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Bridge Bearings

Bridge Bearings. Bridge Bearings. It is the interface between two major components of bridge structure i.e. super structure and sub structure. Types of movement in the bridge superstructure. Thermal expansion and contraction Deformation under live load

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Bridge Bearings

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  1. Bridge Bearings

  2. Bridge Bearings It is the interface between two major components of bridge structure i.e. super structure and sub structure.

  3. Types of movement in the bridge superstructure • Thermal expansion and contraction • Deformation under live load • Longitudinal forces- tractive / breaking • Wind loads • Settlement of supports • Seismic forces • Creep and shrinkage of concrete

  4. Functions of bearing: • Load transmission • Transfers the forces coming from the super-structures to substructure • Permit rotary or rocking movement caused by deflection of super structure. • Allow horizontal movement of super structure due to thermal expansion or contraction. • Bears part of the longitudinal force due to train load • Restrict lateral movement of super structure

  5. Bridge Bearing Accommodation of Translational movement of Superstructure- It is facilitated by any one or combination of the following mode of action by bearings- • By sliding action • By rolling action • By shearing strain

  6. Bridge Bearings Accommodation of Rotational movement of Superstructure- It is facilitated by any one or combination of the following mode of action by bearings- • By rocking/hinge action • By differential compression (as in elastomeric pads)

  7. SELECTION OF BEARINGS It isbasedon following factors • 1. Functional requirement • Vertical Load • Longitudinal Load • Maximum Longitudinal movement permitted • Maximum Rotation Permitted

  8. SELECTION OF BEARINGS • 2. Expected life – • Life of Bearing shall be the compatible with life of bridge • 3. Maintenance efforts- • Lifecycle maintenance effort on Bearings should be minimum • 4. Cost of Bearing- • For this lifecycle cost of bearing is considered & not the initial cost of Bearing.

  9. SELECTION OF BEARINGS • 5. Other factors • Overall height of the bearing assembly • Performance of bearing under seismic loads.

  10. TYPES OF BEARINGS ON RLY BRIDGES • Sliding steel plate plain bearing • Sliding steel plate articulated bearing • Centralised Articulated Bearing • Phosphor Bronze sliding Bearing • Roller & Rocker bearing

  11. TYPES OF BEARINGS ON RLY BRIDGES • Roller & Rocker oil Bath bearing • Elastomeric Bearing • POT-PTFE Bearing • Spherical Bearing • Pendulum Bearing • Shock Transmission Units

  12. SLIDING BEARINGS

  13. Co-eff of Friction for SLIDING BEARINGS Co-efficient of friction for different sliding surfaces are-

  14. C&G (cleaning & Greasing) of sliding Bearing • All bearings (Except POT-PTFE) shall be generally cleaned and greased once in three years. • In case LWR is continued over the bridge, C&G frequency shall be reduced to two years.

  15. C&G of sliding Bearing • In case of sliding bearing, the girder shall be lifted by not more than 6-8mm. Bearing surface shall be cleaned with K Oil and a mixture of black oil. • Approx 15-20 minutes are required to complete C&G of one end. • Grease and Graphite in working proportion shall be mixed and applied on the bearing surface and girder lowered.

  16. Equipments for C&G Equipments required for greasing of sliding bearings : • Jacks (appropriate capacity) 2 nos + 1 standby • Hard wooden packing (below and above jack) • Grease graphite grade 3 conforming to IS 508 • Kerosene and/or released black oil for cleaning • 6 mm thick steel scrapers • Mortar pan • Cotton waste.

  17. Lifting of 9.15 m girder for C&G

  18. Lifting of 12.2/18.3 & 24.4m span girders

  19. Lifting of Steel girders by Jacking Bracket

  20. Site Photograph of Jacking Bracket on Plate Girders

  21. Lifting Arrangement of Open Web Girder

  22. Precautions during C&G Work • To be done after duly informing P-Way, OHE departments • P Way staff shall preferably be available during C&G. • Proper protection of site as per IRPWM provisions shall be ensured and sufficient no. of look out man shall be deputed

  23. Precautions during C&G Work • Girder shall not be lifted excessively • (not more than 6-8 mm) • Properly Tested jacks shall be used for lifting of girder and spare jacks shall also be kept as standby • Girder shall be lifted from the permitted locations as prescribed. C&G of sliding bearing is carried out under suitable caution order.

