η is taken from Table 4.2.5 Shielding factor (η) for a/b = 1,0 according to the solidity ratio of the windward face.

2.12.9 The maximum wind load on a square section tower occurs when the wind blows onto a corner and is to be taken as 1,2 times the ‘face on’ load.

2.12.10 Alternative proposals to calculate the wind load will be considered.

2.13.1 In general, the effects of snow and ice loads acting on the crane structure may be neglected, although they are considered where a particular design or application indicates that these loads are significant.

2.14.1 In general, temperature effects need only be considered with respect to the selection of the steels used in the construction of the crane, see Ch 4, 2.25 Materials.

2.15.1 The crane design is to be considered with respect to loads resulting from the following conditions:

2.15.2  Case 1. For the condition of the crane operating without wind, the design is to be considered with respect to a combination of dead load, live load and horizontal forces defined in Ch 4, 2.6 Dynamic forces due to crane movements to Ch 4, 2.11 Forces due to ship motion, as given by the following expression:

• F _d [L _g + F _h (L _l + L _h1) + L _h2 + L _h3]
• where

2.15.3  Case 2. For the condition of the crane operating with wind, the design is to be considered with respect to a combination of dead load, live load and horizontal forces defined in Ch 4, 2.6 Dynamic forces due to crane movements to Ch 4, 2.11 Forces due to ship motion, together with the most unfavourable wind load. This is given by the following expression:

• F _d [L _g + F _h (L ₁ + L _h1) + L _h2 + L _h3] + L _w
• where

2.15.4  Case 3. The crane is to be considered in its stowed condition when subjected to forces resulting from accelerations due to the ship’s motions and static inclination, together with wind forces appropriate to the stowed condition. (see Ch 4, 2.11 Forces due to ship motion) The effects of anchorages, locks and lashings, etc. are to be taken into consideration.

2.15.5  Case 4. The crane may also need to be considered with respect to the following exceptional load conditions:

1. Coming into contact with buffers.
2. Failure of the hoisting rope during testing or normal operation (F_h, to be taken as –0,3).
3. Sudden release of load during testing or normal operation (F_h, to be taken as –0,3).
4. Test loading.

For heavy lift cranes (or lifting appliances) a risk assessment is to be carried out to evaluate the consequences due to failure of the hoisting rope or sudden release of load and the identified risks are to be mitigated to acceptable levels. The system integrator in cooperation with the manufacturer of the crane and the designer of vessel shall prepare a Safety Statement in line with LR’s ShipRight Procedure Risk Based Certification (RBC) process and/or in line with the requirements of the National Administration (as applicable).

2.16.1 Travelling cranes, trolleys, grabs, etc. which are capable of travelling whilst loaded are to be examined with regard to stability against overturning for the following conditions:

1. The worst operating condition as given by load combination Case 2, including forces resulting from an acceleration at deck level of 0,67 m/s² or maximum acceleration, if known.

2. Consideration of sudden release of load in accordance with load combination Case 2, with the hoisting factor, F_h, taken as –0,3.

2.16.2 The overturning moment is to be not greater than 80 per cent of the stabilising moment.

2.16.3 Travelling cranes, etc. are to be provided with stowage locks or lashings or other means of resisting forces resulting from consideration of load combination Case 3.

2.16.4 Devices used for anchoring the crane or trolley to its track or rails may be taken into account in calculating the stability of travelling cranes only if:

1. Such cranes or trolleys do not travel when loaded.

2. The design of the rail and its anchoring devices are such that stability is achieved by use of efficient wheels and properly designed rails. Alternative devices will be considered.

2.16.5 Consideration is to be given to the following aspects of crane stability:

1. Travelling cranes are to be provided with efficient stops at both limits of travel and are to be designed such that the crane will remain stable after contact with the stops under the most severe operating conditions.

2. Travelling cranes are to be designed to prevent complete derailment or loss of stability in the event of a wheel or axle failure or sudden release of load.

2.16.6 Jib cranes are to be designed such that the jib does not ‘jack-knife’ under operational and test loads. Alternatively, suitable stops may be fitted to prevent the jib from ‘jack-knifing’. Jack-knifing is to be considered using the following expression:

• L _l + L _g + L _h1 + L _h3 + 1,2L _w

The components of the above expression are defined in Ch 4, 2.15 Load combinations 2.15.2.

