Bridge Manual 1998-27-65.docx

CHAPTER - II ============ MAINTENANCE OF BRIDGES PART A - GENERAL ================ 201. Responsibility of the Engineering officials ------------------------------------------- 1. Permanent Way / Works Inspector: a. Foundations, flooring, substructures, bed blocks and protection wo...

CHAPTER - II ============ MAINTENANCE OF BRIDGES PART A - GENERAL ================ 201. Responsibility of the Engineering officials ------------------------------------------- 1. Permanent Way / Works Inspector: a. Foundations, flooring, substructures, bed blocks and protection works of all bridges. b. Superstructure of all arch, pipe, box, PSC slab and RCC slab bridges. c. Steel work of girder spans less than 12.2m clear. 2. Permanent Way Inspector: 3. Bridge Inspectors: a. The steel work of all the girder bridges with clear span of 12.2m and above b. Superstructure of all RCC, prestressed concrete and composite girder bridges and c. The bearings of all the above bridges. 202. Action to be taken after inspection of bridges ---------------------------------------------- 4. All repairs as and when required should be executed expeditiously. 5. The Divisional/Senior Divisional Engineer and his officials including the Assistant Engineer shall arrange to carry out maintenance of and repairs to a. Foundations, flooring, sub structures, protection works, bed blocks, track over bridges and the approaches including guard rails and other appurtenances, superstructure of all arch, pipe, RCC Box, and RCC slab bridges, PSC slab bridges and steel work of girder spans less than 12.2m clear. b. Marking of HFL, Danger level, foundation detail and other particulars. c. Clearing of waterway and encroachments. 6. The Divisional Engineer (Bridges) / Assistant Engineer (Bridges) and his officials shall be responsible for the painting, rivetting, welding and other repairs to the steel work of all girder bridges of clear span 12.2m and above, all prestressed concrete bridges (except slabs), composite girder bridges and RCC girders. They shall also be responsible for the maintenance of bearings and holding down bolts of all bridges. 203. Painting of Bridges ------------------- 7. The date of painting of steel work should be painted in white on the outside of the left girder of the first span. In the case of important girder bridges, the left girder at each end should bear the date of painting. 8. The highest flood level line should be painted distinctly by a 25mm broad white line along with the year of its occurrence, in figures 100mm deep as follows: a. For bridges upto 60 metres in length, on the downstream side of one abutment, b. For bridges over 60 metres in length, on each of the abutments on the down stream side or on the down stream side of the piers of the end spans, c. For buried type abutments, on the piers near the end spans. 9. At important bridges, Flood level gauges should be provided on abutments or on piers of the end spans. The marking should be in 10. The direction of flow should be distinctly marked in white on an abutment or pier. 11. Plaques showing particulars of foundations should be fixed over every abutment and pier in accordance with instructions contained in Annexure 11/7. 12. Name boards at important bridges should be fixed at either approach at a distance of about 15 metres from the abutment indicating the name of the river and the number and length of spans. 8. At all Canal crossings, the Full Supply Level should be marked distinctly in the same way as the H.F.L. line for other bridges. 9. Danger level should be distinctly marked in red in all the bridges as stipulated in para 703. PART B MAINTENANCE OF FOUNDATIONS, ================================== 204. Maintenance of foundations -------------------------- 13. Shallow foundations a. A bridge foundation having less then 2M depth below bed level in case of arch bridges and 1.2M depth below bed level in case of other bridges is termed as shallow foundation. b. Bridges with shallow foundations in sandy soils or soils likely to scour should be protected by stone, brick on edge or CC flooring with drop walls and/or curtain walls to protect foundation from scour (Annexure 2/2). This method is generally suitable in cases where the velocity of flow does not exceed 1.5 metre per second and afflux is negligible. The top level of the flooring, drop and curtain walls should be kept at the normal bed level of the stream or slightly lower to allow for c. Whenever heavy scour is noticed on the downstream of the drop walls, scour hole should be filled with boulders or wire crate filled with boulders. 14. Deep foundations : a. A foundation which is deep enough, having required grip length below maximum scour level is termed as deep foundation. Normally no protection is required for such foundations. b. The river bed between piers should not generally be pitched, as the pitching stones if washed away, may lead to excessive scour down stream, resulting in damage to piers. c. If warranted by actual conditions, piers and abutments on these bridges can be protected individually by pitching stones around them. Depending upon the velocity of the current under the bridge, proper sized stones or stones filled wire crates can be dumped below low water level. The boulders should be of proper size which could be handled manually but could not be carried away by water current. The pitching will be best done during dry season or when stream is at low water level. d. In very severe cases of scour, piles are driven concentric to the foundation with boulders dumped in-between. Sausage crates containing boulders may also be placed in the scoured portion around the piles. 205. Maintenance of Protective Works ------------------------------- 15. Meandering rivers during high floods may out flank and damage bridge and approaches. To control the same, following protective works are provided, singly or in combination. a. Guide bunds b) Marginal bunds c) Spurs/groynes 16. Pitching : 206. Maintenance of waterways ------------------------ 17. Obstructions in waterways should be cleared away on both sides of the line within railway limits for the full extent of the waterway. 18. Boundary pillars on each bank of a river or important waterway shall be erected so as to prevent and control encroachments. PART C MAINTENANCE OF SUBSTRUCTURE ================================== Abutments, piers, wing walls and return walls --------------------------------------------- 19. Weathering : 20. Leaching of mortar : 21. Leaning / Bulging of abutments, wing walls & return walls : a. To avoid build up of hydrostatic pressure following steps should be taken : i. Weep holes be provided at 1m interval in both horizontal and vertical directions if not already provided. The bottom most row of weep holes should be above low water level in case of flowing streams; 25 cm above bed level in other cases & above FSL in canal bridges. ii. Adequacy of existing weep holes be checked and if required, additional weep holes of proper size be provided. iii. Choked weep holes be cleaned and made functional. iv. The back fill material should be granular and should not contain expansive soil like black cotton soil etc. Proper filter layer be provided behind the masonry. The back fill material should be changed if so warranted. b. The excessive earth pressure can be taken care of by either providing masonry or cement