Guidelines for High Strength Friction Grip Bolts

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Research Design and Standards Organization, Lucknow Report no BS-111 (Revision 5) Guidelines for use of High Strength Friction Grip (HSFG) bolts on bridges on Indian Railways

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Foreword to BS-111 (Revision 5) HSFG bolts are being adopted on steel bridges widely since last two years and this document is being referred for guidance by the field as well as design engineers. An important feedback was received from field that the Quality Control of bolts is not covered properly in the earlier versions of the report even though the codal references had been given. To address this issue, a new annexure V has been added to specify not only the tests

required for quality control but also their frequency and their independent verification etc. It is hoped that this will help the field engineers in ensuring the quality of bolts. Few other changes in this document i nclude: 1.

A & C slip no 10 of IRS B1 has been issued which incorporates the provisions regarding DTI washers and length of bolts, which were already included in this report vide Revision 4. Accordingly, the references have been changed to reflect the same.

2.

IS:1367 Part 8 has revised version 2012 has been incorporated for torque to be given in the nuts.

3.

The FAQs have been numbered Annexure III and Do’s and Don’t as Annexure IV. RDSO extends hearty thanks for Mr Avadhesh and Mr Gautam Bose from M/S Panchsheel Fasteners, Mr

Rupesh Patel from M/S Loyal Enterprises And Mr Sumit Kumar Udehra from M/S Udhera Mechanical Works who have given feedback on the report which has formed the basis of the changes in the document. The Inspection wing for steel girders at RDSO (B & S as well as M & C dtes) have also given their feedback on practicality of provisions, whose contribution is acknowledged here. All the users, designers as well as field engineers are once again requested to give further feedback on HSFG bolts to RDSO at e mail ID [email protected] so that the codal provisions can be improved and practical difficulties, if any, in implementing the guidelines are taken care of.

Executive Director (B&S) RDSO

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Foreword to BS-111 (Revision 5) HSFG bolts are being adopted on steel bridges widely since last two years and this document is being referred for guidance by the field as well as design engineers. An important feedback was received from field that the Quality Control of bolts is not covered properly in the earlier versions of the report even though the codal references had been given. To address this issue, a new annexure V has been added to specify not only the tests

required for quality control but also their frequency and their independent verification etc. It is hoped that this will help the field engineers in ensuring the quality of bolts. Few other changes in this document i nclude: 1.

A & C slip no 10 of IRS B1 has been issued which incorporates the provisions regarding DTI washers and length of bolts, which were already included in this report vide Revision 4. Accordingly, the references have been changed to reflect the same.

2.

IS:1367 Part 8 has revised version 2012 has been incorporated for torque to be given in the nuts.

3.

The FAQs have been numbered Annexure III and Do’s and Don’t as Annexure IV. RDSO extends hearty thanks for Mr Avadhesh and Mr Gautam Bose from M/S Panchsheel Fasteners, Mr

Rupesh Patel from M/S Loyal Enterprises And Mr Sumit Kumar Udehra from M/S Udhera Mechanical Works who have given feedback on the report which has formed the basis of the changes in the document. The Inspection wing for steel girders at RDSO (B & S as well as M & C dtes) have also given their feedback on practicality of provisions, whose contribution is acknowledged here. All the users, designers as well as field engineers are once again requested to give further feedback on HSFG bolts to RDSO at e mail ID [email protected] so that the codal provisions can be improved and practical difficulties, if any, in implementing the guidelines are taken care of.

Executive Director (B&S) RDSO

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All the users, designers as well as field engineers are once again requested to give further feedback on HSFG bolts to RDSO at e mail ID [email protected] so that the codal provisions can be improved and practical difficulties, if any, in implementing the guidelines are taken care of.

Executive Director (B&S) RDSO ********* Foreword to BS-111 (Revision 3) HSFG bolts are evolving field for Indian Railways. Since the version 2 was issued, HSFG bolts have been included in Indian Railway Codes vide: 1)

Correction Slip No. 19 to IRS Steel Bridge Code.

2)

Correction Slip no. 6 to IRS B1-2001.

3)

Correction Slip no. 27 to IR Bridge Manual.

4)

Correction Slip no. 20 to IRS Steel Bridge Code.

5)

Correction Slip no. 9 to IRS B1-200

The codal/manual provisions shall apply to HSFG bolts. This report may be referred to as explanatory handbook only and in case there is any contradiction, the codes/manuals will prevail. This third revision of BS-111 has been necessitated to give guidance regarding torque to be applied for tightening of bolts. The correction slips already issued have been referenced as required. Special thanks to field engineers giving feedback, especially Girish Kumar Rao, AXEN/Con, Visakhapatnam, E. Co. Railway. All the users, designers as well as field engineers are once again requested to give further feedback on HSFG bolts to RDSO at e mail ID [email protected] so that the codal provisions can be improved and practical difficulties, if any, in implementing the guidelines are taken care of.