  24. Items to be checked during C&G of Bearings During C&G following items must be checked – • Any crack/Brekage in Guide strips and Location strips • Holding down bolts loose or not fully driven • Corrosion in Holding down bolts • shaking of Bed Blocks • Cracks in Bed Blocks

  25. Items to be checked during C&G of Bearings During C&G following items must be checked • Sinking of bed plates into bed block • Crack in weld/ flange in girder near the bearing • Corrosion in bearing/ bed plate • Ballast/other debris near the bearing area (to be cleaned during C&G)

  26. Lifting of Track on Bridge • During repetitive tamping, level of track goes up as compared to level at bridge portion. • To correct the LL of track, bridge girder has to be lifted. • This is done by insertion of steel stool

  27. Lifting of steel girder with Stool

  28. Rectification for sunken Bed Plate • Thoroughly investigate the reason for sinking of bed plate and take corrective measures • Temporary support the girder on wooden blocks and take out the bottom plate. • Repair the top of damaged bed block with epoxy/polymer concrete • Use a new bed plate of higher plan area so as to distribute the load to a larger area of bed block

  29. Phosphor Bronze Bearing

  30. Phosphor Bronze Bearing • Phosphor Bronze bearing need not be greased as they are corrosion resistant and retain smooth surface. • However, area around the bearing should be regularly cleaned for proper functioning of bearing.

  31. ROLLER Rocker BEARING

  32. OIL BATH BEARING

  33. C&G of Roller & Rocker Bearing • Rollers and rockers are lifted from their position by adequate slinging. • Roller Bearings are scraped and polished with zero grade sand paper. • Grease graphite of sufficient quantity shall be applied evenly over the bearings, rockers and rollers to keep their surfaces smooth and bearing lowered.

  34. C&G of Roller & Rocker Bearing • Knuckle pins of both free and fixed ends shall also be greased. • While lifting the fixed end for greasing of knuckle, space between girders or between girder & ballast wall shall be jammed with wedges to prevent longitudinal movement of the girder. • Traffic block shall invariably be taken for greasing of these bearings.

  35. C&G of Roller & Rocker Bearing • Traffic block of approx 40-50 minutes are required for greasing of roller end and approx 25-30 minutes is required for greasing of rocker end. • C&G of roller and rocker bearing shall preferably be carried out in presence of ABE.

  36. C&G of Roller & Rocker Bearing • Roller & Rocker bearing should be free of corrosion and debris. • Tooth of roller bearing should be vertical at mean temperature. • For deciding the slant of teeth at greasing temperature, completion drawing should be referred which indicates the maximum expansion and temperature range for which bearing has been designed.

  37. C&G of Roller & Rocker Bearing • In case of oil bath bearing, dust covers shall be invariably provided to keep the oil free from dirt. • Oil of oil bath bearing- • Level of oil shall be checked every year and recouped • Oil shall be completely replaced once in five years.

  38. Items to be observed during C&G • Flattening of rollers • Cracks in rollers • Corrosion in rollers • Seizure of rollers • Problems in holding down bolts and bed plates

  39. ELASTOMERIC BEARING

  40. ELASTOMERIC BEARINGS Advantages:- • Minimum /Nil maintenance- as no moving parts • Installation is easy • Permits movement in all directions • Occupies small space • Serves as a shock absorber due to anti-vibrations (Damping) properties of elastomer • Transfer of longitudinal forces to Bridge Approaches efficiently

  41. c l c laminate b c

  42. SHEAR/ TRANSLATION ACTION

  43. ROTATION/ BENDING ACTION

  44. ACTION UNDER VERTICAL LOAD • Vertical load gets converted to shear in the elastomer/ laminate interface

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