concrete buttress. However, care should be taken that the reduction in water way, if any, does not adversely affect the parameters like afflux, clearances etc. c. For tackling undermining/scour and other rehabilitation problems para 204 and 513 may be referred to. 22. Cracks in masonry / concrete : a. Vertical cracks : b. Horizontal cracks : Maintenance of arches --------------------- 23. Defects in arch barrel proper : i. Extension of cracks from substructure to arch barrel : As arch is resting on substructure, the cracks in substructure due to differential settlement etc. may extend through the arch barrel also and may appear as longitudinal cracks (cracks parallel to the direction of traffic) (Annexure 2/4). These cracks are to be grouted with cement / epoxy mortar and tell tale provided to observe further propagation if any. The reasons of unequal settlement should be identified and remedial measures taken. ii. Transverse or diagonal cracks in arch barrel (intrados) (Annexure 2/5) iii. Crushing of masonry : Probable Cause Remedial Action ------------------------------ a. Leaching of mortar in Raking out the mortar and the joints. deep pointing / grouting b. Weathering of masonry Pointing together with grouting c. Excessive loading Reducing the imposed load or strengthening the arch d. Inadequate cushion Providing the minimum cushion over arch. or strengthen the arch. iv. Loosening of keystone and voussoirs : v. Longitudinal cracks in arch away from spandrel wall: 24. Defects associated with spandrel wall : +-----------------------+-----------------------+-----------------------+ | | i. ii. | i. ii. | +-----------------------+-----------------------+-----------------------+ | | i. ii. | i. ii. iii. | +-----------------------+-----------------------+-----------------------+ | | i. ii. iii. | i. ii. iii. iv. | +-----------------------+-----------------------+-----------------------+ +-----------------------+-----------------------+-----------------------+ | | i. ii. iii. | i. ii. iii. | | | | | | | | | | | | | | | i. ii. iii. | i. ii. | +=======================+=======================+=======================+ | | | | +-----------------------+-----------------------+-----------------------+ | | | | +-----------------------+-----------------------+-----------------------+ | | | | +-----------------------+-----------------------+-----------------------+ | | | | +-----------------------+-----------------------+-----------------------+ | | | | +-----------------------+-----------------------+-----------------------+ | | | | +-----------------------+-----------------------+-----------------------+ 25. Leaning of parapet wall : 26. General instructions for maintenance of arch bridges : a. Rail joints on the arch should be eliminated completely. In multiple span arches, these should be located over the haunches. b. Flat bottom sleepers should preferably be used over the arches. c. Clean ballast cushion should be ensured by periodical screening as necessary. It will be preferable to maintain minimum cushion over the arch by suitably regrading the track wherever feasible. d. For arch bridges on curves, it should be ensured that the track is centrally located. Where it has shifted towards the outside parapet over a course of time, it should be slewed back to the correct location to ensure equitable distribution of load. e. While carrying out repair works for existing arches, the filling should not be disturbed as far as possible, as the compacted fill over the arch relieves the arch ring of a portion of the superimposed load. f. If warranted by circumstances, whenever an arch bridge is opened for rehabilitation purposes, the extrados of the arch should be made water proof. A porous filling such as brick bats, ballast, etc. should then be used to cover the whole of the extrados to a depth of 300mm. The haunches over the piers should be filled with impervious material such as lean cement concrete with proper cross slopes leading to weep holes located at the top of the haunch filling. The earth filling over the porous material should be done in layers, properly consolidated by ramming. Black cotton soil should in no case be used for filling purpose. Details of common repair techniques ----------------------------------- Cement pressure grouting ------------------------ a. This technique is used i. When cracks are dormant ii. Cracks are active but cause of cracking has been determined and remedial action has been taken. iii. When honey combing is present in concrete structures. iv. When masonry is hollow. v. When deep leached mortar joints are present. b. Materials proportion and pressure : c. Equipment used : i. Air compressor with a capacity of 3 of 4 cum. per minute and with a pressure of 2 to 4 kg per sq. cm. ii. Grout injecting machine or grouting pump with inlet and outlet valves and pressure gauges. This can be power or hand driven. iii. An air tight, pressure mixer chamber, with stirrer for proper mixing of the grout and keeping it in proper colloidal suspension during grouting. iv. Flexible pressure hose pipes for transmitting grout from pressure chamber to ports embedded in the masonry. v. Drilling equipment, pneumatic or electric, for drilling of holes upto 25mm dia. vi. 12-20mm dia. G.I. pipes with couplers. d. Procedure for cement grouting : i. Holes are drilled in structure along cracks and in and around hollow spots. If there are several cracks, holes can be drilled in a staggered manner at 500 to 750mm spacing in both directions covering adequately the area proposed to be grouted. Holes spacing can be altered as per site conditions with approval of the Engineer. ii. G.I. pipe pieces (12 to 20mm dia x 200mm) with one end threaded are fixed in the holes with rich cement mortar. iii. All the cracks and annular space around G.I. pipes are sealed with rich cement, mortar. All the cracks are cut open to a \'V\' shaped groove, cleaned & sealed with rich cement mortar. iv. All the Grout holes should be sluiced with water using the same equipment a day before grouting as per following sequence; so as to saturate the masonry. v. The same sequence as described above is adopted for injecting the cement grout also. The grout is kept fully stirred / agitated under pressure throughout the grouting. The grouting is carried out till refusal and / or till grout starts flowing from the adjacent hole. A proper record of the quantity of grout injected into every hole should be maintained. vi. After grouting, curing should be done for 14 days. vii. Tell tales are provided for checking the effectiveness of grouting. viii. Only such quantities of material for preparing grout should be used, as can be used within 15 minutes of its mixing. ix. Grouting equipment must be cleaned thoroughly after use. 28. Epoxy grouting -------------- a. Composition : The epoxy grout consists of an epoxy resin and a hardener which react chemically when mixed. Epoxy resins are thermosetting and by suitably proportioning of the mix of resin, hardener and thinner (if necessary), the viscosity of the mix can be varied to suit all types of conditions. Grouting of wide cracks require large quantity of grout material. In such cases suitable fillers e.g. dry silicon flour etc. can be added based on manufacturer\'s recommendations. b. Specification : Considering the width, depth and extent of cracks and other relevant details, the viscosity of the resin