BRITISH STANDARD BS AU 210 2 1994 Drawbars for caravans and light trailers — Part 2 Specification for the design of aluminium drawbars and chassis UDC [629 11 43 + 728 76] 629 11 011 1 BS AU 210 2 199[.]
BRITISH STANDARD Drawbars for caravans and light trailers — Part 2: Specification for the design of aluminium drawbars and chassis UDC [629.11-43 + 728.76] :629.11.011.1 BS AU 21 0-2:1 994 BS AU 21 0-2:1 994 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Automobile Standards Policy Committee (AUE/- ) to Technical Committee AUE/8, upon which the following bodies were represented: Association of Trailer Manufacturers British Compressed Air Society Caravan Club Department of Transport National Caravan Council Limited Society of Motor Manufacturers and Traders Ltd Coopted members This British Standard, having been prepared under the direction of the Automobile Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on July 994 © BSI 1 - 999 The following BSI references relate to the work on this standard: Committee reference AUE Draft for comment 92 76306 DC ISBN 80 223 24 Amendments issued since publication Amd No Date Comments BS AU 21 0-2:1 994 Contents Page Committees responsib le Foreword Inside front cover ii Scope References D efinitions Symbols Resistance calculation for drawbars D eflection calculation Fatigue Mechanical design of chassis C hassis strength Joining of b ody to chassis 10 Figure — D rawb ar reference dimensions Figure — Curves relating maximum stress and stress ratio for life cycles Table — Properties of aluminium alloys Table — Permissible stresses for aluminium alloys List of references © BSI 1 - 999 Inside back cover i BS AU 21 0-2:1 994 Foreword This Part of BS AU 21 was prepared under the direction of the Automobile Standards Policy Committee Since the drawbar is only one part of the chassis of a caravan or light trailer, and as the chassis can be made of materials other than steel, or even be of composite construction, this Part of BS AU 21 aims to set out requirements for the design of aluminium chassis for caravans and light trailers A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages to 8, an inside back cover and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover ii © BSI 1 - 999 BS AU 21 0-2:1 994 Scope This Part of BS AU 21 specifies: a) a procedure for determining the mechanical strength of drawbars for caravans and light trailers where the vertical static force on the Symbols For the purposes of this Part of BS AU 21 0, the following symbols are used l is the distance (in mm) from the vertical axis of the coupling device to the first point coupling head is not less than 245 N and not greater than 735 N; b) requirements for the mechanical design of the l on the trailer frame (see Figure ) x axis of the coupling device to the drawbar chassis for caravans and light trailers This standard applies to aluminium chassis of caravans and light trailers provided they are not of welded construction It also covers the aluminium section corresponding to the maximum strain rate (see Figure ) e is the distance (in mm) from the horizontal axis of the coupling device to the drawbar elements of chassis of composite construction, again neutral axis at the first fixing point on the provided the aluminium parts have not been welded NOTE The method for calculation of the mechanical strength of is the distance (in mm) from the vertical e trailer frame (see Figure ) x is the distance (in mm) from the horizontal steel drawbars for caravans and light trailers is covered in axis of the coupling device to the drawbar BS AU 21 0- neutral axis at the cross section References (see Figure ) 2.1 Normative references corresponding to the maximum strain rate d is the maximum deflection (in mm) at the This Part of BS AU 21 incorporates, by reference, coupling device relative to the first fixing provisions from specific editions of other point (see Figure ) publications These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover Subsequent amendments to, or revisions of, any of P D these publications apply to this Part of BS AU 21 This Part of BS AU 21 refers to other publications E standard are listed on the inside back cover, but reference should be made to the latest editions Definitions (see ISO 3853) is the modulus of elasticity (in N/mm ); its value varies according to the alloy that provide information or guidance Editions of these publications current at the time of issue of this is the value determined by calculation for the longitudinal force (in N) occurring between the tractor vehicle and the trailer only when incorporated in it by updating or revision 2.2 Informative references is the manufacturer’s total mass (in kg) of the caravan or light trailer (see ISO 7237) I g (see