Resistance of Railway Vehicles to Overturning in Gales

Transcription

1 Resistance of Railway Vehicles to Overturning in Gales Signatures removed from electronic version Submitted by D. Boocock Nominated Responsible Manager Approved by J. R. Mitchell Chairman, Traction and Rolling Stock Subject Committee Authorised by K. W. Burrage Controller, Safety Standards Synopsis This standard prescribes design and maintenance requirements for railway vehicles to ensure acceptable resistance against overturning in extreme wind conditions. Safety criteria are related to vehicle aerodynamic shape, weight and mass distributions, suspension characteristics, train speed, routes of operation, and wind speed probabilities. This document is the property of Railtrack. It shall not be reproduced in whole or in part without the written permission of the Controller, Safety Standards. Published by Safety & Standards Directorate Railtrack Railway Technical Centre London Road Derby

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3 Page 1 of 15 Contents Section Description Page Part A Issue record 2 Responsibilities and distribution 2 Implementation 2 Disclaimer 2 Supply 2 Part B 1 Purpose 3 2 Scope 3 3 Definitions 3 4 Overturning Safety Criteria - General Requirements 5 5 Intrinsic Overturning Wind Speed 6 6 Records 8 Appendices A Factors To Be Considered For Overturning Probability Calculations 9 B Technical Commentary 10 References 15 RAILTRACK 1

4 Page 2 of 15 Withdrawn Document Part A Issue record This standard will be updated when necessary by distribution of a complete replacement. Amended or additional parts of revised pages will be marked by a vertical black line in the adjacent margin. Issue Date Comments 1 Jun 94 Original Document (draft was numbered GM/TT0164) Responsibilities and distribution This standard applies to Train Operators that operate or propose to operate railway vehicles on Railtrack lines. Train Operators shall ensure that the provisions of the standard are communicated to all associated organisations and persons with responsibilities for vehicles and suspensions in the fields of technical specification, design, development, procurement, testing, maintenance and Engineering Change. Implementation The provisions of this standard are mandatory. The standard shall apply from 1 October 1994 to all new procurement contracts for new vehicles and to all new programmes involving Engineering Change to existing vehicles. Disclaimer The Safety & Standard Directorate (S&SD) shall use its best endeavours to ensure that the content, layout and text of its standards are accurate, complete and in line with current best practice insofar as is reasonably practicable. It makes no warranties, express or implied, that compliance with all or any of its standards shall be sufficient to ensure safe systems of work or operation. The S&SD will not be liable to pay compensation in respect to the content or subsequent use of its standards, except where it can be shown to have acted in bad faith or there has been wilful default. Supply Controlled and uncontrolled copies of this standard must be obtained from the TDCC Manager, Document Services, Railway Technical Centre, London Road, Derby, DE24 8UP. 2 RAILTRACK

5 Page 3 of 15 Part B 1 Purpose The purpose of this document is to prescribe safety criteria for railway vehicles to ensure safe performance when operating under gale and extreme wind conditions on Railtrack lines. The objective is to minimise the risks of vehicles overturning and ensure safety for passengers, traincrew and others. 2 Scope The requirements of this standard apply to traction and rolling stock (T&RS) vehicles. They also apply to on-track plant that is permitted to undertake movements outside possessions. The requirements apply to: (a) All new vehicles. (b) Existing vehicles undergoing Engineering Change, insofar as the changes materially affect resistance to overturning. (c) Existing vehicles which are proposed for redeployment on other routes, particularly those that include exposed locations. (d) Existing vehicles for which higher maximum operating speeds are proposed. 3 Definitions Cant Deficiency The difference between (i) the angle to which track would have to be canted on a curve to just counterbalance the centrifugal forces acting on a vehicle, and (ii) the actual cant angle of the track. Engineering Change Any alteration or modification to the design of a vehicle that affects its technical performance, particularly where it influences vehicle weight, aerodynamic behaviour or suspension characteristics. Exposed Route A route (or long section of route) which is orientated generally in a northsouth direction and which features hillsides, embankments or viaducts which are open and exposed to south-westerly winds. (Examples of such routes are: West Coast Main Line north of Weaver Junction, and the Cumbrian Coast Line). Gales Extreme wind conditions, specifically wind speeds above 110 km/h as reported by the Meteorological Office. Intermediate Streamlined Vehicle A vehicle which incorporates some of the characteristics of both streamlined and unstreamlined vehicles. (Examples of such vehicles are: Class 87 locomotive, Mark l Coach and Class 155 Sprinter multiple unit). RAILTRACK 3