hardener mix, their c. Test certificates : The supplier should produce test certificates for Pot life test, strength test and shear test from approved test houses. d. Equipments required : i. Pneumatic or electric hole drilling equipment. ii. Pressure injection equipment of standard make with necessary control valves and gauges, etc. iii. Air compressor of capacity 3 to 4 cum/min. and pressure of 10 kg/cm2. iv. Polythene or metal pipe pieces 6-9mm dia. v. Polythene/plastic containers for mixing the epoxy formulation. vi. A portable generator. e. Procedure for epoxy grouting (Annexure 2/8) i. The area to be grouted should be dry and free from oil, grease, dust and all loose and unsound materials. ii. All cracks should be cut open to a \'V\' groove about 10mm deep by mechanical or manual means. Loose material should be removed by using compressed air and groove fully sealed using epoxy mortar at least one day in advance. iii. Nails are driven into the cracks at 15 cm to 50cm intervals along the crack. iv. Holes of 7 - 10 mm dia should be drilled along the cracks and copper or aluminium or polythene pipe pieces of 6 - 9 mm dia fixed as grout nipples around the nails and allowed to rest on them. v. Epoxy formulation is injected from the bottom most pipe, keeping all other pipes, except the adjacent ones, blocked by wooden plugs. The injection is done using suitable nozzles connected vi. Due to restriction of pot life, it is advisable to mix only small quantities of epoxy at a time. All proportioning should be by weight and mixing should be thorough. vii. Low viscosity resins may be adopted for thin cracks. viii. A record of materials consumed should be maintained. f. Precautions while handling epoxy resins. i. Manufacturer\'s detailed instructions should be followed for safe handling and processing. ii. Direct skin contact should be avoided and hand gloves (rubber) and protective goggles should be used. iii. The grease gun syringe should be washed with acetone immediately after use. 29. Shot creting / Guniting ----------------------- a. Shotcrete is mortar or concrete conveyed through a hose and pneumatically impinged at high velocity on to the surface to be treated. The force of the jet impinging on the surface compacts the material. Generally a relatively dry mixture is used so that it supports itself without sagging or sloughing even for vertical and overhead applications. This process is also known as Guniting. b. Shotcrete or gunite is suitable for repairing spalled concrete surface as well as for strengthening weathered stone or brick masonry. For most applications mortar applied by the dry process (guniting) is adequate. With concrete (shotcrete) the wet process is adopted. In both the cases reinforcement in the form of wire 3mm dia, wire fabric or steel bars upto 16mm dia may be used, as necessary. c. Equipment required (Annexure 2/9) i. Guniting machine complying requirements given in IS : 6433. ii. Air Compressor with a capacity of 10 cum/per minute and which can develop a pressure of upto 7 kg/cm^2^. iii. Placing nozzle with hose. d. Specification of materials used : i. Ordinary Portland cement to IS : 269. (Other special cements can be used for special applications requiring higher strength or early setting) ii. Sand conforming to IS : 383 and graded evenly from fine to coarse as per Zone II and III with a nominal max. size of 6mm. iii. Coarse aggregate, when used, should conform to IS : 383, with a maximum nominal size of 10 to 12.5 mm. iv. water conforming to IS : 456. v. Admixture as recommended. vi. Reinforcing bars, as per IS : 432 or welded wire fabric conforming to IS : 1566 may be used as required. vii. Water cement ratio 0.35 to 0.50 by weight. e. Preparation of surface : All weathered or deteriorated material should be removed until the surface exposed is sound and properly shaped to receive the gunite (Shotcrete). The surface should be cleaned of all loose and foreign materials with an air/water jet. If the joint mortar is weak, the joint should be raked to about 10mm depth and all loose, dry mortar scraped out. Exposed reinforcement should be cleaned free of rust, scale etc. and given a coat of neat cement or any other anti-corrosive material. Porous surface should be kept damp for several hours before guniting. f. Form work : The forms where required shall be plywood or other suitable material set true to line and dimension. They should be adequately braced and constructed so as to permit the escape of air and rebound during the guniting operation (particularly in the case of thick members). g. Reinforcement : Depending on the thickness and nature of the work; reinforcement may consist of either round bars, or welded wire fabric 3mm diameter. Sufficient clearance should be provided around the reinforcement. The minimum clearance between the reinforcement and form or other back up material may vary between 12mm for the mortar mix and wire fabric reinforcement to 50mm for the concrete mix and 16mm dia reinforcing bars. However, the minimum cover for reinforcement shall be as per IS : 456. The minimum wire mesh spacing should be 50 mm by 50 mm. Clear spacing between bars should be atleast 65 mm. h. Preparing the gunite : The cement and sand in specified proportion are premixed and placed in the feeding chamber; the same is then fed into the working chamber through a cone valve controlled from outside. The mixture, after passing through an agitator is then carried in suspension by compressed air through the delivery hose to the nozzle. The mixing time shall not be less than one minute. As the material passes through the nozzle body, it is hydrated with water introduced in the form of a fine needle spray. The amount of water added is adjusted so that the in-place gunite/shotcrete is adequately compacted and it neither sags nor shows excessive rebound. The mix used generally ranges from 1:3 to 1:4.5 and moisture content of the mixture before placing in the machine should be within 3 to 6%. i. Uniform air pressure is maintained at the nozzle outlet. For lengths of hose upto 30m, the air pressure is 3kg/cm2 or more. For longer lengths the pressure is increased by 0.35kg/cm2 for each additional 15m of hose and by 0.35kg/cm2 for each staging of 7.5m that the nozzle is raised above the gun. j. Placing : The total thickness of gunite required should be built up in a number of layers with an interval of about 4 hours. Each layer is built up by making several passes or loops of the nozzle over the working area. The distance of the nozzle from the work, usually between 0.5 and 1.5m, should be such as to give the best results. Particular care should be taken when gunning through and encasing reinforcing bars. (For walls, columns and beams, the application should begin at the bottom). In guniting slabs, the nozzle should be held at a slight angle so that the rebound is blown on to the completed portion. k. Rebound : The rebound is mortar or concrete which bounces off the surface during the application. Rebound should not be worked back into the construction and should be rejected. l. Before laying additional layer, the first layer should be allowed to take its initial set. Then all laitance, loose material and rebound should be removed. The surface should be tested with a hammer for drummy areas which should be carefully cut out and replaced with the succeeding layer. m. Curing : The surfaces should be kept continuously wet for at least 7 days. n. Shotcreting by the wet process requires special equipment and can be used for building up thick layer. For further details reference can be made to IS : 9012 \"Recommended Practice for shotcreting\'\'. PART D ====== AND PRESTRESSED CONCRETE BRIDGES ================================ 210. Periodical maintenance ---------------------- 30. The areas around bearings shall be kept free of ballast, debris, dust, oil / grease etc. 31. Drainage system shall be thoroughly cleaned and repaired as necessary before the onset of monsoon. 