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Foreword to BS-111(Revision1) The guidelines for use of High Strength Friction Grip Bolts (HSFG) on bridges on Indian Railways was issued in June-2012. This is a new field for Indian Railways and lots of issues have been raised by the users, designers and field engineer s. There has been need to modify certain provisions to ensure smooth field working and so a need for revision in the original guidelines issued has arisen. The following major changes have been made in the revised guidelines:1. In para 7.II. the nominal diameter of hole has been changed from 2mm to 1.5mm more than bolt diameter for bolts having diameter less than 25mm and 2mm more than the bolt diameter for larger diameter bolts. This para has been added so that hole diameter is same as used for rivets. 2. Para 8, sub-para VII has been modified to cover different cases of provision of washers in field including DTI washers as old provisions were creating some confusion. 3. In para 10.I.c). a sub-clause vi is added describing Personnel for Tightening. This para has been added for better quality control. 4. In para 10.II.b).iv, the 0.1mm feeler gauge has been specified to be used for checking and term refusal has been defined. 5. In para 12.II.(c), the para regarding use of HSFG bolts for repair/rehabilitation work has been reworded to make it more clear. 6. In para 12.III, the para on painting has been replaced by a para specifying Painting during initial installation and Painting in service. This is as per feedback received.

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Foreword Steel is an important material for construction of bridges. The connections in shop are now being made by submerged arc welding. But for field connections, rivets have been traditionally used. The riveted connections have served us well for over 150 years. But the rivets pose some difficulties: 1.

In difficult and inaccessible areas, making rivets is difficult and often quality of rivets in such

locations is very poor. 2.

For large grips, longer rivets are required. The shanks of these rivets are difficult to be heated

uniformly and while transporting the hot rivets, the same get differentially cooled and the rivets are not able to completely fill up the annular space all round. 3.

With changing times, Indian Railways and the only major organization in India still using

structural rivets and the availability of skilled labour required for riveting is diminishing. RDSO has been seized of these issues and has been looking for replacement of the rivets with some other type of connections and High Strength Friction Grip (HSFG) bolts have been found suitable for the same. These can be used in road bridges as their use has been permitted by IRC codes. For railway bridges, the relevant codes are required to be changed (clauses pertaining to design of HSFG bolts for railway loading need to be introduced) before the HSFG bolts can be used for the same. While preparing these guidelines IS codes, Eurocodes, American codes and literature on the subject have been referred. The drawings issued by zonal railways incorporating HSFG bolts for ROBs were also studied. RDSO has tried to make the guidelines comprehensive and cover the design, installation and maintenance aspects in the same. The concerns of engineers about theft and sabotage have also been

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Basics about HSFG Bolts 1. Introduction: Rivets have been used historically for making field connections in steel girders subject to railway and highway loadings. Rivets, however, require skilled workers and elaborate equipment/arrangements. With passage of time, the availability of such labour and equipment for small quantum of work is becoming difficult and Indian Railways (IR) is looking for alternatives to rivets. Also, rivets are difficult to make when the grip length increases as the uniform heating of longer rivets and also ensuring that rivets do not cool down before the same is driven becomes problematic in field. One option for substitute for rivets, namely High Strength Friction Grip (HSFG) bolts is covered in these guidelines. HSFG bolts are high strength structural bolts which have been tightened such as to induce predefined tension in the bolt shank. Due to the tension in the bolt, the interface between the plies (steel members in a joint) cannot move relative to each other because of the frictional resistance. The bolts act differently than normal bolts or rivets as explained below:

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For actual design/ use, the source codes shall be referred to and followed. These guidelines cover the use of HSFG bolts in Road Over Bridges as well as Railway Bridges. At the moment, IRC codes allow use of HSFG bolts and with issue of correction slips to codes for incorporating provisions related to HSFG bolts, HSFG bolts can be used as an alternative to the rivets in all types of railway bridges. RDSO is modifying all standard drawings from rivets to HSFG bolts. Due to different actions, HSFG bolts cannot be used in conjunction with rivets/ welds in same joint without considering the structural action 3. Hierarchy of Codes: The guidelines have been prepared based on IS and EN codes, with modifications to suit the conditions for Indian railways. The hierarchy of codes shall be as follows: I.

Provisions of IRS codes.

