2.1 General
2.1.1 This Section applies to cargo and vehicle lifts which are operated whilst the ship is in a harbour or sheltered water environment, and where cargo or vehicles may be stowed on them in their stowed position whilst the ship is at sea, i.e.
Standard Service Category.
2.1.2 Where the lift is designed to operate in conditions other than those defined in 2.1.1, the design is to be subject to special consideration, i.e. Specified Service Category.
2.1.3 The operating and stowed loading conditions are to be clearly specified in all submissions together with hoisting speeds, and braking times.
2.1.4 For the operating condition the lift is to be considered with respect to the following forces and loads:
(a) Self-weight of lift.
(b) Applied loading.
(c) Dynamic forces due to hoisting/lowering.
(d) Forces due to static inclination of the ship.
2.5 Design loads
2.5.1 The design loads are to be consistent with the ship's loading manual and are to include the details of the number and spacing of vehicles the lift is designed to accommodate, the type of vehicles, their weight, axle loading, tyre print dimensions, and number and spacing of wheels and supports. Fig. 5.2.1 gives typical loading information. Due account is to be taken of asymmetric loading where applicable.
2.5.2 In addition to vehicle loading the lift is to be considered with respect to uniform deck loading (UDL) appropriate to the deck or decks at which it is stowed and is to comply with the appropriate requirements of Pt 3, Ch 3 and Chapter 11 of LR's Rules for Ships. Similarly where the lift forms part of the ship's watertight structure it is to comply with these requirements as appropriate.
2.6 Load combinations
2.6.1 The lift is to be considered with respect to design loads resulting from the following conditions:
(a) Case 1 Operating condition.
(b) Case 2 Stowed condition.
(c) Case 3 Test load condition.
2.6.2 Case 1. The lift is to be considered with respect to the self-weight and applied load multiplied by a dynamic factor of 1,20, together with the horizontal forces as defined in 2.4.2. This is represented by the following expression:
1,2 (Lw + Lc) + Lh1+ Lh2 where
Lw = self-weight load Lc = applied load
Lh1 = factored load due to 5° heel Lh2 = factored load due to 2° trim.
2.6.3 Case 2. The lift is to be considered with respect to the forces resulting from the accelerations due to ship motion, together with the forces due to consideration of static inclination as defined in 2.4.3 or 2.4.4 together with weather forces appropriate to its stowed position.
2.6.4 Case 3. The lift is to be considered with respect to forces due to the self-weight plus the test load, Lt, multiplied by a dynamic factor of 1,20. This case is represented by the following expression:
1,2 (Lw+ Lt) where
Lt = SWL x proof load factor obtained from Ch 9,1.9.
2.7 Allowable stress – Elastic failure
2.7.1 The allowable stress,σa, 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:
σa = Fσ where
σa = allowable stress, in N/mm2 F = stress factor
σ = failure stress, in N/mm2.
2.7.2 The allowable stress factor, F, for steel in which
≤0,7, is to be as given in Table 5.2.1:
where
σy = yield stress of the material stress, in N/mm2 σu = ultimate tensile strength of the material, in N/mm2.
2.7.3 For steel with > 0,7, the allowable stress is to be derived from the following expression:
σa = 0,41F (σu+ σy)
2.7.4 The failure stresses for elastic failure are given in Table 5.2.2.
2.7.5 For components subject to combined stresses the following allowable stress criteria are to be met:
(a) σxx< F σt (b) σyy< F σt
(c) τo< F τ
(d) (σxx2+ σyy2– σxxσyy+ 3τo2)1/2< 1,1F σt
where
σxx = applied direct stress in x direction, in N/mm2 σyy = applied direct stress in y direction, in N/mm2
τo = applied shear stress, in N/mm2.
2.8 Allowable stress – Plate buckling failure 2.8.1 The allowable stress is to be taken as the critical buckling stress of the component concerned multiplied by the stress factor, F, as defined in Table 5.2.1. The critical buckling stress is obtained by reference to Ch 3,2.22.