Table ) is the moment of inertia (in mm4) ) of the section is the acceleration due to gravity (in m/s ) (see ISO 3853) For the purposes of this Part of BS AU 21 0, the definitions given in BS 81 apply, together with the following 3.1 chassis the element, including the drawbar, between the axle assembly and the body of the caravan or light trailer 3.2 drawbar that part of the chassis which enables the connection of the caravan or light trailer to the towing vehicle © BSI 1 - 999 BS AU 21 0-2:1 994 Figure — Drawbar reference dimensions © BSI 1 - 999 © BSI 11-1999 TF H3 H2 TB TF O TF TE TF TB M TF drawn tube extrusions sheet extrusions sheet and plate extrusions extrusions extrusions extrusions extrusions clad sheet clad plate sheet sheet extrusions sheet and plate extrusions sheet and plate sheet and plate extrusions Form 20 150d 3.0 25 6.0 10 150d 25 150d 25 150d 25 150d 20 20 12.5 25 6.0 6.0 25 25 25 25 mm mm — 20 0.2 3.0 — 6.0 — 3.0 — 0.2 — — — — — 3.0 12.5 0.2 0.2 — 0.2 — 0.2 Max Min Thickness 255 270 255 240 255 240 130 — 125 160 110 240 230 370 365 380 130 165 190 170 280 270 295 310 295 295 310 310 280 — 275 185 150 280 370 435 425 440 200 245 300 280 340 320 10 8 — — — 12 — 14 14 8 11 — — — 12 — 8 11 — 13 12-16 7 10 — 4-8 5-8 10 same as tensile 115 150 same as tensile same as tensile tensile 206 118 same as tensile same as tensile 556 525 556 386 324 556 664 772 726 463 494 600 560 660 630 618 587 618 71 700 68 900 68 900 65 500 68 900 72 400 68 900 68 900 800 B 710 B 710 B C 800 Ae 690 A 670 660 A 710 B Elongation 0.2 % 0.2 % Bearing Modulus tensile Tensile of Density Durability proof strength 5.65 Ỉ S0 50 mm compressive strength proof stress elasticityb stress ratingc % % N/mm2 N/mm2 N/mm2 kg/m3 N/mm2 N/mm2 a See BS 1470 b For modulus of rigidity multiply by 0.38 c See BS 8118-1:1991 clause 2.4 d For round tube and hollow sections these properties not apply above 75 mm e C for immersion in fresh or sea water 7020 5251 5154A 2014A 6063 6061 5083 6082 Alloy BS or international Condition no a Table — Properties of aluminium alloys BS AU 210-2:1994 BS AU 21 0-2:1 994 Resistance calculation for drawbars Deflection calculation The calculation for resistance for drawbars shall 6.1 The deflections be carried out over the whole length at the same time as the resistance calculation in l of the drawbar, taking into account distances l and e x x in order to determine the maximum strain rate The strain rate shall be checked at the position where the maximum bending moment occurs when and e=e x d fR shall be calculated, x f x x — For braked trailers: f and — For braked trailers: d Only flexure is taken into account for the calculation M = 36 Pgl fD clause , as follows be calculated as follows NOTE f M (in N·mm) e/l < and e /l < shall The maximum bending moment for the drawbar with l=l d,d fR d +d = 75 ( f fD ) — For unbraked trailers: x — For unbraked trailers: M = 24 Pgl f x The maximum bending moment (in N·mm) for the drawbar with e/l > and e /l x x > shall be d calculated as follows NOTE Only flexure is taken into account for the calculation Three bending moments M, M f fD and M fR shall be calculated and the largest value of the three shall be fR d +d = 75 ( f fD ) The value shall not exceed that defined in 6.2 NOTE Because of the increased flexibility of aluminium compared to steel, it should not be taken for granted that the used for the calculation of the maximum admissible drawbar design is sufficiently stiff without performing a stress deflection calculation M fmax 6.2 The permissible deflection — For braked trailers: M = 36 Pgl M = De M = 75 (M + M f device shall not exceed: x fD d x fR f M = 24 Pgl M = De M = 75 (M + M Because of the constraints on manufacture, all drawbars shall be considered to have type x fR f classification as defined in BS 81 8- : 991 fD ) The permissible stress rates B, calculated for the whole length of the drawbar, shall not exceed the allowed stress B bc to a maximum of 25 mm Fatigue x fD l 70 fD ) — For unbraked trailers: f = d at the coupling (see Table 2) Using the curves in Figure 2, the fatigue life shall be predicted NOTE Bmin is the minimum stress, which is the lower numerical value of the stress in a stress cycle Bmax I/V is the section modulus (in mm ), of the drawbar cross section corresponding to the maximum bending moment NOTE is the maximum stress, which is the higher numerical value of the stress in a stress cycle where It is assumed in this standard that aluminium sheet, plate or strip conforming to BS 470 or bars, extruded round tube Ömin Ömax is the stress ratio, which is the ratio of the minimum to maximum stress in a stress cycle, tensile stress being considered positive and compressive stress negative When these points are plotted on Figure 2a) and