II.

Where IRS codes are silent, relevant IS codes may be referred.

III.

Where both IRS and IS codes are silent, EN codes may be referred.

4. Reference Codes: I.

IS 4000: 1992 – High Strength Bolts in Steel structures – code of Practice.

II.

IS 3757 – 1985 (reaffirmed 2003) – Specifications for high strength structural bolts.

III.

IS 6623:2004 - High Strength Structural Nuts - Specifications

IV.

IS 6649:1985 - Specification for Hardened and Tempered Washers for High Strength Structural Bolts and Nuts.

V.

IS 1367 (Part 8): 2012 –Prevailing Torque type Steel Hexagon Nuts - Mechanical and

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symbol. Alternately, marking ‘8.8 S’ or ‘10.9 S’ are also acceptable. The suffix ‘S’ here denotes that the bolt is high strength structural bolt with a large series hexagon.

(a)

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IV.

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Length: The length of bolt shall be chosen such as to hold the steel members in position, with provision for the nut, washer(s) and some projection beyond the bolt. Along with the overall length of the bolt, the thread length has to be specified. At least 4 full threads shall remain clear between the bearing surface of the nut and unthreaded part 3

of the shank (This means that at least 4 threads shall extend into the members being joined by the bolt). The minimum length of bolt shall be worked out on the basis of maximum grip length covering maximum limits of ply thickness (covering ply thicknesses and all washers minus one standard washer) plus an additional allowance 4 given in table 1 of IS 4000. Table 1 of IS 4000 is reproduced below:

Nominal Size of Bolt M 16 M 20 M 24 M 30 M 36

Nominal Dia of Bolt 16 20 24 30 36 Table 1 of IS 4000

Allowance for Grip in mm 26 31 36 42 48

For M 22 bolts, the allowance for grip shall be 34 mm. Most manufacturers have ready tables for the bolt lengths depending upon the steel plates to be gripped. Still, it will be prudent on the part of the field engineer to cross check the computations before ordering the bolts. Maximum grip length of all plies, including packings and packing

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6

and then tempered at a temperature of at least 425 C. Normal height of nut shall be more than 0.8 times the nominal bolt diameter. II.

Identification of Nut: The nuts have the following markings:

7

a)

Manufacturer’s identification symbol.

b)

Property class, marked as ‘8S’ or ‘10S’. (The suffix ‘S’ denotes a high strength

structural nut with a large series hexagon.) Alternately, ‘8.8 S’ or ‘10.9 S’ are also acceptable.

Fig: Typical markings on nuts The marking shall be either on the top or the bottom face of double chamfered nuts and shall be either indented or embossed on non bearing surface of washer faced nuts. III.

Surface of Nut: All nuts shall be supplied with coating consisting of zinc phosphate that is used in conjunction with suitable oil of r ust preventive type as per IS:1367 (Part XII).

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III.

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Oversize Holes: In case the bolts are to be provided in existing structure, the maximum size of hole shall not exceed 1.25 d or d + 4 mm whichever is less i.e. for 16 mm dia bolt, the maximum diameter of hole shall not exceed 20 mm and for 24 mm dia bolt, the maximum diameter shall not exceed 28 mm.9

IV.

Use of Hardened Washers: In case the hole diameter exceeds the bolt diameter by 2 mm, hardened washers shall be used i n place of normal washers.

8. Washer: Annular rings which are provided between the bolt head/ nut and the members being joined are called washers. Washers for HSFG bolts shall conform to IS 6649. The washers have the following characteristics: I.

Types: Three types of washers have been specified in IS 6649, clause 2: a)Type A: Plain hole circular washers. b) Type B: Square taper washers for use with channels (60 taper) 0

c) Type C: Square taper washers for use with I-beams (8 taper)

Identification: Type A washers shall be identified by provision of two nibs (small projections) and manufacturer’s identification symbol in indented character. The type B and C washers shall be identified by the type identification symbol, B or C and the manufacturer’s identification symbol.

Nib

10

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b) Packing washers: If the bolt is longer than required, plain washers may be used as packing washers. However, the maximum number of packing washers shall be

limited to 3, with maximum total combined thickness of 12 mm.11 c) Hardened washer: For oversize holes, hardened washers shall be used.12 These washers are required to prevent punching of the nut in the annular space around the bolt shank.

Note: IS 6649 specifies only one type of washers, which are through hardened and 13

tempered , so all the terms a), b) and c) above refer to the same type of washer only. d) Tapered Washer: Where the angle between the axis of bolt and the joint surface is more than 3 degree off normal, a tapered washer shall be used against the tapered surface. Non rotating surface shall preferably be placed against tapered washer.14 III.