2.17.1 The allowable stress, σ_a, is to be taken as the failure stress of the component concerned multiplied by a stress factor, F, which depends on the load case considered. The allowable stress is given by the general expression:

where

2.17.2 The stress factors, F, for steels in which σ_y/σ_u ≤ 0,85

where

2.17.3 For steel with 0,85 < σ_y/σ_u ≤ 0,94, the allowable stress is to be derived from the following expression:

where

2.17.4 Steel with σ_y/σ_u > 0,94 will be specially considered.

2.17.5 When the actual yield to ultimate tensile ratio of the material is greater than 0,94, peak stresses beyond the nominal allowable stresses (see Ch 4, 2.17 Allowable stress – Elastic failure 2.17.1 to Ch 4, 2.17 Allowable stress – Elastic failure 2.17.4 and Ch 4, 2.17 Allowable stress – Elastic failure 2.17.6 to Ch 4, 2.17 Allowable stress – Elastic failure 2.17.8) shall be limited to the higher allowable stresses as defined in Ch 4, 2.17 Allowable stress – Elastic failure 2.17.9. Higher peak stresses beyond such a limit will be specially considered, taking into account the actual yield to ultimate tensile strength ratio.

2.17.6 The failure stresses for the elastic modes of failure are given in Table 4.2.7 Failure stress.

2.17.7 For components subjected to combined stresses the following allowable stress criteria are to be used:

1. σ_xx ≤ σ_a

2. σ_yy ≤ σ_a

3. τ_o ≤ τ_a

4. σ_e = ≤ 1,1σ_a

where

2.17.8 The allowable bearing stress for rotatable and fitted pin connections are to be taken as per the allowable bearing stresses for fitted bolts given in Table 4.2.14 Allowable stresses for fitted bolts. The allowable bearing stress for rotatable pin connections with dynamics or loose fit will be specially considered.
Ball and roller bearings are to be in accordance with a recognised National or International Standard.
The allowable bearing stress for other surface-to-surface contact (pressures) is to be taken as in Ch 4, 2.17 Allowable stress – Elastic failure in combination with Table 4.2.7 Failure stress.

2.17.9 In the case where the structural analysis is carried out by means of detailed finite element models, higher allowable stresses may be applied as follows:

1. σ_1.FE≤ 1,1σ_a

2. σ_2.FE≤ 1,1σ_a

3. τ_o.FE≤ 1,1τ_a

4. σ_e.FE≤ 1,1²σ_a

where

Higher allowable stresses, as defined here, may only be applied if the actual stresses are localised. In the case where the actual stresses may also be calculated by means of analytical methods, these higher allowable stresses are not applicable and Ch 4, 2.17 Allowable stress – Elastic failure 2.17.1 is to be applied.

2.18.1 The allowable stress for compression members is to be taken as the critical compressive stress, σ_cr, multiplied by the allowable stress factor, F, as defined in Table 4.2.6 Stress factor, F . In addition to local failure due to the critical compression stress being exceeded, consideration is to be given to the overall ability of crane jibs to resist compression loading, see Ch 4, 2.19 Crane jibs – Overall stability.

2.18.2 For members subjected to simple compression, the critical compression stress is given by the Perry-Robertson formulae as follows:

where

Alternative methods to calculate the simple critical compression stress as per recognised National or International Standards or analysis taking into account second and higher order effects may be considered. In the case where the stability is calculated by means of second or higher order analysis, suitable imperfections are to be taken into account and the loads are to be multiplied by the inverse of the stress factor 1/F where the actual stress results are then to be compared with the yield stress of the component.

2.18.3 The values of Robertson’s constant are given in Table 4.2.9 Values of Robertson’s constant, a, for various sections . The slenderness ratio for members with constant radius of gyration is obtained from the following formulae:

where

For members with varying radius of gyration, an effective radius of gyration is to be calculated in accordance with Ch 4, 2.19 Crane jibs – Overall stability.

2.18.4 For members subjected to combined bending and compression, the following stress criteria are to be used:

where

2.18.5 The effects of ‘lateral torsional buckling’, if applicable to the specific design, are to be taken into consideration by using the methods of recognised National or International Standards, as appropriate.

2.19.1 In addition to individual members of the jib structure being examined with respect to buckling, crane jibs are to be considered with respect to critical compressive failure of the jib as a whole with regard to both plan and elevation planes.

2.19.2 The slenderness ratio is the effective length of the jib divided by the radius of gyration in the plane concerned. To allow for the variation in radius of gyration with length, an effective radius of gyration is to be calculated in accordance with Ch 4, 2.20 Slenderness ratio.