6 Page 4 of 15 Withdrawn Document Intrinsic Overturning Wind Speed The wind speed that is just sufficient to cause a vehicle to overturn when (i) the vehicle is running within a train formation at its maximum design operating speed on straight and level track, and (ii) the wind is blowing perpendicular to the direction of travel of the vehicle. On-Track Plant All types of mobile rail-mounted plant and machinery that are permitted to undertake movements on Railtrack lines outside possessions. Overturning The situation reached when all the wheels on one side of a vehicle have lost contact with their running rail and the whole weight of the vehicle is supported by the wheels on the other running rail. Overturning Probability The probability that a vehicle will overturn when exposed to gales in conjunction with the normal range of operating speeds and cant deficiencies. Reference Wind Gust Speed The wind gust speed over a specified short time interval that is equalled or exceeded once on average over a specified Wind Return Period at a specified location. Streamlined Vehicle A vehicle characterised by all or most of the following: a smooth continuous body profile which blends with its neighbours; roof corners are rounded; noses on end vehicles are smooth and rounded; bodyside features such as windows, doors, steps and handles are flush-mounted; underbodies are side-faired and bogies or wheelsets are contained within the body profile and may be faired. (Examples of such vehicles are: HST power car and Mark 3 coach). Technically Competent Authority A recognised person or organisation with professional expertise and experience in the aerodynamics of railway or other ground-borne vehicles. (See Appendix B, Paragraph B.7. 1). Unstreamlined Vehicle A vehicle characterised by all or most of the following: extensive discontinuities in body profile with large irregular inter-vehicle gaps; corners are sharp, and extensive bluff surfaces are presented to the wind; doors, steps and handles are mounted external to the body surface; running gear and bogies are exposed. (Examples of such vehicles are: Class 58 locomotive, MGR coal-hopper wagon, and open car-carrier vehicle). Passenger vehicles are excluded from this category. 4 RAILTRACK

7 Page 5 of 15 West Coast Main Line The main railway route between London Euston and Glasgow, via Weaver Junction. Wind Return Period The average period of time in years between occurrences of wind gust speeds equal to or higher than a specified level at a specified location. 4. Overturning Safety Criteria - General Requirements 4.1 Vehicles that operate on Railtrack lines shall be designed and maintained so that they do not overturn when exposed to gales under normal track and operating conditions on those routes where they are permitted to operate. 4.2 A vehicle shall satisfy at least one of the following requirements to ensure its safe operation in gales. (a) The intrinsic wind speed to overturn the vehicle as it runs on straight and level track shall be greater than a prescribed critical value as defined in Section 5. (b) The overturning probabilities for the vehicle when running at its operational speeds and cant deficiencies over its proposed routes of operation shall be determined. A risk assessment shall be carried out to ensure that current safety levels are maintained or improved. This assessment shall be undertaken and endorsed by a Technically Competent Authority. An indicative list of factors to be considered is listed in Appendix A. 4.3 Vehicles shall meet the requirements of this standard over the full range of variations in vehicle condition that are likely to be experienced. Account shall be taken of tolerances in vehicle dimensions, mass distributions and wheel loadings, suspension characteristics, normal variations in vehicle maintenance condition and wear, and any other relevant variables. 4.4 Vehicles shall be maintained so that the prescribed tolerances for components, assemblies and systems that influence overturning resistance are sustained over the lives of the vehicles. 4.5 Deviations from the specific requirements of this standard are permissible providing that an equivalent level of safety is achieved. In such cases, any deviations shall be supported by appropriate technical justification and endorsed by a Technically Competent Authority. RAILTRACK 5