32. Protective surface coat, where provided, shall be maintained. 33. The superstructure and bearings shall be maintained as per the design requirements and any deficiencies/defects noticed during inspection shall be attended to. 211. Common defects and repair/strengthening techniques -------------------------------------------------- 34. For the repairs of following type of defects, techniques described in para 209 may be suitably adopted. a. Signs of honeycombing and/or hollow spots in concrete components and spalling. b. Dormant cracks c. Active cracks whose cause of cracking has been determined and remedial action has been taken. 35. Other Strengthening techniques : a. External prestressing of concrete girders both in longitudinal and vertical directions can be successfully adopted as a strengthening measure. Vertical prestressing may be adopted to prevent separation of deck slabs which are generally cast in situ over precast girders. Longitudinal prestressing may be adopted to strengthen the girder and to increase its flexural strength. Longitudinal prestressing may be resorted to in cases where girders are required to carry increased load or the existing prestressed cables have deteriorated. b. Established techniques such as external bonding of steel plates etc. can also be adopted for which specialist literature may be referred. PART E ====== 212. Loss of camber in steel girders ------------------------------- 36. Steel triangulated (open web) girders are provided with camber to compensate for deflection under load. Out of the total design camber, the part corresponding to dead load is called dead load camber. The balance is called live load camber which should be available as visible and measurable camber in the girder when not carrying load. 37. Loss of camber can be mainly attributed to : a. Overstressing of members beyond the elastic limit b. Overstressing of joint rivets c. Loose rivets 38. Rectification measures : a. If it is established that the loss of camber is due to 2 (a) above which can be due to running of heavier loads or heavy loss of section of bridge member due to corrosion, action should be taken to strengthen the girder with proper camber or replace the girder. b. In case the loss of camber is due to overstressing of joint rivets the joint should be redesigned and rivets and gusset plates replaced as required after providing the designed camber. c. All the loose rivets should be replaced by sound rivets and proper camber provided. 213. Cracks in steel works --------------------- 39. Whenever a crack is detected in the steel work, its cause should be established and further propagation, if any, monitored. As a first remedial step, a small hole of 7mm diameter should be drilled at the extremities of the crack to prevent its further propagation. 40. As a long term solution the cracked member may be strengthened by cover plate (s), adequately rivetted. If this is not feasible, the defective member may have to be taken out and repaired/replaced. 214. Strengthening of weak girders ----------------------------- 41. Such cases generally occur when loads heavier than those considered for design have to be carried. It is likely that the entire girder may not need replacement, but only certain components may need strengthening/replacement. All the strengthening works require, very careful check of design, and planning for execution. 42. The common methods of strengthening are : a. Replacement of weak rivets by larger diameter rivets. b. Replacement/strengthening of floor system, namely, stringers and cross girders. c. Addition of flange/web plates to plate girders : For this removal of the girder from the road and replacement by a relieving girder may be necessary. d. Strengthening of weak members of an open web girder : As the work is of complicated nature, panel points will have to be jacked upon trestles to designed camber levels, to eliminate dead load stresses and weaker members replaced with stronger ones by accurately match marking and match drilling of rivet holes. 43. If work of an extensive and repetitive nature is involved, it is preferable to take out one member (such as cross girder, rail bearer etc.) at a time and replace it by a spare member specially manufactured for the purpose. The member thus taken out can be satisfactorily repaired outside and used to replace the next defective member and so on. 215. Replacement of loose rivets --------------------------- 44. General : i. Slight slackness of rivet does not cause loss of rivet strength. ii. Renewal of slack rivets should be done only when the slack rivets are in groups or are bunched up. Individual scattered slack rivets need not be touched. iii. Rivet is to be considered finger loose when the looseness can be felt by mere touch, without tapping. Rivets should be considered hammer loose, when the looseness can be felt only with the aid of a hand hammer. iv. All rivet renewals in a bridge girder shall be done only with pneumatic rivetting. In exceptional cases and at locations where pneumatic tools cannot be employed, hand rivetting may be resorted to. 45. The following points should be kept in mind while carrying out the rivetting work. a. In pneumatic rivetting, the driving of the rivet, filling of the hole and formations of the head should be done by snap mounted pneumatic hammer by delivering quick hard blows on practically white b. The rivet shank should be about 1.5mm less than the diameter of the drilled hole. c. The length of the rivet shank may be worked out by the formula L = G + 1.5D + 1mm for every 4mm of grip or part there of for d. While rivetting a loose joint, not more than 10% rivets should be cut at a time. Besides, each rivet should be replaced immediately after cutting, with a turned bolt of adequate diameter and length and then only the next rivet should be cut. In 50% of the holes cut parallel drifts of correct diameter may be used; using turned bolts for the other 50%. e. It is preferable to drill a rivet out than to use a rivet burster as the latter cuts the rivet head in shear, imparting very heavy shock to the adjoining group of rivets. f. In a joint where only a few rivets are loose, the adjoining rivets are also rendered loose while bursting the loose rivets. In any case, after the loose rivets in a joint are replaced, it is very necessary that all the rivets in the assembly are rechecked for tightness. g. At locations where replacing rivets is difficult, turned bolts of appropriate diameter and length may be used. h. The rivet must be heated almost to a white heat and to a point when sparks are just beginning to fly off. The whole rivet must be brought to the same heat. The rivet should be driven and the snap removed within 20 seconds of the rivet leaving the fire. j. The rivet must be driven straight, while hot, keeping the hammer coaxial. The rivetter must have his staging at a height which enables him to put the whole weight of his body behind the hammer. This prevents it from bouncing. k. Rivets conforming to IRS specifications only should be used. l. Adequate air pressure of 5.6 to 7 kg/cm2 should be ensured for opening of the tools. m. In the case of long bridges, the air compressor may be centrally located at a suitable trolley refuge, with main pipe line running in both directions with suitable tappings. 