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Girder launching and Re g irdering

Girder launching and Re g irdering. Launching: Introduction. Launching : Placement of Super structure on Sub-structure

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Girder launching and Re g irdering

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  1. Girder launching and Re girdering

  2. Launching: Introduction • Launching : Placement of Super structure on Sub-structure Undertaken for Construction of new line or doubling hence time of construction is not very tight. unlike in “Regirdering”, which is undertaken in open line under very tight time schedules.

  3. Regirdering: introduction • Replacement of the Old girder with New Girder • Additional features than Launching • Work to be done in traffic block normally • Girder to be fully ready before launching • Additional activity of Removal of existing Girder • Issues of change in the Rail Level • Issues of Safety of Traffic on adjacent Line(s)

  4. Preliminaries • Transportation of girders to site: • Span upto 12.2 m assembled in workshop and Transported to site by BFR • Longer plate girder spans transported in pieces and assembled at site • Can be transported over trailers also • Fabrication / casting of Span: Girders are assembled/ cast on Bridge approach or in situ.

  5. Scheme • The “Brain” of the entire exercise • It Decides • Success or failure of the scheme • Success or failure of the work • Time of the project • “Headache” to the supervisors at site

  6. Essential Feature of Scheme • Safety • Safe handling of span as well as men and equipment used. • Checking the erection stresses in each member of span during launching and if required temporary strengthening is to be provided. • Steel girders need careful handling to avoid damage to connections. • Concrete girders cannot be handled at any point. Depending on the design, only load may be applied at nominated locations only. • While providing temporary arrangements, proper care should be taken.

  7. Desirable Features of Launching Scheme

  8. Features of Launching Scheme • Speed • Completion of the work as per laid down time frame of project. • Project should not get delayed on account of bridge construction.

  9. Features of Launching Scheme • Economy • Scheme selected shall preferably be with available equipment and supporting false work. • Quality of construction to be maintained as per laid down specification. • Bridge girders are very costly asset and difficult to repair during service. • For sake of economy, safety cannot be compromised.

  10. Selection of Suitable Method • Particulars of Bridges and Span • Length, width, height and weight of girder • Number and type of spans • Steel or concrete or composite • I section or BOX girder etc • Height and width of piers/abutments • Space available • Skew or square span

  11. Selection of Suitable Method • Site Conditions • Height of opening • Wet, dry or partly dry ground/river bed • Depth of water and velocity • Vulnerability of river to flash floods • Condition of approaches - high banks or cuttings • Access to site • Road, rail or water access

  12. Selection of Suitable Method • Other Conditions • Experience of the contractor • Experience of the supervisors • Availability of bridging equipment and materials • No of spans • Estimated cost • Erection of girders is sometimes as costly as the main bridge • Avoid complicated and extensive staging or auxiliary girders in erection work. • Simplicity avoids mistakes at site

  13. Design of a Scheme • Girders should be designed/ checked for erection and handling stresses. • Scheme shall ensure that the girder does not get hit/ damaged during erection • Design of temporary work/false work used in erection is very important • Adequate extra factor of safety shall be there • Shall cater to mistakes and minor accidents • Shall cater to the “actual site conditions” i.e. loose bolts, wear and tear etc

  14. Preliminary Arrangements Before Start of Work • Plan sequence of erection work • Move girder materials to site • Make yard arrangements on one bank or nearby station • Arrange plant and equipment required for launching along with spans • Testing all equipment • Arrange for supervision, skilled and unskilled staff • Provide camp facilities for labour force.

  15. Preliminary Arrangements Before Start of Work • Discuss scheme at site with the railway and contractor supervisors • Also discuss with the contractor’s artisans about the scheme • Visualize failures • Have “Plan B” ready • First Aid and Communication at site • Arrange consumable stores

  16. Schemes as per site conditions

  17. Site Condition #1

  18. Site condition #1: features • Plain terrain • Accessible by road • Medium to low height • No water in river in some period of the year • Easy site

  19. Site condition #1: options • In situ erection • Side Slewing • On CC crib • On trestles • By portal crane • Road crane

  20. In situ erection

  21. In situ erection • Space under the girder is occupied by formwork • Superstructure work starts after sub structure work is completed • Lowering of girder to proper position to be done

  22. In situ erection: All the space can be used

  23. In situ erection: All the space can be used

  24. In situ erection: Even in slightly difficult site

  25. With pre-cast concrete units • Pieces are cast in yard and transported to site • On scaffolds, all pieces are placed • Stressing is done • Site is occupied for minimum time • Quality is maintained • Speed of work is good

  26. Derrick

  27. Derrick for steel girders Derrick • A column properly founded and guyed • Has freedom of movement in only one direction: vertical • Difficult to maneuver girder too much in lateral directions Useful for • Relatively smaller spans • Lesser no of spans Launching by derrick

  28. Service span pulled over opening using Derrick

  29. PSC girder launching using derrick

  30. PSC girder launching using derrick

  31. Side slewing

  32. Side slewing • Mostly used for regirdering • For launching, Superstructure can be cast/ fabricated at approach, pulled in position and slewed in

  33. Slew – in slew – out method TRANSPORT NEW GIRDER IN RIVER BED TO THE SPAN LOCATION

  34. Slew – in slew – out method IN BLOCK WITHOUT BLOCK SHIFT THE STAGING TO NEXT SPAN REGIRDERING IS NOW COMPLETE

  35. Side Slewing With C C Crib

  36. Side Slewing With C C crib Support

  37. Cast/ fabricate at approach and side slew: manual method I II III GIRDER

  38. Launching of Girders by road Cranes • Movement • Crawler mounted • Tyre mounted • Boom • Hydraulic • Mechanical

  39. Crawler Mounted Mechanical Crane

  40. Tyre Mounted Hydraulic Crane

  41. Launching of Girders by Cranes • Choose adequate capacity crane depending on the total load, radius at which the load is to be handled • Choose well maintained cranes • Plan the site layout and movement of cranes • Have sufficient standby

  42. Well designed lifting girder

  43. Site Condition #2

  44. Site condition #2: features • Difficult terrain • Not accessible by road OR • Height is great • Water in river all round the year OR • Multiple lines having no space AND • Isolated work for one/ two spans and moderate span length • Very difficult site

  45. Site condition #2: options • Railways’ 140 T Crane • Girder on BFR • Girder at bridge approach • Use of rail mounted methods • Gantry Method

  46. 140 T breakdown crane • Requires more block with OHE grounded, but the best option in emergency or where the site is very difficult • Work to be done after taking approvals • Mechanical department responsible

  47. 140 T breakdown crane

  48. Schematic drawing for replacing girder using 140 T crane

  49. Track mounted steam crane

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