2.19.3 The effective length of the jib is dependent on the constraint conditions at its ends. The conditions are different in plan view from those in elevation and are also dependent on the type of jib concerned, of which there are two types, rope supported and cantilever jibs.

2.19.4 For rope supported jibs, the effective length is to be calculated in the following manner:

1. In elevation, the jib can be considered as being fixed against translation and free to rotate so that the effective length is taken as the actual length of the jib for all jib attitudes, i.e. K = 1,0

2. In plan, the lower end of the jib is to be considered as fixed against translation and rotation by the jib pivots and the head is to be considered as partially constrained with respect to translation by the hoist and luffing ropes, the constraint varying with the tension in these ropes and attitude of the jib. The effective length in plan view is given by

   l

   =

   L K

   where

   l	=	effective length
   L	=	the actual length of the jib
   K	=	a constant equal to
   C	=	is the ratio of load applied to the jib head by the luffing rope to that applied to the non vertical part of the hoist rope, and R, R H, R S, D and H are dimensions, in mm, as shown in Figure 4.2.6 Geometry for jib stability calculations.

2.19.5 The above method is considered satisfactory for conventional jibs. Alternatively, and especially for jibs of slender or very high strength steel designs, the construction is to be analysed taking into account second and higher order effects due to deflection of the structure by iterative or other suitable methods, and calculations submitted. In the case where the stability is calculated by means of second or higher order analysis, suitable imperfections are to be taken into account and the loads are to be multiplied by the inverse of the stress factor 1/F, where the actual stress results are then to be compared with the yield stress of the component.

2.20.1 The slenderness ratio of compression members is given by the general expression, i.e. . For members which have constant area and uniformly varying second moment of area and hence radius of gyration, such as crane jibs, an effective radius of gyration is to be considered. The effective radius of gyration is given by:

where

2.21.1 The allowable stress is to be taken as the critical buckling stress σ_cb, σ_bb, or τ_b, as appropriate, of the component concerned multiplied by the stress factor, F, as defined in Table 4.2.6 Stress factor, F .

2.21.2 For components subject to compression stress, the critical buckling stress is given by:

1. For σ_cb < 0,5σ_y

   

2. For σ_cb ≥ 0,5σ_y

   

   where

   σcb

   =

   critical compression buckling stress

   E

   =

   Young’s modulus

   t

   =

   plate thickness

   b

   =

   plate width, i.e. normal to direction of stress

   a

   =

   plate length

   K c

   =

   compression buckling constant, defined as follows:

   	for α ≥ 1:
   	for α < 1:

   α	=
   μ	=	Poisson’s ratio

   The graphical representation of K _c is provided in Figure 4.2.7 Compression buckling constant K _c .

2.21.3 For components subject to shear stress the critical buckling stress is given by:

1. For τ_b < 0,29σ_y

   

2. For τ_b ≥ 0,29σ_y

   

   where

   τb

   =

   critical shear buckling stress

   b

   =

   smallest plate dimension

   a

   =

   plate length corresponding to b

   Ks

   =

   shear buckling constant, defined as follows:

   	for α ≥ 1:
   	for α < 1:

   α	=
   μ	=	Poisson’s ratio

   The graphical representation of K _s is provided in Figure 4.2.8 Shear buckling constant K _s .

2.21.4 For components subject to bending stress, the critical buckling stress is given by:

1. For σ_bb < 0,5σ_y

   

2. For σ_bb ≥ 0,5σ_y

   

   where

   σbb

   =

   critical bending buckling stress

   b

   =

   plate width, i.e. normal to direction of stress

   a

   =

   plate length, i.e. in the direction of stress

   Kb

   =

   bending buckling constant, defined as follows:

   	for α ≥ :
   	for α < :

   α	=
   μ	=	Poisson’s ratio

   The graphical representation of K _b is provided in Figure 4.2.9 Bending buckling constant K _b .

2.21.5 For components subject to combined compression and shear stress, the following allowable stress criteria are to be met:

1. σ_c ≤ F σ_cb

2. τ ≤ F τ_b

3. 

   where

   τ

   =

   applied shear stress

   σc

   =

   applied compression stress.

2.21.6 For components subject to combined bending and shear stress, the following stress criteria are to be met:

1. σ_b ≤ F σ_bb

2. τ ≤ F τ_b

3. 

   where

   σb

   =

   applied bending stress.

2.21.7 For components subject to combined bending and compression stress, the following allowable stress criteria are to be met:

1. σ_c ≤ F σ_cb

2. σ_b ≤ F σ_bb

3. 