46. The following guide-lines may be followed for replacement of loose rivets in plate girders. Renewal of slack rivets should be taken up for : i. All rivets which are hand loose or which have lost 50% of their head by corrosion. ii. All hammer loose rivets where corrosion has set in between the head and the plate. iii. In end stiffeners when the percentage of hammer loose rivets is \>30% iv. In flange splices when the number of hammer and hand loose rivets is 30% or more of the total rivets on any side of the splice location, all the rivets should be renewed. v. All hammer loose rivets at main angle to web connection upto 1/12 span from either support of the girder. vi. When loose rivets in end connections of lateral and cross bracings of plate girder spans require renewal, all the rivets in the end connections should be renewed. vii. Subject to the conditions in (i) and (ii) above, rivets, though hammer loose, need not be renewed under the following locations : a. In the lap or butt joints of trough flooring, b. Through angle or tee intermediate stiffeners on girders, c. At main angle to web connections except those covered in (v), d. In flange plates, e. In web splices. 215A. Maintenance of HSFG Bolts: -------------------------------- i. **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. ii. **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 so as to alter its metallurgical properties. Alternatively, proven bonding agent may be applied to the threads projecting beyond the nut to seize or lock the bolt in position **(ACS 27 dtd. 03.01.2014)** 216. Corrosion and its prevention ---------------------------- 47. Corrosion is deterioration of metal due to its interaction with the corroding environment. 48. When steel is exposed to the atmosphere, it combines chemically with the oxygen to form oxides. This is generally described, as rust. In addition, steel gets corroded by other harmful chemicals to which it may be exposed, such as acidic fumes and salt in sea spray etc. 49. Corrosion may take place in either of the following forms : i. Uniformly over large areas, referred to as \"Uniform corrosion\" or limited over a local area, referred to as \"local corrosion\". ii. Restricted to an extremely minute area, referred to as \"pitting\". 50. Prevention of corrosion : Corrosion may be prevented by any one of the following means : a. Protective coatings by painting (refer para 217). b. Metallising - a form of protection by spraying a metal either zinc or Aluminium (refer para 218). c. Use of epoxy based paints. 217. Protective Coatings by painting ------------------------------- 51. Correct surface preparation of the steel to receive the paint: This is the single most important factor in ensuring good performance, as the presence of rust under the paint film can cause its failure. Removal of rust, oil, grease and dirt is also necessary to ensure adequate adhesion of paint film to the surface. a. The minimum requirements of a surface prepared for painting are: i. It should be clean, dry and free from contaminants. ii. It should be rough enough to ensure adhesion of the paint film. However, it should not be so rough that the film cannot cover the surface peaks. b. Any one or a combination of the following methods (i to iv) for surface preparation may be used, where rust has appeared in many places and existing primary coat of paint has developed cracks, blistering, peeling, brittleness etc. i. Manual hand cleaning : The cleaning of surface is done with the use of emery paper, wire brushes, scrapers, etc. This is adopted for spot cleaning during normal maintenance to remove rust, scale or old coatings. ii. Cleaning with power driven tools : Oil and grease are first removed. Heavy scale and rust are then removed by hand tools. Residual rust and mill scales are removed by hammer or rotary action of hand held power driven tools. iii. Blast cleaning (sand or grit blasting) : It consists of cleaning the surface with the help of high velocity impact of abrasives (sand or grit) against the surface. It removes rust, mill scale (oxidisation) and old paints along with some of the base metals and creates a base for good adhesion. It is the most effective method of surface preparation. iv. Flame cleaning : The process consists of localised application of an oxy-acetylene flame on the steel surface. After the application of the flame the rust can be removed by wire brushes. Flame cleaning should not be done on plates with thickness 10mm or less as it may lead to permanent distortion of such plates. v. In the case of maintenance painting where only the finishing coat of paint shows signs of deterioration and the primary coat of paint is sufficiently in good condition adhering to the metal firmly and there are no signs of rust, the surface should be washed with lukewarm water containing 1 to 2% detergent to remove salt deposits and grime. After this, the surface is to be dried, lightly wire brushed and sand papered. Onthis prepared surface only the finishing coat of paint should be applied. vi. Temporary coatings : If, for any reason, painting can not immediately follow surface preparation, corrosion can be prevented for a short time by means of temporary coating of Linseed oil applied uniformly and thinly (one third litre on 10m area will be sufficient). Modern prefabrication primers which are easier to apply and give better protection are also available. 52. Choice of suitable paints : The following system of paints may be adopted for painting of Bridge girders : a. In areas where there is no severe corrosion OR  b. In areas where corrosion is SEVERE i) Priming Coat : (ACS 26 dtd. 28.08.2013) ------------------------ 53. Conditions for obtaining good painting : a. Painting should be done in dry and reasonably warm conditions. The relative humidity should not be above 90%. b. Dew frequently condenses on a structure during night and hence painting at night and in the early hours of morning should be avoided. c. Painting should be avoided during rainy season and in adverse weather conditions (dust storm, mist, fog, etc.) d. Control of paint film thickness : i. It is desirable to control and check the thickness of paint applied to a structure. The wet film thickness can be monitored by means of the wet film gauges from the rate of paint consumption at intervals during application. To provide a recognizable surface appearance and assist in rapid visual inspection during the course of the work, a reference patch or patches of required thickness should be painted on the structure. Measurements of Dry Film Thickness (DFT) should be done systematically over the whole structure and results assessed. Attention should be paid not only to the average DFT but also to uniformity of application. The normal thickness as also ii. Measurement of dry film thickness (DFT) : The following instruments may be used to measure the DFT. 54. Precautions