1. PROJECT REPORT
DESIGN CONCEPTS OF BOW STRING GIRDER (40 M SPAN) OF ROAD OVERBRIDGE AND DESIGN OF SUB STRUCTURE FOR THE SAME.

2. PRESENTED BY 1. R.M.MEENA 2. SIVA KUMAR (AXEN/Designs/MTP®/MS/S.R.)
(XEN/C/JU/NWR)
2. SIVA KUMAR (AXEN/Designs/MTP®/MS/S.R.)
3. L.N.LOKHARE
(AXEN/C/KTT/WCR)
4. L.B.SINGH MAURYA
(Vice Principal/SRETC/TBM/S.R.)

3. INTEGRATED COURSE BATCH NO-514
PROJECT GUIDE
Sri.G. Bansal
COURSE DIRECTOR
Sri A.K.Rai

4. INTRODUCTION
On Indian Railway there are Nos of manned level crossings and Nos of unmanned level crossings as on date. These Level crossings are affecting the safe & effective functioning of Railways. The Level crossings are the accident prone zones and causes delay of trains due to detention by road traffic at gate.

5. INTRODUCTION- cont
There are loss of valuable human life and Railways properties due to accidents taking place on this level crossings. Keeping safety point of view it become necessary to replace these level crossings by ROB/RUB..

6. INTRODUCTION- cont
Replacing the level crossings with ROB/RUB are being done by Railways in a phased manner based upon its TVU. Where ever possible ROB is preferable over RUB due to its less maintenance, effective usefulness, even though the initial cost of ROB is more.

7. SCOPE OF THE PROJECT The ROB comprises following different structure:-
1. Main railway span (40 m)
2. Approach spans having 20 m spans
3. Abutment
4. Reinforced earth retaining wall beyond abutment on the approaches where height is less than 4.0 m

8. SCOPE OF THE PROJECT - cont
As far as super structure is concerned only design concept of Bow string girder is emphasized. However for substructure complete design is made and enclosed.

9. ELEMENTS OF BOW STRING GIRDER
MAIN I- GIRDER
Main I- girder is purely a tension member because of its geometry. This member is proposed as a prestressed member .The amount the prestressing required shall be less since the same required only nullify the tension.

10. ARCH MEMBER
SUSPENDERS
MAIN I GIRDER

11. ARCH MEMBER
Arch member is always in compression and hence RCC is sufficient to take this load. A member size of 450x900 at supports and 450x600 at crown is normally sufficient to carry the compression for this 40 meter span.

12. SUSPENDERS
Since suspenders are pure tension members and it does not requires any flexural rigidity , these members can be provided as HTS strands firmly anchored between main I beams and arch members

13. CROSS GIRDER
Cross girder can be of RCC, which spans between main I -girders. The spacing of cross girders is kept as 4.15 meter & the span is 8.0 meter. At the top of cross girder, a continuous slab of span of 4.15 meter and thickness of 230 mm is provided. Over the slab road-wearing surface as per IRC, specification is provided.

14. PLAN AT DECK LEVEL BOW STRING CROSS GIRDER 8m 41500 C LINE OF SPAN L
C LINE OF BEARING L
CROSS GIRDER 8m
4150
41500
PLAN AT DECK LEVEL

15. LOADING Live load Combinations are
Load as per IRC-6
Combinations are
1. Single lane 70R wheeled/track vehicle
2. Two lane IRC –class A, wheeled

16. ADVANTAGES OF BOW STRING OVER DECK TYPE GIRDERS
There is some considerable savings in depth of construction in case of bow string girder compared to typical deck type girder Due to reduced depth of construction, the over all length of ROB get reduced and overall economy achieved

17. 7500
ROAD SURFACE
2500
DEPTH OF CONSTRUCTION=2.50m
BOX GIRDER TYPE ROB

18. BOW STRING GIRDER TYPE ROB
7500
BOW STRING GIRDER
ROAD SURFACE
2400
1000
DEPTH OF CONSTRUCTION=1.0m
BOW STRING GIRDER TYPE ROB

19. DESIGN CONCEPT OF BOW STRING GIRDER
LIVE LOAD
Like our railway bridge rules, these IRC codes does not provide any EUDL,so for the above rolling loads maximum bending moment and shear force shall be worked out using STAAD-PRO 2003 software. However a manual calculation is also shown. Due provision for impact is also considered as per the code.

20. DEAD LOAD
This comprise of dead load of all element of bow string span ,the carriage way wearing coat, foot path and other miscellaneous load such as cables, parapets, crash barriers have been considered

21. WIND LOAD
Wind load is arrived at as per IS 875 part-III.the wind intensity multiplied by the projected area gives the wind load on the structure.

22. SUB STRUCTURE
The substructure consists of two numbers of 1.80 meter dia column spaced at 8.0 meter apart. The depth of trestle beam is fixed as 1.25 meter for stiffness and other practical consideration such as requirement during construction and replacement of bearing.

23. ELEVATION OF SUBSTRUCTURE
8.0m
1.25m
6.525m
1.80m
COLUMN 1.80m dia
Rail level
PILE CAP
PILE 1.0m dia
ELEVATION OF SUBSTRUCTURE 4

24. LOADS AND OMENTS ON COLUMN
As we know the the column is critical at the pile cap level . Maximum moments will come at this level which are all explained through the following sketches. Algebraically adding all the moments the column section is designed

25. SESMIC LOAD
Lateral Seismic Coefficient=0.04
Importance Factor =1.5 (for important bridges)
Foundation system factor =1.0 (for pile foundation)
Design for seismic force=.04x1.5x1.0=.06

26. SESMIC LOAD Code followed IRC 78
Even though the seismic load does not affect the super structure, the impact on the substructure design is considerable.
Seismic Zone III

27. Lumped mass of super structure
Adjoining span -20m
Bow string span- 40m
Lumped mass of super structure
Lever arm
Pile cap
1.DUE TO DEAD LOAD
Pile

28. 2.DUE TO DL OF SUB STRUCTURE Adjoining span -20m Bow string span- 40m
Lumped mass of trestle beam
Lever arm
Pile cap
2.DUE TO DL OF
SUB STRUCTURE
Pile

29. higher load * y-lower load *x
Adjoining span -20m
Bow string span- 40m y x
Lower load
Higher load
Un balanced moment =
higher load * y-lower load *x
Pile cap
Pile

30. 4. DUE TO LIVE LOAD Adjoining span -20m Bow string span- 40m 1.83 m
Lever arm
Pile cap
4. DUE TO LIVE LOAD
Pile

31. Foundation
The foundation system consists of four no of 1.0m dia pile spaced at 3.0m apart. The piles are proposed to be founded on hard strata, which is available at 25.0m depth. The piles are of bored cast in situ.

32. Foundation Max. vertical Load in pile workout to be :-
under seismic condition = 264 tonnes
under normal loads = 214 tonnes
lateral load per pile = 14 tonnes

33. Foundation Vertical load bearing capacity of pile = 320 t
The above capacity of piles is based on soil capacity at site. The pile derives its capacity both from friction as well as end bearing.

34. FOUNDATION Reinforcement design of pile
The length of fixity of pile below ground level “Le” is found based on lateral modulus of subgrade reaction of the pile
The moment on pile = Horizontal load x Le
Based on the moment and the vertical load on the pile,the reinceforcement of the pile is designed

35. Pile cap
L1=2.5m Le
5.318m
L=22.5m
CALCULATION OF LENGTH OF
FIXITY OF PILE