Surface Finish: All washers (except DTIs) shall be supplied with coating consisting of zinc phosphate that is used in conjunction with suitable oil of rust preventive type as per IS 1367 (Part XII).

IV.

Dimensional Deviation for washers: All washers shall be flat with a maximum deviation not exceeding 0.25 mm from straight edge laid along a line passing through the center of the hole.

V.

15

Direct Tension Indicators (DTI): The Direct Tension Indicators are special type of washers with projections which get pressed when tension is applied. The pressing of projections to required level indicates that the required tension has been applied in the

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10.9.Suitable markings identifying the bolt manufacturer, property class of DTI and its diameter shall be engraved suitably on the DTI. Action of DTIs is as indicated below:

Two faces of DTI

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DTI side to protect the projections from damage due to the abrasion during bolt tightening. The same is shown in figures below: Stationary Head/nut

Moving Nut/Head

Stationary Head

9. Surface preparation for steel interface before providing HSFG bolts: The steel interface between the plies which form a joint having HSFG bolts shall have special surface preparation so that sufficient slip factor as assumed by designer in design is available. The following surface preparation shall be done: I.

New construction: The interface between the plies which are connected together by the HSFG bolts shall be “Aluminium metallised without any over coating ”. The aluminium 17

metallising shall be as per para 39.2.1 of IRS B1.

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The effort through the tightening procedures is to lead the bolt into the horizontal part of the bolt tension/ elongation curve as shown above.

Fig: Manual Torque wrenches of two different sizes b) Tension to be given: The bolt shall be tightened to minimum loads specified in

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only).These bolts shall not be tightened to second stage till all the bolts in a joint are inserted and tightened to first stage. iii.

After the alignment/ geometry of members is verified to be correct as per drawings, balance bolts shall be inserted and tightened upto first stage of tightening. The drifts inserted as above shall also be replaced by HSFG bolts one by one.

iv.

The final tightening shall not proceed until the gap between the plates has been closed such that the residual gap, if any, is less than 2 mm at edges.20 There shall, however, be no gap in the central portion. In case the central portion is not in close contact or gap at edges is more than 2 mm, straightening of members may be done after opening out the bolts inserted and the entire procedure i) to iii) above shall be repeated.

v.

During tightening of bolts also, the steel members can continue to deform and hence the tightening of subsequent bolts can lead to loosening of already tightened bolts. In order to minimize the loosening of already tight bolts, tightening in the two stages 21

shall be done starting from the stiffest part to the free edges. Stiffest parts of joint

generally towards the center of the joint. Bolt tightening

for

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satisfactory, a competency certificate shall be issued by an engineer not below the rank of ADEN or equivalent. The competency certificate once issued shall be valid for six months. Any person deployed for installation of HSFG bolts must possess a valid competency certificate.

II.

Procedure for Installation of HSFG Bolts Using Direct Tension Indicator: This is the preferred method of installation of HSFG bolts.

a) Calibration of Direct Tension Indicator: Before the DTI are brought to site, the same shall be tested in the presence of engineer. Three nos. bolts of similar diameter and property class as shall be used in the work shall be taken and installed with DTI. The installation procedure to be followed shall be similar to the one given for plain washers. On full tightening, the projections on DTI washers shall meet the requirements of checks specified after second stage tightening using DTIs. Only the

DTIs which satisfy the calibration shall be brought to site for work. b) Procedure:22The tightening is done in two stages so that the bolts already tightened do not get loose when the subsequent bolts are tightened. i. First Stage of Tightening: As a first stage, all bolts in the joint shall be tightened to ‘snug tight’ condition. Snug tight condition means the nut is tightened using an ordinary wrench by an average worker, applying maximum force on the wrench. This stage is required to bring the plies in close contact. ii. Checks after First stage tightening: After first stage of tightening, the joint shall be

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9 5 *No more than 10% of the indicators in a connection bolt group shall exhibit full compression of the indicator. The procedure for checking the proper tightening of bolt using DTI is shown in the figures below.