2.21.8 For components subject to combined compression, bending and shear stress, the following allowable stress criteria are to be met:

1. σ_c ≤ F σ_cb

2. σ_b ≤ F σ_bb

3. τ ≤ F τ_b

4. 

2.22.1 The allowable stress is to be taken as the critical buckling stress σ_cb or σ_bb, as appropriate, of the component concerned, multiplied by the allowable factor, F, as defined in Table 4.2.6 Stress factor, F .

2.22.2 For components subject to compression the critical buckling stress is given by:

1. For σ_cb ¹ < 0,5σ_y

   σcb 1

   =

   K'c E

2. For σ_cb ¹ ≥ 0,5σ_y

   

   where

   σcb 1	=	critical compressive buckling stress
   E	=	Young’s modulus
   r	=	average radius of tube
   t	=	wall thickness
   K'c	=	compression buckling constant, see Figure 4.2.10 Compressive buckling constant.

2.22.3 For components subject to bending the critical buckling stress is given by:

1. For σ_bb ¹ < 0,5σ_y

   σbb 1

   =

   K'b E

2. For σ_cb 1 ≥ 0,5σ_y

   

   where

   σbb 1	=	critical bending buckling stress
   K'b	=	bending buckling constant, see Figure 4.2.11 Bending buckling constant.

2.22.4 For components subject to combined compression and bending, the following allowable stress criteria are to be met:

2.22.5 Buckling calculations carried out in accordance with recognised National or International Standards will be considered.

2.23.1 For welded joints, the physical properties of the weld metal are considered as equal to the parent metal. For full penetration butt welds, the allowable stress is equal to the allowable stress of the parent material. (see Ch 4, 2.17 Allowable stress – Elastic failure).

2.23.2 For fillet welds and partial penetration welds, the allowable stresses are reduced. Values of these reduced stresses are given in Table 4.2.13 Allowable stresses in welds. Where F is the stress factor, see Table 4.2.6 Stress factor, F . Figure 4.2.12 Stresses in welds shows the stresses in a typical fillet weld. The actual stress in the fillet welds is to be less than or equal to the allowable stresses and is to be evaluated as follows:

1. Evaluation of perpendicular weld stresses:

   	σ⊥ C–D = τ⊥ D–E ≤ 0,7F σy
   	or
   	σ⊥ D–E = τ⊥ C–D ≤ 0,7F σy

2. Evaluation of longitudinal weld stresses:
   τ_|| ≤ 0,58F σ_y

3. Combined weld stresses

2.23.3 The actual stress in fillet welds is to be calculated on the ‘throat’ dimension a of the weld (see Figure 4.2.12 Stresses in welds).

2.23.4 The strength of joints using pre-tensioned bolts to transmit shear and/or tensile forces, e.g. high strength friction grip bolts, are to be determined in accordance with an appropriate and recognised National or International Standard.

2.23.5 For joints using precision bolts, defined as turned or cold finished bolts fitted into drilled or reamed holes whose diameter is not greater than the bolt diameter by more than 0,4 mm, the allowable stress due to the externally applied load is given in Table 4.2.14 Allowable stresses for fitted bolts.

2.23.6 The allowable stresses for non-fitted bolts are to be taken as per Table 4.2.15 Allowable stresses for non-fitted bolts.

2.23.7 Where joints are subjected to fluctuating or reversal of load across the joint the bolts are to be pre-tensioned by controlled means to 70 per cent to 90 per cent of their yield stress.

2.23.8 Black bolts (ordinary grade bolts) are not to be used for primary joints or joints subject to fatigue.

2.23.9 Carbon steel bolts are to be specified in accordance with ISO 898 part 1. Bolts are to be selected within the range 8.8 to 10.9 (inclusive). Applications for use of 12.9 bolts will be subject to special consideration. Bolt materials in other materials such as stainless steels are to be specified in accordance with a National or International Standard.

2.23.10 Alternative proposals for the calculation of allowable bolt stresses in accordance with an appropriate and recognised National or International Standard will be specially considered. The requirements in the standard need to provide sufficient equivalence to the requirements given in this section and need to be agreed with LR.

2.24.1 The crane manufacturer is to submit plans of the slewing ring, the bolting arrangement, crane and pedestal structure in way of the slewing ring and calculations giving static and fatigue design loads and allowable stresses for the ring and bolting arrangement.

2.24.2 The ring mounting flanges are to be rigid and the bolting equally spaced around the complete circumference of the ring. Mating surfaces are, in general, to be steel to steel and packing material is not recommended between joint faces. Non-equally spaced bolts are only acceptable on the compression side of the crane house. The number of bolts on the compression side shall not be less than half of the number of bolts on the tension side.