Figure 2b) , they always occur on the curve or in the area defined as “acceptable” or sections conforming to BS 474 are used This does not prevent other, suitable and fit for purpose, aluminium alloys being used The properties of some aluminium alloys are shown in Table and Table © BSI 1 - 999 BS AU 21 0-2:1 994 Table — Permissible stresses for aluminium alloys Thickness Alloy BS or international no C ondition Form Min Max mm mm a Axial B Bending B t N/mm b B c N/mm B bt N/mm Shear B bc N/mm N/mm TF 39 39 54 54 83 20 50 47 47 62 62 88 39 39 54 54 83 32 32 47 47 79 40 40 56 56 84 34 34 49 49 80 82 82 96 96 49 01 80 77 94 90 48 01 80 77 94 90 48 01 87 87 96 96 52 39 62 62 69 69 37 117 31 31 45 45 78 01 plate 3 21 — 25 222 sheet and 222 drawn tube M c b N/mm 20 sheet and extrusions — extrusions 6082 B q Bearing — 10 50 d 25 plate 5083 extrusions O sheet and — 50 d 25 plate TF extrusions — 50 TE extrusions — 25 d 6063 6061 d TF extrusions — 50 TB extrusions — 20 35 124 53 42 81 39 extrusions — 20 54 02 54 224 08 78 47 99 47 220 00 61 25 47 07 47 229 01 4A TF clad sheet clad plate 52 51 H3 sheet 75 69 85 79 45 67 51 54A H2 sheet 95 88 07 00 57 78 25 111 111 126 26 67 216 25 00 00 114 114 60 02 25 54 54 71 71 92 38 25 48 48 64 64 89 227 extrusions TB sheet and — plate 702 extrusions TF sheet and — plate a b c d See BS 470 Applies only when buckling is not the criterion; see BS 81 8- Joints in single shear For round tub e and hollow sections the permissible stresses not apply ab ove 75 mm © BSI 1 - 999 Figure — C urves relating maximum stress and stress ratio and life cycles BS AU 21 0-2:1 994 © BSI 1 - 999 BS AU 21 0-2:1 994 Mechanical design of chassis 8.1 Bolted j oints Minimum spacing between bolt holes The spacing between the centres of the bolts shall not be less than 2.5 times the bolt diameter 8.1 Edge distance With extruded, rolled or machined edges, the distance to the edge, measured from the centre of the bolt hole shall not be less than 1.5 times the bolt diameter If, on the beating side, it is less than times the bolt diameter, the permissible beating strength shall be reduced as follows: 8.1 where is the modified bearing strength; is the bearing strength given in Table 2; is the actual ratio of edge distance to bolt diameter; r is the ratio of edge distance to bolt diameter 8.1 Web stiffness The web stiffness shall be demonstrated by calculation as detailed in BS 8118-1:1991, by test or both 8.1 Bolt material Steel bolts conforming to BS EN 24014:1992 and nuts to BS EN 24032:1992 shall be used Both the bolts and nuts used shall be rendered corrosion resistant by zinc plating to BS 3382-2:1961 Washers shall be provided under all bolt heads and nuts and these washers shall be zinc plated to BS 1706:1990 Fe/Zn and passivated The length of the unthreaded part of the bolt shall be such that as far as possible no part of the thread is within the thickness of the member The thread shall project beyond the nut by a minimum of two turns A form of locking device shall be used PBM PB c) painted with priming coat with an inhibiting pigment containing not less than 20 % by weight of zinc chromate or other approved chromate in a suitable water resisting vehicle The priming coat shall not contain any copper or mercury compounds, graphite or carbonaceous materials, or lead; or d) separated by the use of a continuous membrane of non-reactive material e.g plastic NOTE A joint made by any other means not detailed in this standard may be used provided that its load carrying capacity and life expectancy can be shown to be satisfactory 8.3 Contact with timber Aluminium surfaces in contact with timber, unless the timber is fully seasoned and the environment dry and unpolluted, shall be painted Timber in contact with aluminium shall not be treated with preservatives containing copper sulfate, zinc chloride or mercuric salts NOTE Other preservatives may be used provided that it can be shown that the timber so treated is not harmful to the aluminium NOTE Oak, chestnut and western red cedar are likely to be harmful to aluminium particularly where there are through fastenings, unless the timber is well seasoned Chassis strength The chassis manufacturer shall demonstrate, either by test or by calculation, or both, that all elements of the chassis are fit for their declared purpose with reference to BS 8118:1991 Joining of body to chassis The chassis manufacturer shall provide, in writing, instructions in respect of strength and fixing arrangements for the attachment of the caravan or light trailer body to the chassis There shall be no fixing directly or indirectly through the top or bottom flanges of the drawbar at the foremost body fixing position NOTE Other suitable anti-corrosion coatings may be used that adequately