Fig: Inserting feeler gauge in space between indicator positions

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nut to indicate the relative position of the two. The mark shall be such that the same shall be visible for inspection upto 1 year after the date of installation. ii. Checks after first stage: After the first stage of tightening, following shall be checked: a) The steel members that make up the plies of the joint with HSFG bolts shall be checked for proper contact. b) 10 % bolts shall be checked with a separate calibrated wrench set at 75% of the proof 0

load for the bolt and any bolt turning by more than 15 during the same shall be rejected. If the loose bolts thus found are more than 5 but less than 1% of the total, another 10% of the bolts shall be checked. If the total loose bolts thus found exceed 1% of the total, the torque wrench shall be calibrated afresh and the entire lot shall be checked for tightness. iii. Second Stage Tightening: Then the bolts shall be turned by a further amount in proper sequence of tightening as specified below: Total nominal thickness “t” of parts to be connected (including all packing and washers), d = dia of bolt t < 2d 2d ≤ t < 6d 6d ≤ t ≤ 10d

Further rotation to be applied, during the second stage of tightening Degrees Part turns 60 90 120

1/6 1/4 1/3

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c) A fully tensioned bolt, opened out for any reason whatsoever, needs to be rejected and removed from the site of work. Along with the bolt, the nut, washer(s) and DTI(s) used on that bolt also need to be rejected and removed from the site of work. d) A bolt which has been snug tightened or partially tightened and then opened out will not be considered to have been retensioned and reuse of such bolts will be permissible in the same or different holes, as required. V.

Specifications of torque wrench: Except for works of minor nature where number of HSFG bolts to be installed is very less, only mechanical torque wrenches (pneumatic, hydraulic, electronic etc) shall be used for tightening of bolts. 27 For small quantum of work, manual torque wrenches may be used.

VI.

Calibration of torque wrench: Calibrated torque wrenches, accompanied with a certificate to the effect, shall be brought to site. Torque wrenches shall be calibrated periodically once in a year to an accuracy of ±10%. These shall be re-calibrated in case of any incidence involving the wrench during use resulting in heavy impact (such as fall, mishandling etc.) or if the joint is found to have been improperly tightened using the same. The procedure for calibration of torque wrench shall be as specified by the manufacturer.

VII.

Setting of torque in the Torque Wrench28: Torque shall be set in torque wrench as per recommendations of bolt fabricator. The same shall be within limits specified in table 5

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VIII.

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Other methods of Tensioning: There are other methods of tensioning, but only the two methods outlined above have been found to be suitable as per the field conditions prevailing on Indian Railways.

11. Economics of HSFG bolts: The HSFG bolts are direct replacements of rivets and with proper design, the number HSFG bolts in a joint/ splice shall be less than or equal to the number of rivets. At current prices, the cost of rivets and HSFG bolts are comparable to each other. Cost of HSFG bolts is likely to go down as the volume of work grows and multiple manufacturers are available. HSFG bolts bring other benefits to the railway, namely: I.

Reduced time of assembly/ erection.

II.

Reduced requirement of scaffolds.

III.

Less skilled manpower requirement.

IV.

Less rejections and easier supervision.

V.

Providing quality HSFG bolts is feasible as compared to other alternatives: welds in field are non feasible, whereas rivets are getting difficult to execute day by day.

12. Maintenance of HSFG bolts: I.

Anti-theft and Anti-sabotage measures: Where it is apprehended that theft/sabotage might take place, the bolt threads may be destroyed by applying welding tack to the bolt projection beyond the nut after final tightening and inspection. The tack shall not be more than 5 mm long and not more than 3 mm in size. It shall be especially ensured that too much heat is not imparted to the bolt as to alter its metallurgical properties.

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III.

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Use of HSFG bolts for repair/rehabilitation works: Where any girder component/joint is to be replaced, HSFG bolts shall be used as follows: (a) Complete joint shall have HSFG bolts. HSFG bolts cannot be used for replacement of isolated loose rivets. (b)Proper surface preparation shall be done and joint design shall be done based on design provisions as per para 7.12 of Steel Bridge Code. Particular care shall be taken regarding use of appropriate slip factor for the surface preparation done.

IV.

(i) Painting during initial installation: In case of HSFG bolts with “Direct Tension Indicating” device, the final coat in field applied on complete structure may be applied on HSFG bolts also. In case part turn method of tensioning is used without “Direct Tension Indicating” device, the HSFG bolts shall not be painted and the permanent location marks made on the bolts shall be visible after one year of installation.

(ii) Painting in service: HSFG bolts shall be painted as per normal painting schedules and painting methodologies as specified in the Indian Railways Bridge Manual for the girder as a whole.

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Provisions for DESIGN of HSFG Bolts (as per IRS Steel Bridge Code) IS:4000 provides for both bearing type joints which work more or less like rivets and friction type joints which act on friction between plies. Bearing type joints as defined in IS 4000 shall not be provided using HSFG bolts on bridges covered by IRS Steel Bridge Code. Only friction type joints shall be provided using HSFG bolts for all structures covered under IRS Steel Bridge Code. 1. Plies: The plates/ members joined together through HSFG bolts are called plies. To join dissimilar members, suitable packing shall be provided if the difference in thickness is more than 1 mm. From maintenance considerations, too thin packing plates are not desirable. In design, no 30

additional factor need be considered for t he packing thickness.

