Padma Multipurpose Bridge Project, Janjira Approach Road and Selected Bridge End Facilities, Contract No. PMB/AR/01

1. WELCOME
CONSTRUCTION SUPERVISION CONSULTANT, PMBP
BANGLADESH ARMY

2. PRESTRESSING OF
BRIDGE GIRDER

3. INTRODUCTION

4. ADVANTAGE OF PRESTRESSING
The prestressing of concrete has several advantages as compared to traditional
reinforced concrete (RC) without prestressing. A fully prestressed concrete member is
usually subjected to compression during service life. The advantages of prestress
concrete are as follows:
 Section remains uncracked under service loads.
 Reduction of steel corrosion and thereby increase in durability.
 Full section is utilised.
● Higher moment of inertia.
● Less deformations (improved serviceability).
 Increase in shear, bending and torsional capacities.

5. ADVANTAGE OF PRESTRESSING
 Improved performance (resilience) under dynamic and fatigue loading.
 Sections can behave elastically.
 Larger spans possible with prestressing (bridges, buildings).
 For the same span, less depth compared to RC member.
● Reduction in self weight.
● More aesthetic appeal due to slender sections.
● More economical sections.

6. ADVANTAGE OF PRESTRESSING
 Suitabality for precast construction
● Rapid construction
● Better quality control
● Reduced maintenance
● Suitable for repetitive construction
● Multiple use of formwork
● Availability of standard shapes

7. LIMITATIONS OF PRESTRESSING
● Prestressing needs skilled manpower
● The use of high strength materials is costly
● There is additional cost in auxiliary equipments
● There is need for quality control and inspection

8. TERMINOLOGY
Post-Tensioning
The application of a compressive force to the concrete by stressing tendons or bars
after the concrete has been cast and cured. The force in the stressed tendons or
bars in transferred to the concrete by means of anchorages.
Wires
Prestressing wire is a single unit made of steel.
Strands
An assembly of several high strength steel wires wound together. Stands usually
have six outer wires helically wound around a single straight wire of a similar
diameter.
Tendon
A group of strands or wires are wound to form a prestressing tendon.

9. TERMINOLOGY
Anchorage
An assembly of various hardware components which secure a tendon at its ends
after it has been stressed and imparts the tendon force into the concrete.
Anchor Plate (Tube Unit)
The part of the anchorage which bears directly on the concrete and through which
the tendon force is transmitted.
Wedges
A small conically shaped steel component placed around a strand to grip and
secure it by wedge action in a tapered hole through a wedge plate.
Wedge Plate
A circular steel component of the anchorage containing a number of tapered holes
through which the strands pass and are secured by conical wedges.

10. GIRDER SECTION INCLUDING
REBAR PLACEMENT
Reinforcement placing (Side view) Reinforcement placing (Top view)

11. GIRDER SECTION INCLUDING
REBAR PLACEMENT
End Section Mid Section

12. SHEATHING DUCT
Raw Material for Sheathing Duct

13. SHEATHING DUCT
Preparation of Sheathing Duct

14. SHEATHING DUCT
Prepared Sheathing Duct

15. PRESTRESSING STRAND
Coil Strand (7 wire)Wire

16. STRESSING CABLE & THEIR PLACEMENT
WITHIN RABAR
Cable Profile checking of cable ductCable within the rebar inside
sheating duct

17. ANCHORAGE MATERIALS
Tube Unit (Anchor Plate) Wedge Plate Wedges

18. CONCRETE MIX DESIGN
Concrete class : C50
28 days cube strength : 50 mpa
Materials
Cement : Bashundhara (Ordinary Portland Cement) OPC
Fine Aggregate : Sylhet Sand, Bangladesh
Coarse Aggregate : Meghaloy, India
Admixture : Master Polyheed 8632
Water Cement Ratio : 0.3
Slump : 150mm ~ 200mm

19. CONCRETE MIX DESIGN
Batch Weight per cum of Concrete on SSD Condition
Cement : 470 kg
Water : 141 kg
Fine Aggregate : 658.6 kg
Coarse Aggregate : 1152 kg
Admixture : 5.9 kg
Mix Proportion : Cement : Sand : Stone
1 : 1.40 : 2.45