2.24.3 Bolts are to be pre-tensioned by controlled means to 70 to 90 per cent of their yield stress. Pre-tensioning is to be in accordance with the bearing manufacturer’s instructions and, in general, pre-tensioning by bolt torqueing up to bolt size M30 may be used. Beyond this, pre-tensioning must be carried out by hydraulic tensioning device and elongation of the bolts measured to determine pre-load. Alternative methods of pretensioning will be specially considered as long as they are reasonably technically equivalent to the above methods.

2.24.4 Slewing ring bolts are to comply with ISO 898-1 and in general not to exceed Grade 10.9. Special consideration may be given to the application of 12.9 bolts where adequate precautions are taken to minimise the risk of hydrogen embrittlement. Threads of all bolt grades are to be rolled after heat treatment to improve fatigue strength.

2.24.5 The load, due to external loading, on the most heavily loaded bolt is given by:

where

Alternative methods for the determination of P will be considered.

2.24.6 The allowable tensile stress for bolts to ISO 898-1 grade associated with the external loading of Ch 4, 2.24 Slewing ring and slewing ring bolting 2.24.5, and pretensioned in accordance with Ch 4, 2.24 Slewing ring and slewing ring bolting 2.24.5, are given in Table 4.2.16 Allowable stress in ISO 898-1 bolts. Alternative methods as described in Ch 4, 2.23 Allowable stress – Joints and connections 2.23.4 may be considered.

2.24.7 The slewing rings are to comply with the Charpy V-notch impact test requirements as per Ch 4, 2.25 Materials 2.25.4, as applicable.

2.25.1 Cranes and submersible lifting appliances are to be constructed of steel which complies with the requirements of Ch 1, 1.6 Materials and fabrication and Ch 11 Materials and Fabrication. Proposals to use materials other than steel will be specially considered. The fabrication is to be in compliance with Ch 11, 2 Fabrication of classed lifting appliances or Ch 11, 3 Fabrication of certified lifting appliances, as applicable.

2.25.2 The selected steel grade is to provide adequate assurance against brittle fracture. The steel is to comply with the Charpy V-notch impact test requirements given in Ch 11, 1.2 General material requirements 1.2.2, with the operating temperature chosen as being the lesser of either that from an assigned winterisation notation or the lowest temperature of operation for the derrick system (see Ch 11, 1.2 General material requirements 1.2.4) .

2.25.3 Slew bearing applications are to be forged materials and are to be delivered in the quenched and tempered condition. Materials typically used for slew bearing applications are 34CrNiMo6 or 42CrMo4 or equivalents. Where other material grades or manufacturing processes are proposed, special consideration will be required.

2.25.4 For worldwide ship operation, slew bearings are to be subject to a Charpy V-notch impact test at room temperature, the minimum average test requirement is 34J. For ship operations below –10°C the Charpy V-notch impact test minimum average requirement is 42J at a test temperature of –20°C.

2.25.5 The required documentation for materials used for the construction of classed and certified cranes and submersible lifting appliances is defined in Ch 11, 4 Material documentation for certified and classed lifting appliances.

2.26.1 The rope safety factor for both running and standing application for cranes with SWL greater than 10 t and less than 160 t is given by:

where

For cranes with SWL ≤ 10 t, SF = 5,0

and SWL ≥ 160 t, SF = 3,0.

This is represented graphically in Figure 4.2.13 Rope safety factor versus crane SWL.
The rope safety factor SF may be reduced for Cases 3 and 4 (see Ch 4, 2.15 Load combinations 2.15.1 and Table 4.2.6 Stress factor, F ) by a factor of .
The safety factor SF for both the luffing and hoisting system is to be determined using the maximum SWL for each reeving arrangement.

2.26.2 The required minimum breaking load of the rope is given by:

where

2.26.3 The ratio of the bottom of the rope groove diameter of the sheave to wire rope diameter is defined in Table 8.3.4 Diameter of sheaves for wire rope in Chapter 8. The radius of the groove sheave is given in Ch 8, 3.3 Materials and construction 3.3.4.

2.26.4 The effects of sheave friction are to be taken into consideration by usually applying 2 per cent for ball or roller bearing sheave and 5 per cent for plain or bushed bearing sheaves. Lower friction values will be specially considered. For the calculation of reeving systems taking into account the effects of sheave friction, see Ch 2, 2.4 Friction allowance.