to be taken during Bridge painting : a. Paints from approved manufacturers only should be used. b. Special care should be taken to shift sleepers on girders or rail bearers to clean the seating very thoroughly before applying the paint. d. While painting with IS: 13607, a little quantity of same paint of other shade shall be added to the paint while doing the first coat to distinguish it from the second coat. Similarly, in the case of aluminium paint a little blue paint can be added for1st coat. e. Paints should be used within the prescribed shelf life from the date of manufacture. The quantity of paint procured should be such that it is fully utilised before the period prescribed for its use. The shelf life of various paints used in the Railways are as follows: i. Paint Ready mixed Zinc Chrome Primer (IS : 104): 1Year ii. Paint to IS:13607 with colour/shade to be specified by Zonal Railway: 1 year iii. Paint aluminium: iv. Oil linseed boiled: 2 years v. Paint ready mixed Red Oxide Zinc Chrome (lS:2074): 1 year vi. Red Oxide Zinc Chromate Primer (IRS-P-31): 1 year. f. Brush shall not be less than 5cm in width and should have good flexible bristles. A new brush before use should be soaked in raw linseed oil for atleast 24 hours. The brushes shall be cleaned in linseed oil at the end of each day\'s work. g. Dust settled after scraping shall be cleaned before applying paint. h. When the paint is applied by brush, the brush shall be held at 45 to the surface and paint applied with several light vertical / lateral strokes turning the brush frequently and transferring the paint and covering the whole surface. After this, the brush shall be used crosswise for complete coverage and finally finished with vertical / lateral strokes to achieve uniform and even surface. j. Rags, waste cotton, cloth or similar articles should not be used for applying paint. k. The coat of paint applied shall be such that the prescribed dry film thickness is achieved by actual trial for the particular brand of paint. The applied coat of paint shall be uniform and free from brush marks, sags, blemishes, scattering, crawling, uneven thickness, holes, lap marks, lifting, peeling, staining, cracking, checking, scaling, holidays and allegatoring. l. Each coat of paint shall be left to dry till it sufficiently hardens m. The entire contents of a paint drum should be mixed thoroughly either by pouring a number of times or by mechanical mixing to get uniform consistency. The paint should not be allowed to settle down during painting by frequent stirring or mixing. Driers such as spirit or turpentine should not be used. Mixing of kerosene oil is strictly prohibited. n) The maximum time lag between successive operations as indicated below shall not be exceeded. i. Between surface preparation and the application of primer coat -24 hours ii. Between surface preparation and first finishing coat in the case of patch painting - 48 hours iii. Between the primer coat and the Ist finishing coat -7 days iv. Between the Ist finishing coat and the 2nd finishing coat - 7 days 55. Periodical through painting : intervals which may vary from six years in arid zones to one year in highly corrosive areas. The chief Engineer shall prescribe the periodicity of painting. Floor system of girders etc. where corrosion is heavy, may require painting more frequently. Their periodicity should be as specified by the chief Engineer. 56. Patch painting : a. When small areas of paint show pronounced deterioration, which require immediate remedy, it is not desirable to wait for the girder or the member as a whole becoming due for periodic painting. The affected areas must be patch painted. The usual locations which may require patch painting are : i. Some parts of the girders like the upper surface of top chord members, ii. The inside surface of bottom chord members, iii. top flanges of plate girders, iv. Deck systems of through or semi through span etc. b. The surfaces requiring patch painting should be scraped down to bare metal and the painting techniques followed on similar lines, as prescribed for painting to cases where the existing paint coats have deteriorated fully. There may be cases where the top coat only has failed, in which case the affected top coat should be wire brushed thoroughly and required number of finishing coats applied. Metallising & Epoxy based Paints -------------------------------- For locations where girders are exposed to corrosive environment i.e. flooring system of open web girders in all cases, girders in industrial, suburban or coastal areas etc., protective coating by way of metallising or by painting with epoxy based paints may be applied : Metallising ----------- In metallised protection base metal like zinc or aluminium is lost by the atmospheric action, while the base metal (steel) remains unaffected. Zinc or aluminium can be sprayed on the surface prepared by grit/sand blasting for giving such protection, known as metallising. i. Surface preparation : a. The surface of steel shall be free from oil, grease, bituminous materials or other foreign matter, and shall provide an adequate key for the sprayed metallic coating. This may be achieved by flame cleaning or by sand blasting. However, the abrasive once used for cleaning heavily contaminated surface should not be reused even though rescreened. b. Final cleaning is done by abrasives i.e. Chilled iron grit G.24, as defined in BS : 2451 or Washed salt free angular silica sand of mesh size 12 to 30 with a minimum of 40% retained on a 20 mesh screen, as per following details : c. The final surface roughness achieved shall be comparable to roughness with a reference surface produced in accordance with Appendix A of IS : 5909 and shall provide an adequate key for subsequently sprayed metal. ii. Metallising process : a. The sprayed coating shall be applied as soon as possible after surface preparation. The wire method shall be used for this purpose, the diameter of the wire being 3 mm or 5 mm. The composition of the aluminium to be sprayed shall be preferably in accordance with BS : 1475, material 1-B (99.5%) aluminium otherwise as per IS : 739. b. Clean dry air at a pressure of not less than 4.218 kg per sq.cm. shall be used. The minimum thickness of metal coating applied shall be 115 microns and average thickness 150 microns. c. The specified thickness of coating shall be applied in multiple layers, not less than two. The surface after spraying shall be free from uncoated parts or lumps of loosely spattered metal. d. Atleast one layer of the coating must be applied within 4 hours of blasting and the surface must be finished to the specified thickness within 8 hours of blasting. iii. Inspection : a. The metal coating shall be checked for thickness by an approved magnetic thickness measuring gauge. b. The calibration of the gauge should be checked against a standard of similar thickness within an accuracy of 10 per cent. iv. Finishing coat of painting : a. After the metallising, any oil, grease etc. should be removed by thorough wash with a suitable thinner and allowed to dry for 15 minutes. The painting may be applied by brush or by spray. The first coat shall be wash primer to SSPCPT - 3 53T or Etch primer to IS : 5666. b. The second coat shall be zinc chromate primer to IS : 104. The zinc chrome should confirm to type 2 of IS : 51. The 3rd and 4th coats shall be aluminium paint to