Guard rail Check rail
Part 8 Vehicles with Moveable Parts Affecting Stability
8.5 Static stability
8.5.1
Proof of stability against overturning, vehicle stationary, general
8.5.1.1 If a vehicle has a structure that is able to move and affect the static stability, then the proof of stability shall be established by calculation and by testing.
8.5.1.2 If the vehicle is of a design that arrives on site in several pieces, which are then assembled, the assembly operation shall be assessed to check stability under all rail conditions.
In considering the stability of a vehicle, the tests and calculations should be considered for the vehicle during assembly and not limited to the stability of any individual component or sub assembly of the vehicle.
A vehicle is considered stable if, in the most unfavourable structural position, loading, track conditions and wind loading, the centre of gravity does not cross the tipping lines. Guidance for wind loading is set out in EN 280:2001 and EN 13000:2004 which can be used for all vehicles for this aspect.
8.5.2
Calculation for static stability
8.5.2.1 The calculations shall be made for the first of class vehicles only.
It is permissible to use the definition of static stability in G 8.5.1.2.2 for calculation purposes. Testing requirements are set out in 8.5.6 and refer to one and two rail wheels leaving the rail, which is accepted as occurring before the case in G 8.5.1.2.2.
Guidance on the tipping line can be found in ISO 4305:1991 and ISO 10567:1992. It should be borne in mind that the tipping lines set out in these documents are for road wheels and these will be affected by the substitution of rail wheels.
8.5.3
Load cases for calculating stability
8.5.3.1 For vehicles with moveable parts, which may therefore have their centre of gravity displaced or where the wheels can be unloaded, overturning stability shall be calculated. The calculations shall be made with the vehicle on the worst case combination of track cant, twist and gradient set out in 5.2.1.
8.5.3.2 Where the vehicle cannot achieve the required stability on the worst case track conditions, then a limitation of gradient and / or cant is permitted to be applied so that the required stability can be achieved. This limitation shall be shown on the Engineering Acceptance Certificate and in the instruction handbook as set out in 5.5.1.3 and 5.5.6.1.
8.5.3.3 The calculations shall be made in accordance with: a) EN 280:2001for a mobile elevating work platform. b) EN 12999:2011 for a knuckle boom crane. c) EN 13000:2004 for a mobile crane.
d) All other vehicles shall be calculated in accordance with Table 6.
Working mode Use of vehicle Maximum overturning load
With stabilisers On track 1.25P + 0.1F
Without stabilisers On track 1.33P + 0.1F
Parameters P and F in accordance with ISO 4305:1991 and ISO 4310:1981 P = Load including lifting accessories where appropriate
F = Equivalent force of jib or arm / boom(s) Table 6 Load cases for calculating stability
The equivalent force (weight) of the jib ‘F’ is the downward force component of the jib in any particular jib position. A more detailed explanation is set out in ISO 4310:1981.
The stabilisers referred to are the outrigger type. Locking of the suspension is not considered a stabiliser within this meaning.
8.5.4
Rail clamps and stabilisers
8.5.4.1 Rail clamps which could be used to assist in the prevention of overturning shall not be fitted.
8.5.4.2 Overturning stability shall be achieved without the use of any stabilisers coming into contact with the sleepers or rails. The feet of the stabilisers shall be suitable for the types of surface on which they will be expected to operate.
8.5.4.3 The use of stabilisers shall be included in the instruction handbook and shown on the Engineering Acceptance Certificate.
If fitted, stabilisers should be designed so that they do not impinge upon sleepers, either on the track being used for the vehicle or an adjacent track. It is recognised that because of varying track dimensions this requirement is imprecise, but as guidance the stabiliser should normally descend into the ‘six foot’ area between two running lines. It is permissible for the design or use of stabilisers to be made for specific jobs, purposes or locations.
8.5.5
Stability of vehicles when digging or grabbing
8.5.5.1 For use in digging and grabbing overturning stability shall be calculated in accordance with Table 7.
Working mode Duty Standard Maximum
overturning load With or without stabilisers Digging or grabbing ISO 4305:1991 2 P P = Load, including bucket or grab, and contents
Table 7 Load cases for calculating stability of excavators used in digging or grabbing configuration
8.5.5.2 Where the load cannot be shown by a RCI during digging, the calculation shall show the prevention of overturning in this mode. Use of the vehicle for lifting with a grabbing
attachment shall be with an operational RCI. It is permissible for this duty to be a separate duty on the RCI.
Digging is where an open bucket is being used to push into the ground. Grabbing is where a clam shell type bucket is picking up a loose material load (for example ballast). It is recognised that there are many combinations of this type of activity, but the common factor is the combination of reverse loads and potential high transient forces.
The load P includes the contents of the bucket or grab.
Due regard should be made to worst case scenarios for load in bucket and resistance to lifting, for example contacting a solid block whilst scraping soft topsoil.
Consideration should also be given to the increased risk of derailment due to off loading of the rail wheel during digging.
8.5.6
Requirement for testing – proof of stability by test
8.5.6.1 Stability shall be proved by tests as part of acceptance. All foreseeable unfavourable configurations of the vehicle and load, and the worst combination of track cant, twist and gradient set out in 5.2.1 shall be considered. The worst combination shall be taken as the maximum working cant + 20 mm on a 1 in 25 gradient.