2. Diameter of bolt: Normally, for structural design, 20 mm or 22 mm dia bolts shall be chosen. However, if the joints are to be made smaller and for better detailing 24 mm and larger diameter bolts can be used. The bracing can also be design with 20 mm/ 22 mm dia bolts. However, if the load is too less, such as in foot over bridges, smaller diameter bolts can be used. 3. Diameter of hole: The nominal diameter of hole shall be 1.5 mm more than the bolt diameter 31 i.e. for 20 mm dia HSFG bolt, the hole shall be 21.5 mm in diameter. If the HSFG bolts are being used in existing structures, the oversize holes may be permitted subject to maximum of 1.25 d or d + 4 mm, whichever is less. 4. Deduction for holes: The deduction for holes and for asymmetric connections to get the effective area of the members shall be done in a manner similar to the one adopted for the holes for rivets and other bolts, i.e. the gross area may be considered in compression and net

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Note: If it is not possible to make proper surface preparations as given in 1 and 2 above, the slip factor shall be established as per 3 above and the same shall be used for design. Otherwise, the rivets shall be replaced by other modes such as by appropriate close tolerance turned bolts as per IS 1364 and para 28.6 and 28.7 of IRS B1. The preparation of surface by removal of paint is not allowed for new construction. If interface has been painted inadvertently, the same shall be sand/grit blast cleaned and metallising shall be done, even if the surface was already metallised. 7. Design of joints subject to shear: Most of the bolts in girders such as those that connect the bracing, cross frames, flange angles with web etc are subject to pure shear loading only. The design of HSFG bolts for such applications shall be such as to ensure that the shear force applied 35

does not exceed :           

   The minimum bolt tension is as specified in table 3 of IS 4000 and factor of safety shall be 1.4 under normal loads. Where the effect of wind load has to be considered on the structure, this factor of safety may be reduced to 1.2, provided the connections are adequate when (i) wind forces are not considered, and (ii) wind load is not the primary loading for the purpose of 36

design.

In other words, the factor of safety shall be adopted as 1.4 or 1.2 as per load case in case of Railway girders, Road Over bridges and turn tables etc where wind load is not a primary

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in the direction of the minimum distance toward the edge of a ply shall not exceed exfy x t/ 37

1.4. (wheree is edge distance of bolt plus half the bolt diameter, in mm). These provisions are meant to prevent failure of the steel members joined together by the HSFG bolts.

10. Design of joints subject to pure tension: Normally the bolts in railway application are not subject to pure tension. However, if such joints are to be designed, the tension in the bolts shall be limited to the values given in table 2 of IS 4000. (Which are equal to 0.6 times the minimum 38

bolt tension specified in table 3 of IS 4000). In case the bolts are subject to tension in fatigue conditions, the minimum tensile force in the bolt shall not exceed 50% of the minimum bolt 39

tension values specified in table 3 of IS 4000. Table 2 of IS 4000 is reproduced at Annexure II.

11. Tension to be given in Bolts: All HSFG bolts shall be tightened by procedure given in para 10 to impart the minimum tension specified in table 3 of IS: 4000 given in para10.I.b). The torque corresponding to the bolt tension indicated shall be as specified by the manufacturer of torque wrench. 12. Fatigue design: The HSFG bolts are pre-tensioned and the level of this tension does not change much even when subjected to repetitive loads, so these need not be designed separately for 40

fatigue. The structural steel plies which are connected by the HSFG bolts shall be designed for fatigue, if these are subjected to fluctuating loads as given in IRS Steel Bridge code. The fatigue category of the steel members shall be as given in IRS Steel Bridge Code. It is worth mentioning here that the fatigue category of members connected by HSFG bolts is higher than that for the members connected by rivets. This is because the shank and hole edges, where stress

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Provision c/c spacing (Maximum) Adjacent rivets in tension/ compression c/c spacing (Maximum) Bolts lying in direction of stress tension/ compression c/c spacing (Maximum) Bolts lying in direction of stress compression

c/c spacing (Maximum) Staggered, gauge not exceeding 75 mm Maximum Length of Bolt

32 t or 300 mm whichever is lesser 16 t or 200 mm whichever is lesser 12 t or 200 mm whichever is lesser If load is transferred by butting in compression members, for a length equal to 1.5 times width, the spacing shall not exceed 4.5 d. 50 % more than the values given in clause 7.4.2 and 7.4.3 The grip including the plies, packings and packing washers shall not exceed 10 times the nominal bolt diameter.