IS : 2339. v. Maintenance painting of metallised girders : a. The need for periodical repainting and the method to be followed will depend on the condition of the existing paint. In most cases complete removal of existing paint film may not be necessary. b. The surface is cleaned of all oil, dirt and other foreign material. If the existing top coats of aluminium paint are found to be in good condition, it will be sufficient to apply one additional coat of the same paint, once in 5 years or at such closer intervals as specified. c. However, if the existing paint is found flaked or damaged, it should be removed completely by wire brushing without the use of scrapers or chipping tools. In case the original coat of zinc chromate primer is also damaged in patches, such patches should be painted with fresh zinc chromate primer before applying the finishing coat of aluminium. d. In the event of any localised damage to the metallised coating of aluminium, as evidenced by traces of rust, the affected portion should be thoroughly cleaned of all rust before the priming and top coats of paints are applied. Rust streaks caused by droppings from the track or by contact with hook bolt lips should not be mistaken for corrosion. vi. Precautions to be taken while inspecting metallised girders : The use of testing hammers for rivet testing, or any other operation shall not be resorted to since these can damage the metallised coating. Any looseness of the rivets in bracings etc. may be detected from visible signs such as the appearance of rust under the rivet head. Epoxy based Paints ------------------ i. Surface Preparation : a. Remove oil/grease from the metal surface by using petroleum hydrocarbon solvent to IS : 1745. b. Prepare the surface by sand or grit blasting to Sa 2½ to IS : 9954 i.e. near white metallic surface. ii. Painting : a. Primer coat : b. Apply by brush / airless spray two coats of epoxy zinc phosphate primer to RDSO specification No. M & C /PCN-102/86 to 60 microns minimum dry film thickness (DFT) giving sufficient time gap between two coats to enable first coat of primer to hard dry. b. Intermediate coat : Apply by brush/airless spray-one coat of epoxy micaceous iron oxide to RDSO specification No. M & C /PCN- 103/86 to 100 microns minimum DFT and allow it to hard dry. c. Finishing coat : Apply by brush/airless spray two coats of polyurethane aluminium finishing to RDSO Specification No. M & C /PCN-110/88 for coastal locations or polyurethane red oxide (red oxide to ISC 446 as per IS : 5) to RDSO Specification No. M&C/PCN-109/88 for other locations to 40 microns minimum DFT giving sufficient time gap between two coats to enable the first coat to hard dry. The finishing coats to be applied in shop and touched after erection, if necessary. 219. Maintenance of welded girders ----------------------------- 59. Propagation of cracks in welded girders : a. Fatigue cracks develop in steel girders during service due to repeated loading and their magnitude depends on the magnitude of stress variation, frequency of stress application, type of connections, quality of fabrication and age of steel. Welds are more sensitive to the repeated stresses and once crack starts it can grow fast and seriously reduce the strength of the member. b. The location, length, orientation of cracks etc. should be marked distinctly with paint for easy identification, reference and subsequent monitoring of crack propagation. c. Each crack should be examined in detail with magnifying glass. Non destructive inspection methods like dye penetration test, ultrasonic test etc. as found necessary may be adopted. d. If identical locations exist elsewhere in the girder, they should also be closely examined. e. Significance and severity of crack should be studied on the load carrying capacity of the girder. f. Repair or retrofit scheme should be prepared after fully investigating the cause of the crack. 60. Repair of cracks : a. The method of repair of crack should be decided based on the location and severity of the crack. b. If the crack is propagating in a direction perpendicular to the stress in member, holes 20 or 22 mm dia may be drilled at crack ends to arrest the crack propagation. The edge of holes should be placed at visible ends of the crack. After holes are drilled it should be checked that crack tips have been removed and turned bolts of 20 or 22 mm dia as the case may be should be provided in the holes and fully tightened. Any reduction in strength of girder due to the crack and drill of holes should be given due consideration. c. Permanent measures may consist of the cracked member being retrofitted with rivetted or bolted splice or where feasible the entire member may be replaced. d. Field welding should not be undertaken for repair of cracks, unless they are of a minor significance. The repair should be done by trained welders and the repaired portions examined visually and/or by non destructive testing. PART F ------ The following action should be taken for maintenance of composite girders ------------------------------------------------------------------------- a. The welded steel portion of the composite girder should be maintained as per the procedure detailed in paras 217, 218 and 219. b. If separation of the concrete deck slab from the steel girder is noticed, the location and length should be marked distinctly with paint for easy identification. Repair and retrofit scheme should be prepared after fully investigating the cause of the problem. Epoxy grouting may be done to bind the deck slab and the girder where the defect is noticed and the girder should be kept under close observation. If the epoxy grouting is not found effective, vertical prestressing or strapping may be necessary for which holes should be drilled in the deck slab near the girder in the affected location and vertical prestressing/ strapping provided. c. The drainage system of the deck slab should be thoroughly cleaned and repaired as necessary before the on set of monsoon. d. Wearing coat where provided, should be maintained. e. Any deficiencies / defects noticed during inspection should be attended to promptly. PART G MAINTENANCE OF BED BLOCKS -------------------------------- 221. **The various defects and their remedies are outlined below** a. Improper seating of bearings: Due to uneven contact area, gaps exist between bed block and base plate. Cracks even develop due to improper seating of bearing. b. Shaken bed blocks : The bed blocks start loosening if they are of isolated type and a gap develops between surface of bed blocks and surrounding masonry. In such cases the remedy is grouting with cement mortar ensuring adequate curing and allowing sufficient time for the mortar to set. If bed block is shaken, the same should be inspected under traffic for visible movements and only then it should be confirmed as a shaken bed block. Action may be taken to either encase the bed block or replace it by through bed blocks. Precast bed blocks can be cast and bonded with epoxy resin mortar. (For details para 514.3 may be referred. c. Cracking and crushing of masonry : In these cases the most effective remedy would be to replace the bed blocks with an insitu, RCC, through bed block and attending to the cracks in the substructure. PART H MAINTENANCE OF BEARINGS ------------------------------ 222. **Bearings** 61. Types of bearings : The bearing transfers the