σy σu
σy σu
Section 2
Table 5.2.2 Failure stress
Mode of failure Symbols Failure stress
Tension σt 1,0σy
Compression σc 1,0σy
Shear τ 0,58σy
Bearing σbr 1,0σy
Table 5.2.1 Stress factor, F
Load case Case 1 Case 2 Case 3
Stress factor, F 0,60 0,75 0,85
NOTE
Where the lift forms part of the hull structure the scantlings are to comply with the requirements of the Rules for Ships.
17,5t
2650
260 370
370
2000 260 8850
944010 700
12 300
30t 2100 750
55t
30t 30t (20t + 10t) 20t
20t 20t
4500
TW 67,5t
TW 50t
TW 70t
TW 100t
TW 102t
TW 181t
TW 200t All are 1600 4000
11 700 12 200
75002500 2500
2900
55t 570
1090
2100
20t
600 81
20t
300 81
20t
317 263
31t
410 56
65t
350 56
16,75t 16,75t
240 310 2650
3300
5200 3655
1500 65t
10 000
9600
700 900
65t 1000
33,5t on each wheel
20t 20t 20t 20t 20t
31t 31t
40t
Section 2
Fig. 5.2.1 Typical loading data
2.9 Required deck plating thickness
2.9.1 The deck plating thickness, t, is to be not less than:
t = 4,6 A Pw + 1,5 mm where
A = stress factor obtained from Fig. 5.2.2 for the tyre print and plate dimensions defined in the figure Pw = load, in tonnes, on the tyre print. For close-spaced
wheels the shaded area shown in Fig. 5.2.2, may be taken as the combined wheel print.
2,0
For intermediate values of tyre print ratio and plate panel ratio the stress factor A is obtained by interpolation
u v Plate panel ratio =
Plate panel ratio = 1,0 Tyre print ratio ≥ 2,5
le
2.10.1 The deflection of the lift structure or of any individual member with respect to Case 1 and 2, see 2.6.2 and 2.6.3, is to be limited to:
mm where
l = distance between supports, in mm.
2.10.2 Where applicable the deflection is to be limited to ensure the watertight integrity of the ship is maintained.
2.11 Guide rails
2.11.1 Arrangements are to be provided to restrict horizontal movements of the lift during operation by guide rails, or other means.
2.11.2 Where guide rails are fitted they are to be such that the maximum deflection, resulting from horizontal components of load, is not greater than 6,0 mm. The working clearance between the lift and guide rail is to be such as to allow free vertical movement of the lift.
2.12 Stowage locks
2.12.1 Stowage locks are to be provided to resist the vertical, forward/aft and lateral loads as defined in 2.6.3.
Arrangements are to be such that the locks do not work loose and impair the watertight integrity of the ship.
2.13 Hoisting arrangements
2.13.1 Where chains are used as part of the hoisting arrangement they are to have a minimum safety factor of 4,0.
2.13.2 Where wire ropes are used as part of the hoisting arrangement they are to have a safety factor given by:
SF =
but not less than 4,0 nor greater than 5,0.
where
SF = minimum safety factor required L = safe working load of lift
This is represented graphically in Fig. 3.2.11 in Chapter 3.
2.14 Materials
2.14.1 Materials are to comply with the requirements of Chapter 8.
2.14.2 Where the lift is a classification item the material is to comply with Ch 8,1.1 and the grade of steel selected in accordance with Table 3.5.2 in Chapter 3.
104 8,85L + 1910 l
400
Section 2
Fig. 5.2.2 Deck plating stress factor, A
2.14.3 Where the lift is subject to certification only, the material is to comply with Ch 8,1.2. The selected steel grade is to provide adequate assurance against brittle, fracture taking into account the material tensile strength and thickness and the environment in which the lift is designed to operate and, in general, is to comply with the Charpy test requirements given in Table 3.2.17 in Chapter 3.