8 Page 6 of 15 Withdrawn Document 5. Intrinsic Overturning Wind Speed 5.1 Except as in Clause 5.3, the intrinsic overturning wind speed for a vehicle in tare condition shall not be less than the minimum acceptable overturning wind speed specified below. Vehicle Maximum Operating Speed (km/h) Minimum Acceptable Overturning Wind Speed Streamlined (km/h) Intermediate (km/h) Unstreamlined (km/h) The intrinsic overturning wind speed for a vehicle shall be calculated using the following formula: V W = G 2 V T d A h f where V W = intrinsic overturning wind speed (km/h) V T = actual train speed (km/h) G = restoring moment due to vehicle weight (N m) d = density of air (1.225 kg/m 3 ) A = total projected side area of vehicle (m 2 ) h = mean height of roof above axle centreline (m) f 1 = aerodynamic factor specified in Clause RAILTRACK

9 Page 7 of The value of the restoring moment G shall be determined from: G = M g b - G o where M =total tare mass of vehicle (kg) g =acceleration due to gravity (9.81 m/s 2 ) b =semi-span of wheelset-to-rail contact points (0.75 m) G o =overturning moment due to lateral and roll (Nm) suspension displacements under wind loading, together with any in-built vehicle weight asymmetry. For vehicles with articulated bogies, or with other forms of weight support arrangements between adjacent vehicles, masses shall be appropriately shared between vehicles for the purpose of calculating the restoring moment G (a) Values for the aerodynamic factor f 1 for trailing vehicles in a train shall be chosen from the following table. Vehicle Type (Trailing) Train Speed Streamlined Factor f 1 Intermediate Factor f 1 Unstreamlined Factor f 1 (km/h) (b) For the leading vehicle in a train, the above aerodynamic factors f 1 shall be further multiplied by the following supplementary factors: Vehicle Type Leading Vehicle Supplementary Factor Streamlined 1.44 Intermediate 1.13 Unstreamlined 0.90 RAILTRACK 7

10 Page 8 of 15 Withdrawn Document 5.3 Where a vehicle is not required, and not authorised, to operate over the West Coast Main Line north of Weaver Junction, or over other Exposed Routes with comparable risks of extreme wind conditions, the minimum acceptable overturning wind speeds may be reduced. In this case, a reduction factor of 0.92 may be applied to the wind speeds listed in Clause Where a vehicle cannot be clearly categorised as streamlined, intermediate or unstreamlined, but lies somewhere between two categories, it is permissible to interpolate values for the minimum acceptable overturning wind speed (Clause 5.1) and the aerodynamic factor f 1 (Clause 5.2.2), providing it is endorsed by a Technically Competent Authority. 6. Records Auditable records of overturning calculations and risk assessments shall be retained and maintained for the life of each vehicle type to demonstrate that the requirements of this standard have been met, and to facilitate any future investigative requirements. 8 RAILTRACK

11 Page 9 of 15 APPENDIX A Factors To Be Considered For Overturning Probability Calculations (a) Aerodynamic characteristics of the vehicle. (b) Weight, mass and suspension characteristics of the vehicle. (c) Speed of operation and cant deficiencies. (d) Position of vehicle in train. (e) Aerodynamic characteristics of adjacent vehicles. (f) Track parameters along the route, particularly line direction, curvature and cant. (g) Reference Wind Gust Speeds along the route. (h) Wind direction probability. (i) Topography of the route. (j) Ground roughness of the land surrounding the route. (k) Height above sea level of the route. (l) Local height of the track above the general level of terrain, and whether the track runs on level ground, on a viaduct, in a cutting or on an embankment. (m) Size of the wind gusts acting on the vehicle, and hence the averaging time over which the wind is measured. (n) Frequency of operation on the route. RAILTRACK 9