forces coming from the superstructure to the substructure. It also allows for necessary movements in the superstructure which are caused by temperature variations. The following types of bearings are generally used. a. Sliding bearing permitting rotation and translation (Annexure 2/10) b. Rocker and Roller bearing (Annexure 2/11), with or without oil bath, permitting rotation and translation respectively. Oil bath bearings are generally provided for new girders of spans above 76.2m and for other open web girders, whether new or existing, in case it is considered difficult to lift the girders for periodic greasing. c. Elastomeric bearings (Annexure 2/12) permitting rotation and translation d. P.T.F.E. Bearings (Annexure 2/12) permitting rotation and translation 62. Maintenance of sliding and roller & rocker bearings : a. All bearings should be generally cleaned and greased once in three years. b. In the case of sliding bearings, the girder is lifted a little over 6mm and the bearing surfaces cleaned with kerosene oil and a mixture of black oil. Grease and graphite in a working proportion may be applied on bearing surfaces and the girder lowered. Jacking beams may be inserted wherever necessary. c. The roller and rockers are lifted from their position (by adequate slinging). The bearings are scraped, polished with zero grade sand paper and grease graphite in sufficient quantity applied evenly over the bearings, rockers and rollers before the bearings are lowered. The knuckle pins of both the free and fixed and should also be greased. While lifting fixed ends, the space between girders (in case of piers), or between the girder and the ballast wall (in case of abutment) at the free ends should be jammed with wedges to prevent longitudinal movement of the girders. d. Phosphor bronze bearings need not be greased as they are corrosion resistant and retain the smooth surface. e. The tooth bar of the roller assembly should be placed vertically at mean temperature. It will be better to indicate in the completion drawings of bridge stress sheet, the maximum expansion, and range of temperature for which the bearing is designed, so that the slant at the time of greasing can be decided depending on the temperature obtaining at the time of greasing. f. In the case of roller bearings with oil bath, dust covers should invariably be provided to keep the oil free from dirt. Wherever oil bath bearings are provided, inspection of the bearings, after removal of the casings to the extent necessary, should be carried out at least once in 5 years. Checking of oil level, draining out as necessary to detect and remove any water collected at the bottom and replenishing the oil, should be done annually. The oil in oil bath 63. Elastomeric bearings : a. Elastomeric bearings are made of natural or synthetic rubber of shore hardness of approximately 50 to 70. They are very stiff in resisting volume change but are very flexible when subjected to shear or pure uniaxial tension. They are generally reinforced with steel plates in alternate layers to reduce bulging. When used with a steel or concrete girder these permit moderate longitudinal movements and small rotations at the ends. b. These bearings require periodic cleaning. They may require replacement in service depending on the condition and usage. c. Whenever problems such as excessive bulging, tearing, off- loading, vibrations etc. are noticed, suitable action for repair/rectification shall be taken. If repair/ rectification is not d. If results of inspection are not conclusive to warrant replacement of bearings but doubts arise regarding performance of bearings, \'two representative bearings shall be taken dut from service and tested. The result of tests shall be compared with coda1 provisions to take further decision. e. When replacing any Elastomeric Bearing, then all bearings in one line of support (in transverse direction to traffic) of a span to be 64. Teflon or P.T.F.E. bearings : a. The coefficient of friction between steel and PTFE is quite low. The mating surface which forms the upper component of the bearing is stainless steel with good surface finish. The PTFE can be unfilled or filled with glass fibre or other reinforcing material. Its bonding property is very poor. Hence it is preferable to locate the PTFE by confinement and fitting of half the PTFE thickness in recess in a metallic matrix. b. These are used either to provide rotation by sliding over cylindrical or spherical surfaces or to provide horizontal sliding movement over flat surface or a combination of both. Where there are large displacements accompanied with relatively small loadings, as in case of centrifugal loads, wind loads or seismic loads, PTFE sliding bearings are utilised. c. These bearings also require periodic cleaning of the bearing surface. The interface should be protected from dust. Lubricating the mating surface by silicon grease reduces the coefficient of friction and is desirable. PART I GENERAL PRECAUTIONS -------------------------- 223. **Precautions while carrying out maintenance works on bridges** 65. For such works, as testing and changing rivets and painting, the Inspector incharge will arrange for look-out men equipped with hand signal flags to be stationed on both sides and for the issue of caution orders to drivers. 66. The Inspector incharge of works must personally satisfy himself that no staging or plant, infringes standard moving dimensions. If this is not possible, the work should be done under block protection. 67. In the case of through bridges or road over bridges on electrified sections, work near the conductors carrying traction current should be done after obtaining traffic and power blocks and under responsible supervision. 68. Where a maintenance or repair operation affects track, such work must invariably be done in consultation with and in the presence of the Permanent Way Inspector. 224. Dismantling of arch bridges: ---------------------------- 1. In case of running lines, prior CRS sanction for methodology/safety precautions, drawings etc. shall be obtained for dismantling work of the arch bridge. 2. Arch is a structure, which transmits heavy horizontal thrust to abutments and piers. In case of abutments, this load is resisted by heavy section of abutment and soil fill behind it. At piers, in case of multi span arches, horizontal thrust due to dead load is balanced. If both spans are loaded, horizontal thrust due to live load also gets balanced, but, in case of only single span being loaded, pier has to bear unbalanced horizontal thrust. Piers are, therefore, designed to take up only unbalanced horizontal thrust which is quite less as compared to total thrust at abutment. 3. Whenever in multi span arches, if one span is dismantled, large unbalanced horizontal thrust comes on pier and there can be collapse of pier along with other spans. Following procedure, suitable for both single and multi span arches, can be followed to safely dismantle arch bridges: a. **Dismantling with explosives: -** Explosives can be used to bring down all spans of an arch bridge at one go. This will require cordoning off the area likely to be affected by the explosion and long time to remove the debris thereafter. This method can only be used if the arch is not near habitated area and experts can be engaged to take up such work. b. **Dismantling with machinery:** -Special type of machinery