Where d is diameter of hole t is thickness of thinner outside plate

Reference Bridge Code Clause 7.4.1 of IRS Steel Bridge Code Clause 7.4.2 of IRS Steel Bridge Code Clause 7.4.2 of IRS Steel Bridge Code

Clause 7.4.3 of IRS Steel Bridge Code Proposed correction slip to IRS Steel bridge Code.

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Annexure I Annexure D of IS 4000 (Reproduced)

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Annexure II Table2 of IS: 4000 (Reproduced)

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Annexure III FREQUENTLY ASKED QUESTIONS RDSO is being contacted by field/ design engineers with their queries ever since this new subject has been introduced. Some of the most common questions are given below: 

Is there an RDSO approved vendors list for HSFG bolts? This most popular query is causing considerable distress to the bolt manufacturer and bolt users

alike. The concerns of the engineers with regards to quality of HSFG bolts are genuine as the age-old rivets are being replaced by a new product. The matter of vendor list to be prepared by RDSO is being discussed regularly in various fora. The latest orders with RDSO are to circulate a list of known suppliers to facilitate the field engineers to contact the manufacturers. However, there is no approved list and even the list of known manufacturers, if circulated by RDSO, will also be advisory in nature and any bolt manufacturer can supply the HSFG bolts provided the bolts are as per relevant codal provisions for which inspection may be done by zonal r ailways themselves or entrusted to some t hird party. 

Which is better – class 10.9 bolt or cl ass 8.8 bolt? HSFG bolts of class 10.9 are stronger than those of class 8.8. It is clear that for the same loads, the

number of bolts of class 10.9 will be lower than those of class 8.8. The class 10.9 bolts will, therefore, be cheaper than class 8.8 bolts on overall basis. There are certain issues, however, which need to be considered before we conclude the matter. The class 10.9 bolt is tightened beyond 90% of the Ultimate Tensile Strength of the bolt. While this is efficient use of the material, it creates some problems during tightening operations. If the torque wrenches are faulty, or due to other reasons, overload is applied to

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connected. Mostly this is not a problem but for very thin plates or where marginal edge distance has been provided, there can be some problem. If class 10.9 bolt is used, the tightening shall be done for

the load specified for class 10.9 bolt, otherwise the joint will not work as friction grip type and there can be problems. If only nuts are required to be changed to a higher category, there is no problem as nuts of higher category are stronger than those of lower category. This change can be done without design checks and the tightening shall be done for the loads specified for class 8.8 bolts only. 

Can we take supply of galvanized HSFG bolts and nuts? The HSFG bolts/nuts prescribed for Indian Railways shall have phosphate coating as per IS 1367

(Part XII), as specified in clause 28.9.4 (v) and 28.9.5 (vi) of IRS B1. Supply of galvanized bolts/ nuts shall not be taken as the bolts are susceptible to Liquid Metal Assisted Cracking during the hot dip galvanizing procedure. Since the bolts are to be painted with the girders, the same corrosion protection measures adopted for the complete girder shall be sufficient for the bolts also. 

Are HSFG bolts mandatory to be used for Foot Over Bridges and cover shelters etc? A major advantage of HSFG bolts is that the connection is much better in fatigue and there is good

amount of saving in steel due to this higher fatigue category. For structures not subjected to fatigue loading, like Foot Over Bridges and Platform cover shelters etc, where fatigue design is not done, HSFG bolts may not be required. For such structures, welding and load bearing bolts may provide better options. It is definitely not mandatory to provide HS FG bolts for such structures. 

Is it important to calibrate the DTI washers? DTI washers are specially engineered load indicators. These are very important for ensuring

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Annexure IV DOs AND DON’Ts FOR CONSTRUCTION ENGINEERS

DOs: 

Do ensure that all bolts, washers and nuts are accompanied by manufacturer test

certificates and appropriate markings indicating that these bolts are as per relevant codes. 

Do metallise the surface which is to be connected by the HSFG bolts, but without painting.



Do ensure that all bolts, nuts and washers are coated with zinc phosphate, sealed with suitable

oil of rust-prevention type(Only DTIs may have other surface coatings as approved by the manufacturer). 

Do make sure that there is proper storage arrangement for the bolts, nuts and washers away

from moisture, rain, dust, dirt and sunlight. 

Do clean and lubricate the bolt and nut threads if these are dirty.



Do ensure that the nut moves freely on the bolt threads.