12 Page 10 of 15 Withdrawn Document APPENDIX B Technical Commentary B.1 Introduction This commentary explains the technical background to this standard and provides guidance on how the standard should be interpreted and applied within the scope defined in Section 2. B.2 Overturning Safety Criteria B.2.1 Section 4 requires a vehicle to meet at least one of two criteria: (a) the intrinsic overturning wind speed when the vehicle is running on straight track shall be greater than a prescribed critical value. (b) the probability of the vehicle overturning when running on its proposed routes of operation at its normal operating speeds and cant deficiencies shall be sufficiently low to ensure that current levels of safety are at least maintained. This shall be proven and endorsed by a Technically Competent Authority (TCA). B.2.2 Criterion (a) will confirm that a vehicle with a significant safety margin is safe, without incurring excessive costs and the need for validation tests. It is anticipated that most vehicles will meet the standard on the basis of satisfying criterion (a), although inevitably, because the technical issues involved in vehicle overturning are very complex, some vehicles may fail this simple test. In such cases, a vehicle may still be able to meet the standard by taking advice from a TCA concerning the vehicle s particular characteristics, especially its aerodynamic features (see Clause 5.4). If the vehicle still does not meet the standard, it will be necessary to undertake a more detailed analysis as indicated in criterion (b). B.3 Intrinsic Overturning Wind Speed B.3.1 The intrinsic overturning wind speed V W for a vehicle is that wind speed which is just sufficient to cause 100% unloading of the wheels on the windward side of the vehicle, when the vehicle is running in its tare condition at its maximum operational speed on straight track. This wind is considered to blow perpendicular to the direction of travel of the vehicle. The intrinsic overturning wind speed is related to the train speed V T and the resultant wind speed V R by: V W2 + V T2 = V R 2 10 RAILTRACK

13 Page 11 of 15 B.3.2 At the moment of 100% wheel unloading, the aerodynamically induced rolling moment R about the wheel contact points on the lee rail is exactly balanced by the roll restoring moment G due to the weight of the vehicle, that is: R = G B.4 Aerodynamic Rolling Moment B.4.1 The aerodynamic rolling moment is given by the following expression: 2 1 R R = d A h f V where R = aerodynamic rolling moment (Nm) d = density of air (kg/m 3 ) A = vehicle total projected side area (m 2 ) h = vehicle mean roof height above axle centreline (m) V R = wind speed relative to train (km/h) f 1 = aerodynamic rolling moment coefficient factor B.4.2 Values of f 1 that are to be used for estimating intrinsic overturning wind speeds are defined in the table in Clause 5.2.2(a) of the standard. These are based on values which apply to some existing railway vehicles which have had long periods of widespread service in Great Britain. The vehicles are representative of three types of stock with different aerodynamic characteristics. They are the Mark 3 Coach (Streamlined Vehicle); the Derby Lightweight Diesel Multiple Unit vehicle (Intermediate Streamlined Vehicle); and the Freightliner vehicle with empty containers (Unstreamlined Vehicle). The values of f 1 listed for these vehicles are generally conservative. The choice of these vehicles as benchmarks has been constrained by available aerodynamic information on overturning risks and the need to specify vehicles with safe, long-term and country-wide service histories. B.4.3 The values of f 1 specified in Clause 5.2.2(a) are for trailing vehicles. The aerodynamic overturning moment characteristics vary along a train with, in general, the leading vehicle developing the largest values of rolling moment R. For a leading vehicle, a supplementary correction factor has to be applied to the value of the factor for trailing vehicles. The corrections are specified in Clause 5.2.2(b). RAILTRACK 11

14 Page 12 of 15 Withdrawn Document It may not be easy to place some vehicles into the named aerodynamic types, as they may lie between two type descriptions. In these cases, the value of f 1 and the minimum acceptable overturning wind speed may be interpolated, provided it is endorsed by a TCA. More accurate values of f 1 relevant to the actual vehicle under consideration, can be obtained from suitable wind tunnel experiments on a scale model of the vehicle (see B.7.2). For vehicles which are very similar aerodynamically to other vehicles for which values of f 1 already exist, it may be possible to infer new values of f 1 from existing data. Such evaluations must be substantiated by a TCA. B.5 Roll Restoring Moment B.5.1 The restoring moment G due to vehicle mass is to be calculated taking into account the various vehicle body, bogie and wheelset masses and their lateral and roll suspension displacements. (Freight vehicle payloads, even if detachable, are considered to be securely connected for the purpose of this standard, which does not cover loss of load). The restoring moment associated with vehicle mass is thus given by: G = M g b - G o where G = restoring moment due to vehicle mass (Nm) M = total tare mass of vehicle (kg) g = acceleration due to gravity (m/s 2 ) b = semi-span of wheelset-to-rail contact points (m) G o = overturning moment due to lateral and roll (Nm) suspension displacements under wind loading, together with any in-built vehicle weight asymmetry. B.5.2 Where articulated vehicles are used, equivalent values of M and G o need to be determined. These should be based on the specific articulation arrangements adopted and on the degree of mass and stiffness coupling across bogies and between adjacent vehicles. B.6 Application of Standard B.6.1 Combining the equations developed above in B.3.1, B.3.2 and B.4.1, the intrinsic overturning wind speed can be expressed as: V W = G d A h f 1 2 V T RAILTRACK