protect the jointed parts against electrolytic corrosion (see also 8.3 ) For such composite joints, the steel or cast iron elements shall be either: a) zinc plated to BS 1706:1990 Fe/Zn 8; or b) hot dip galvanized to BS 729:1971; or 8.2 Joints with steel or cast iron © BSI 11-1999 blank BS AU 21 0-2:1 994 List of references (see clause ) Normative references BSI publications BRITISH STANDARDS INSTITUTION, London BS 729:1971, BS 1706:1990, BS 3382, BS 3382-1 & BS 3382-2:1961, BS 8118, BS 8118-1:1991, BS 8118-2:1991, BS EN 24014:1992, BS EN 24032:1992, Sp ecification fo r ho t dip galv anized coatings o n iron and steel articles Method for sp ecifying electrop lated coatings of zinc and cadm ium , on iron and steel Sp ecificatio n fo r electrop lated coatings on threaded com p onents Cadm ium o n s teel com p onents Zinc on steel com p o nents Structural us e of alum inium Code of p ractice fo r design Sp ecification fo r m aterials, w o rkm anship and p rotectio n Hexago n head b olts — Product grades A and B Hexagon nuts, style — Product grades A and B Informative references BSI publications BRITISH STANDARDS INSTITUTION, London BS AU 210, BS AU 210-1:1987, BS 1470:1987, Draw b ars fo r carav ans and light trailers Method o f calculation for the m echanical s trength of steel draw b ars Sp ecification fo r w rought alum inium and alum inium alloys for general engineering p urp oses: p late, BS 1474:1987, p urp o ses: b ars, Sp ecificatio n fo r w rought alum inium and alum inium , ISO 7237:1981, ISO 3853:1977, Strength test © BSI 11-1999 sheet and strip alloys fo r general engineering extruded ro und tub es and sections Road v ehicles — Mass es and dim ensions o f carav ans — Term s and definitio ns Road vehicles — Carav ans and light trailers — Tow ing b rackets and co up ling b alls — BS AU 21 0-2:1 994 BSI — British Standards Institution BS I is the indep endent national b ody res p ons ib le for p rep aring Britis h S tandards It p res ents the UK view on s tandards in E urop e and at the international level It is incorp orated b y Royal C harter Revisions Britis h S tandards are up dated b y amendment or revis ion Us ers of Britis h S tandards should make s ure that they p oss es s the latest amendments or editions It is the constant aim of BS I to imp rove the quality of our p roducts and services We would b e grateful if anyone finding an inaccuracy or amb iguity while us ing this Britis h S tandard would inform the S ecretary of the technical committee res p ons ib le, the identity of which can b e found on the inside front cover Tel: 02 89 96 90 00 Fax: 02 89 96 40 BS I offers memb ers an individual up dating s ervice called PLUS which ens ures that s ub s crib ers automatically receive the lates t editions of s tandards Buying standards O rders for all BS I, international and foreign s tandards p ub lications s hould b e addres s ed to C us tomer S ervices Tel: 899 00 Fax: 899 7001 In res p ons e to orders for international standards , it is BS I p olicy to sup p ly the BS I imp lementation of thos e that have b een p ub lis hed as Britis h S tandards, unless otherwis e requested Information on standards BS I p rovides a wide range of information on national, E urop ean and international standards through its Lib rary and its Technical H elp to E xp orters S ervice Various BS I electronic information s ervices are also availab le which give details on all its p roducts and s ervices C ontact the Information C entre Tel: 02 89 96 71 1 Fax: 02 89 96 048 S ub s crib ing memb ers of BS I are kep t up to date with s tandards develop ments and receive sub s tantial discounts on the p urchase p rice of s tandards For details of thes e and other b enefits contact Memb ership Adminis tration Tel: 02 89 96 70 02 Fax: 02 89 96 00 Copyright C op yright s ub s is ts in all BS I p ub lications BS I als o holds the cop yright, in the UK, of the p ub lications of the international s tandardization b odies E xcep t as p ermitted under the C op yright, D es igns and Patents Act 988 no extract may b e rep roduced, s tored in a retrieval s ystem or transmitted in any form or b y any means – electronic, p hotocop ying, recording or otherwis e – without p rior written p ermis s ion from BS I This does not p reclude the free us e, in the cours e of imp lementing the standard, of necess ary details such as s ymb ols, and size, typ e or grade designations If thes e details are to b e used for any other p urp os e than imp lementation then the p rior written p ermiss ion of BS I must b e ob tained If p ermis sion is granted, the terms may include royalty p ayments or a licensing agreement D etails and advice can b e ob tained from the C op yright Manager BS I 89 C his wick H igh Road London W4 4AL Tel: 02 89 96 70