Do use only calibrated torque wr ench (Calibrated within last 1 year).



Do properly check the bolts after initial tightening and after second stage tightening.



Do ensure that protrusions of the DTI are towards the bolt head or towards the nut depending

on whether the DTI is provided under the head or nut of HSFG bolt. 

Do use tapered washers wherever required.



Do check the tightening procedure if bolt breaks during tightening operation. It obviously means

ANNEXURE V: QAP FOR HSFG BOLTS,NUTS AND WASHERS FOR INDIAN RAILWAYS . N . S PARAMETER

1

Chemical composition

E L B A R C O I L F P P A

B, N, W, @ DTI

METHOD

INSTRUMENT

Spectroscopy/ Wet Analysis/

Analytical instruments/ Spectroscope

SAMPLE SIZE/ ACCEPTANCE/ EXTENT OF REF. DOC CHECK

Minimum 1 No/ Nominal diameter or Min 1 per 10000 nos.

IS:1367-6 for B and N. IS:6649 for W, relevant code for DTI

D E M R Y O B F R E P

S

D E S S Y E B N T I W

-

Y B D E W LOCATION E I V E R

Rly

At NABL/ government approved lab.

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Independent Testing

REMARK

To be done independently

If Spectro-test is decisive then wet analysis not required

@ For DTI washers, codes like ASTM F959 and EN 14399-9 are available. DTI washers are required to undergo additional testing to verify that manufacturer claims about efficacy. Before accepting any type of DTI washer of a diameter, 3 nos. DTI washers shall be checked as per procedure given in para 28.9.6 (iii)of IRS B1. Only those DTI washers that satisfy the acceptance testing shall be further tested and brought to site if found satisfactory. 2 Across flat, Across corner, Hex. Height, washer dia, washer thickness, total 2.1 length under head, thread length, Shank length, shank diameter, Mid chamfer & end chamfer etc

Dimensions

B

Measurement

Vernier Callipers/ Screw gauge

Minimum 1 No/Nominal diameter or 1 per 100 nos.

Rly (10% IS:3757

S

samples )

-

At works

-

For balance 90% samples, IC to be verified

Legend: B: Bolt, N: Nut, W: Plain Washer, DTI: Direct Tension Indicator Washer; S: SUPPLIER; Rly: Zonal Railway; IC: Inspection certificate; TC: Test certificate. Wherever works don’t have facility for any test(s), the inspecting official may allow testing to be done in any other laboratory

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3.3

3.5

Wedge load test & Proof load test (Where the product size does not permit the tensile test)

Impact strength


B, N

B

METHOD

Tensile test

Impact test

INSTRUMENT

Universal/ tensile testing Machine

Impact testing machine


Minimum 1 No/Nominal diameter or 1 per 1000 nos./ 1 no. per heat treatment batch

Minimum 3 No/Nominal diameter (1 Set) or 9 Nos per 1000 nos, (3 sets) whichever is higher. Or 1 set of 3 nos. per heat treatment batch.

IS:1367-3 for B, IS:6623 for N.

IS:1367-3


S

S


-

-


Rly

Rly

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Independent Testing

REMARK

At works

Minimum 1 per 10000 nos to be got independently done at NABL/ government approved Lab

TC to be reviewed

At works

1 per 10000 nos to be got independently done at NABL/ government approved Lab

TC to be reviewed




METHOD

INSTRUMENT

4

4.1

4.2





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Independent Testing

REMARK

At works

-

IC to be reviewed for balance 90% samples

At works

1 per 10000 nos to be got independently done at NABL/ government approved Lab

IC to be reviewed for balance 90% samples

Metallurgical tests

Decarburization

Re tempering test^

B

B

Measurement of Decarburizatio n, partial/complet e

Hardness Test

Microscopic examination

Minimum 1 No/Nominal diameter or 1 per 1000 nos, or 1 no. per heat treatment batch

Hardness testing and tempering furnace

Minimum 1 No per Nominal diameter or 1 per 1000 nos, or 1 no. per heat treatment batch

Rly (10% IS:1367-3

S

samples )

-

Rly (10% IS:1367-3

S

samples )

-

^ Surface hardness of the bolts is one of the most important parameters which may affect their performance. In addition to the value of surface hardness, depth of bolt material affected during the tempering process is also important. For verifying this, the record of temperature during the tempering process shall also be reviewed. Continuous record of temperature during entire process of tempering shall be made available for the same. If there are doubts about the process, bolt shall be cut and microstructure of the cross-section shall be verified.


Guidelines for High Strength Friction Grip Bolts

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