15 Page 13 of 15 B.6.2 The standard requires that the minimum intrinsic overturning wind speed V w for a vehicle shall not be less than a prescribed value depending on maximum operating speed and degree of streamlining. The minimum intrinsic overturning wind speeds listed in the table in Clause 5.1 are those associated with the benchmark vehicles defined in B.4.2. B.6.3 Coupled with the concept of benchmark vehicles are two quantities which express basic overturning risk. The first is the intrinsic overturning wind speed, which defines under specified operating conditions what wind force and hence what wind speed is required to overturn a vehicle. The second quantity is the statistical chance of that particular overturning wind speed actually occurring on a given stretch of line whilst a train is present. The chosen benchmark vehicles, whilst being relatively light in weight per unit side area, have safe histories of operation over Exposed Routes in Britain. They therefore define benchmarks in terms of actual acceptable levels of risk. Having accepted those levels of risk, their intrinsic overturning wind speeds are adopted as benchmarks themselves. B.6.4 However, for vehicles which are required to operate only over less exposed routes, the application of the benchmark vehicles intrinsic overturning wind speeds would result in a much lower level of risk. This could be unnecessarily restrictive. Therefore, with the aim of equalising risk a reduced value of minimum overturning wind speed is permitted. This is specified by the reduction factor of 0.92 in clause 5.3. Application of this factor to the minimum acceptable intrinsic overturning wind speeds in Clause 5.1 is only acceptable if a vehicle is not required to run over the West Coast Main Line or over other Exposed Routes with comparable risks of encountering extreme wind conditions. B.6.5 The acceptance criterion in Clause 4.2(a) of this standard requires that the intrinsic overturning wind speed V w for a vehicle is greater than a prescribed value. If it is so, no other criteria need be considered. If a vehicle fails to meet this simple criterion, then the probability of the vehicle overturning on its proposed route or routes of operation must be determined and a risk assessment needs to be undertaken to ensure that vehicle operations are at least as safe as current operations, as required by Clause 4.2(b). RAILTRACK 13

16 Page 14 of 15 Withdrawn Document B.7 Supplementary Information B.7.1 Technically Competent Authority A technically competent authority shall have expertise in the aerodynamics of railway or other ground-borne vehicles and be recognised in the United Kingdom or internationally, and may be one of the following: (a) a member or group of staff or a department of a University or similar institution, (b) a research or combined research and consultancy group in private industry, (c) an individual or group within any railway organisation. B.7.2 Aerodynamic Force and Moment Determination The aerodynamic forces and moments which act on a vehicle in a train are usually determined from suitable wind tunnel tests. This is because it is extremely difficult to evaluate these at full-scale due to practical problems of controlling the wind flow upstream of the vehicle and resolving the relevant forces and moments. Theoretical methods, on the other hand, are not yet sufficiently developed to predict reliably the forces and moments. Wind tunnel tests on scale model vehicles, therefore, offer a controllable and repeatable test environment in which to evaluate the aerodynamic forces and moments. In order to model the full scale situation, it is necessary to achieve aerodynamic similarity between the wind tunnel and full scale. This is achieved in part by ensuring that the model is an accurate representation of the full scale vehicle, although some small scale details may not need to be modelled. In addition, to provide correct similitude, the vehicle motion relative to the ground must be accounted for and a correct representation of the upstream wind flow impinging on the vehicle must be provided, both in terms of its gust composition and frequency content. Under certain circumstances it is possible to relax some of these requirements. These tests and the decisions governing how they are undertaken for a particular vehicle are complex and require the control of a TCA. 14 RAILTRACK

17 Page 15 of 15 References None Related documents GM/TT0087 Derailment and Roll-Over. Cooper, R.K. The Probability of Trains Overturning in High Winds. Proc.5th Int.Conf.on Wind Engineering, Colorado USA, July 1979.pp Wind Engineering Data Sheets 82026, 83045, etc. Engineering Sciences Data Unit RAILTRACK 15