20. CONCRETING WORK OF PC GIRDER
Girder ready for concreting Concrete Transit Mixer Car Slump Test

21. CONCRETING WORK OF PC GIRDER
Concreting is going on Form Vibrator

22. CURING

23. PRESTRESSING JACK & ITS FUNCTION
Jack (Front Side) Jack (Back Side)

24. PRESTRESSING JACK & ITS FUNCTION
Jack Setting Prestressing Pump Machine

25. GIRDER END ARRANGEMENT
FOR PRESTRESSING
Tube Unit Wedge Plate

26. GIRDER END ARRANGEMENT
FOR PRESTRESSING
Collar Setting Safety Protection

27. GIRDER END ARRANGEMENT
FOR PRESTRESSING
Master Grip
Inserting
Master Grip
Inserting
Master Grip
Jack
Setting

28. PRESTRESSING PULL (ELONGATION)
FROM BOTH END
1st Reading : 62 mm Final Reading : 163 mm Reading after lock off : 153 mm
Slip : 163-153= 10 mm

29. PRESTRESSING PULL (ELONGATION)
FROM BOTH END
Work supervised by CSC Engr. Reading just after stressing : 200 mm Reading after 24 hours : 200 mm
After 24 hours slip: 200-200=0

30. STRUCTURE LOAD ON EACH GIRDER AND HOW IT IS
MAINTAINED BY PRESTRESSING
Total load (LL+DL) on each 30m girder = 1643.19 kN
Jacking force on each cable = 2475 kN (As per Contract Drawings)
Jacking force on each girder (3 no cable) = 2475 x 3 = 7425 kN
Hence 7425 kN>1643 kN
Factor of Safety, FS = 7425÷1643 = 4.5 [Minimum FS is required 1.5]
So Girder is safe.

31. PRESTRESSING PULL IS CONVERTED INTO STRESS
Jacking force, F = 2475 kN [As per Contract Drawings]
= 2475÷0.96 [Jack efficiency 96%]
= 2578.125 kN
= 2578.125 x 1000 N [1 kN = 1000 N]
= 2578.125 x 1000÷9.81 kg [1 Kg = 9.81 N]
= 262805.81 kg
Jacking Ram Area, A = 563.72 cm2
Stress = Force/Area = F/A = 262805.81/563.72 kg/cm2
= 466.19 kg/cm2

32. HOGGING & IT’S MEASUREMENT
After Stressing Hogging at centre : 33 mm Measurement taking by level machine

33. BUCKLING & IT’S MEASUREMENT
After Stressing Reading at end section : 100 mm Reading at max buckling point
90 mm

34. GROUT MIX DESIGN
Water cement ratio : 0.45
Mix proportion : Water : Cement : Admixture (Cebex-100)
22.5 Kg : 50 Kg : 1 Pkt

35. GROUTING PROCESS
Setting Grout Inlet Pipe Washing Duct Pipe by Air
Compressor
Washing Duct Pipe by Air
Compressor

36. GROUTING PROCESS
Pouring Water in Agitator Pouring Cement in Agitator Mixing Grout Materials in Agitator

37. GROUTING PROCESS
Grouting Pump Machine Grout Come out from Agitator Grouting in Progress

38. GROUTING PROCESS
Grout Come out from Outlet Pipe Lock off Outlet Pipe Provide Pressure 5.25 Kg/cm2

39. WEIGHT OF 30M GIRDER

40. CRANE CAPACITY

41. PIER CAP SEAT ARRANGEMENT

42. BEARING PAD (ELASTOMERIC PAD)
Size of Bearing Pad : 500 x 250 x 60mmPlan of Bearing and Pedestal

43. BEARING PAD (ELASTOMERIC PAD)

44. BEARING PAD (ELASTOMERIC PAD)

45. PLACING OF RUBBER BEARING PAD
(ELASTOMERIC PAD)
Bearing Pedestal Placing Bearing Pad on Pedestal

46. PLACING OF GIRDER ON BEARING PAD

47. TIEING WITH CRANE AT GIRDER END

48. GIRDER LIFTING AND PLACING

49. GIRDER LIFTING AND PLACING

50. LEAVE THE GIRDER AFTER PLACING
ON PIER CAP
Cross Girder Rebar is
welded for Tieing Girders

51. GAP BETWEEN FLANGE TO
FLANGE OF GIRDER
Design Gap : 40mm Maximum Gap (Actual) : 85mm

52. GAP BETWEEN FLANGE TO
FLANGE OF GIRDER
Design Gap : 40mm Minimum Gap (Actual) : 12mm

53. GAP BETWEEN TWO GIRDER
Design Gap : 100mm Gap (Actual) : 115mm

54. CONCLUSION