Girder launching and Re g irdering

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

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

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

40. Crawler Mounted Mechanical Crane

41. Tyre Mounted Hydraulic Crane

42. 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

43. Well designed lifting girder

44. Site Condition #2

45. 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

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

47. 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

48. 140 T breakdown crane

49. Schematic drawing for replacing girder using 140 T crane

50. Track mounted steam crane