8.5.6.2 For multi-piece jib cranes (such as excavators) the first of class vehicle shall be tested for heights, radii, track conditions and boom / jib configurations, with the suspension in static configuration. As a minimum, the following shall be undertaken:
a) Testing shall be completed on flat level track (that is without gradient, cant or twist) at 10° intervals around the vehicle, with the main boom in mid position.
b) Testing shall be completed on track with a combination of maximum gradient, twist and cant at 10° intervals around the vehicle in the worst case, with the main boom in mid position.
c) At the worst angular position per duty sector, the tests shall be repeated on track conditions (a) and b) above) at three radii (maximum, minimum and mid-point), at three heights (maximum, minimum and mid-point) with the main boom as far back as possible and then as far forward as possible. The maximum height is permitted to be limited in certain positions by the necessity to maintain backward stability. Where the RCI does not have duty sectors the additional testing shall be carried out at 10° intervals.
d) In addition to level rail and maximum cant, the tests shall be repeated for at least one intermediate cant value.
e) Where the vehicle is to be restricted to a lesser value of gradient or cant (as permitted by 8.5.6.3) the tests in a) to d) above shall be undertaken with these lesser values and combination of lesser values.
8.5.6.3 The results obtained in 8.5.6.2 shall be compared with the calculated results. Where there is correlation to within 5% then no further testing is required. Where there are differences between calculated and actual results further testing shall be carried out in the specific area of the discrepancy to verify the test results obtained.
For single piece jib cranes the testing set out in 8.5.6.2 is recommended but without the different heights; the load should be kept as low to the ground as possible during these tests.
It is not essential that specific radii or heights are tested; it is important that an accurate value of radius or height is measured and sufficient values are tested. For example, when testing at various radii it does not have to be at 5.00 m and 6.00 m, other values such as 4.91 m and 6.13 m are acceptable. Subsequent identical vehicle are allowed to be tested on flat level track, directly over each end and at the worst angular position as shown by the first of class vehicle. The tests are permitted to consist of maximum, minimum and mid radii at maximum, minimum and mid height. Providing the tip test results obtained are within 5% of the values of the first of class vehicles, no further testing is required.
8.5.6.4 The testing shall be carried out in accordance with: a) EN 280:2001 for a mobile elevating work platform. b) EN 12999:2011 for a knuckle boom crane.
c) EN 13000:2004 for a mobile crane.
d) All other vehicles shall be tested in accordance with Table 8.
8.5.6.5 If the maximum overturning load set out by Tables 6 and 8 cannot be achieved on the worst case track conditions, it is permissible to use more favourable values of track cant and gradient. In this case a notice shall be displayed on the vehicle indicating the maximum cant and gradient on which the vehicle is permitted to be used; this shall be displayed on the data panels, where fitted, (see Appendix C). Such limitations that need to be placed on the operation of the vehicle to enable safety and stability shall be clearly shown on the Engineering Acceptance Certificate and in the instruction handbook.
Working mode Load condition Maximum safe working load
Without stabilisers Static in working mode SWL = 90% of load that causes first rail wheel to leave the rail or 75% of the load that causes the second rail wheel to leave the track, whichever is the less With stabilisers Static in working mode As per manufacturer’s specification. As
a minimum this shall verify the calculated result from Table 8. ‘Leave the rail’ is defined as the point at which the rail wheel unloads completely Table 8 Static stability
All the tests referred to in 8.5.6.1 to 8.5.6.3 should be carried out by continuing to lift increasingly heavy loads, or applying heavier loads, as appropriate, until the first rail wheel is completely unloaded.
There is no defined means for detecting when the wheel is unloaded but a simple method is to have a thin steel shim between wheel and rail; when the shim can be pulled out is the point the wheel is unloaded. Having noted the load for the first wheel to be unloaded, continue lifting until a second rail wheel becomes unloaded. If the vehicle has bogies the second wheel should be on a different bogie to the first wheel that lifted.
The method of determining the safe working load by test for a vehicle with stabilisers in use cannot be specified because of the variety of designs and potential radii. The manufacturer should demonstrate that the tests
completed demonstrate the theoretical calculations set out in 8.5.3.3 and are comparable with similar tests for the vehicle without stabilisers.
Where the safe working load in the tests set out in 8.5.6.4 is found to be greater than the value of P used in the calculations in 8.5.3.3, the calculations should be repeated using the higher value of P.
8.5.6.6 When changing from stabilisers ‘used’ to ‘not used’, it shall not be possible to change from one configuration to the other if this would cause the load moment to reach or exceed the safe working load for the new configuration.
Where powered stabilisers are used, the controlling switch should be inhibited where the load would be greater than that allowed without stabilisers.
8.5.7
Backward stability
8.5.7.1 In working mode it shall not be possible for any rail wheel of the vehicle to become unloaded. For vehicles exceeding 5 t gross vehicle weight the minimum wheel loading shall not be less than 500 kg. The wheel load shall be controlled at all times during working operations unless the design of vehicle shall make unloading impossible.
8.5.7.2 All subsequent vehicles of the same type shall be tested on the worst case values of track cant, gradient and twist, with the most adverse boom position to check the minimum wheel load is within 5% of the value of the first of class vehicle with the identical main boom angle setting.
The first of class vehicle should be tested on flat level track and then the tests repeated on each of the track conditions set out in 5.2.1, using all possible boom configurations to check the worst case scenario is used. This normally results in a main boom angle being discovered which should not be exceeded.
Where backward stability is constantly monitored by a load sensing device it is permissible for the main boom angle to vary, but there should be a system in place to prevent sudden reductions in load causing the vehicle to become backwardly unstable.
Backward stability tests should be carried out with nothing attached to the boom, for example no lifting accessories or even a quick hitch (unless permanently attached to the vehicle and shown as such on the Engineering Acceptance Certificate and in the instruction handbook). See also the requirements for consumables set out in 8.8.