Inspection of Concrete Bridges

1. Inspection of Concrete Bridges

2. Bridge Inspection Systematic observation of condition and behaviour of various components/ parts of a bridge

3. Inspection Includes • Going to the bridge • Seeing the bridge with an eye of the Doctor (Engineer) with unaided as well as an aided eye. • Systematic observation over a period of time • “Thok baja ke dekhna”

4. Objectives of Inspection • To know whether the bridge is structurally safe • Will it continue to be safe • Identify actual and potential sources of trouble at earliest possible stage • To record systematically and periodically the state of the structure • To decide about the repair measures to be taken • To provide feedback to the designer and the construction engineers on those features which give maintenance problems

5. Current Scenario on IR • Concrete bridges increasing with time • Advantage of ballasted deck • Concrete – a heterogeneous material • Durability depends on many factors • Affected by environmental factors

6. A Statement - may be controversial • Concrete structures are inherently durable as compared to steel as long as they are rationally designed and constructed • Deterioration of concrete is but a result of wrong concrete mix or poor construction work quality control.

7. But… • Possibility of mistakes to happen during construction is far greater than the steel because • Most of the material of a concrete structure are supplied and assembled on site.

8. Therefore… • the examples and anomalies and defects on concrete structure, resulting from poor quality of construction or material are numerous in number and kind. • The possibility for mistakes of the type is even higher in PSC girders, where additional processes such as pre-stressing, grouting and erection of girders are necessary.

9. and… • There are certain phenomenon in concrete that occur in the inside and some which occur on the outside and thus some can be seen and some get manifested in the form of surface defects over the years. • The behaviour of those defects is not easily predictable and analysable. • Mostly it would be in the form of cracks

10. So in concrete it becomes important to • To find for cracks, which in the initial stage • study them with a view to ascertain their cause • Track their growth and movement

11. How to inspect? • Decide number of spans to be inspected each day • Scrutinize the previous years inspection notes • Try to have plan, drawings and other details of the important bridges • Go through the drawings (important bridges to identify critical locations) • Plan any special inspection equipment, temporary staging etc. (like tunnel inspection) • Don’t rush to complete – done once a year

12. Precautions • Clothing • Glasses • Shoes • Scaffolding and ladders • No short cuts please • Watch your steps and your ego too

13. Inspections – Open Line • Para 1101 SE (Works) will inspect before monsoon every year. • Para 1103 AEN open line will inspect after monsoon every year. • Para 1104 (1)(a) Important bridges and bridges that call attention by DEN/SrDEN

14. Inspection- Bridge Organization • Para 1102 SE (Br) will inspect all RCC, PSC and Composite girders within one year of installation • Para 1102 SE (Br) will inspect all these girders once in five years on planned basis • SE (Br) will measure camber of PSC girders once a year with any reliable method • Para 1105 AEN (Br) shall test check 10% of the bridges inspected by the bridge inspector

15. Special Inspection (Need based) • When signs of weaknesses discovered during routine or detailed inspection or by any other observation. • When the bridge loading is to be increased due to revised or increased loading standard. • Distressed bridges. • Exceptional events like fire, earthquake, heavy floods etc

16. What to take along? (Anne. 11/15 of IRBM) 1. Pocket tape (3 or 5 m long) 2. Chipping hammer 3. Plumb bob 4. Straight edge (at least 2 m long) 5. 30 metre steel tape 6. A set of feeler gauges (0.1 to 5 mm) 7. Log line with 20 kg lead ball 8. Thermometer 9. Probing rod 10. Wire brush 11. Mirror ( 10x15 cm) 12. Magnifying glass (100 mm dia.) 13. Chalk/water poof pencil/pen or paint 14. Centre punch 15. Callipers (inside and outside) 16. Torch light (5 cell) 17. Paint and paint brush for repainting areas damaged during inspection 18. Gauge-cum-level 19. Piano wire 20. 15 cm steel scale 21. Inspection hammer (350-450 gm) 22. Microscope 23. Binoculars 24. Camera 25. Crack meter 27. And common sense

17. What to Inspect … but before that • Work through a checklist prepared for the particular type of structure. • Should be familiar with the details of the structure and as to how it is intended to function. • Should study previous reports before conducting inspection, so that the condition of the defects noticed earlier could be checked. • Should be aware of rectification work done earlier, the same should be inspected and its performance should be recorded.

18. …and the most important • thing is to know and realize that every deterioration has a cause and the aim of inspecting official is to determine that cause

19. Routine Inspection by AEN Purpose • Whether there is any defect in structure? • If yes, what is the degree of the defect? • Is it progressing? • Is it affecting the function of the structure? • Is there any change in the environment? • Heavy rains. • Other factors like trespassing and other usage • Is it going to affect the train operation? • Is there a necessity of doing preventive work? • Does it require detailed inspection?

20. What to see? Cracks Texture of Concrete Wear and erosion of concrete Leaching of chemicals Stains such as corrosion in steel, dampness, growth of algae, marine microbes Painting coat condition Bearings Camber Other observations

21. What to see? Cracks Texture of Concrete Wear and erosion of concrete Leaching of chemicals Stains such as corrosion in steel, dampness, growth of algae, marine microbes Painting coat condition Bearings Camber Other observations

22. Cracks? Cracks identification Length Size Orientation Location Breathing of not Accompanying stains

23. Crack meter Least count 0.02 mm Measuring Magnifier - Proceq

24. Cracks? Cracks need to be analysed and then only conclusions may be drawn All cracks lead to durability problems Some cracks are not serious Require only covering Other cracks are serious Affect load carrying capacity Require retro-fitment as well as covering to prevent corrosion Tell tales help in decision making

25. Tell tales

26. Types of Cracks and spalling • Fresh concrete • Hardened Concrete • Structural Cracks • Due to loads • Compatibility cracks • Due to Detailing • Corrosion • Steel • Concrete • Others • Alkali-aggregate reaction • Sulphate attack

27. Cracks in fresh Concrete • Crazing • Plastic Shrinkage • Drying Shrinkage • Plastic settlement • Long term Drying Shrinkage • Thermal expansion/contraction • Settlement of formwork

28. Crazing • Probable Area • Against formwork or surface • Probable Locations • Fair faced slabs • Cause • Impermeable formwork, over trawling • Rich mixes, poor curing • Remedy • Improve curing and finishing • Time of Appearance • 1-7 days, sometimes later

29. Plastic Shrinkage

30. Plastic Shrinkage • Probable Area • Random over reinforcement mesh, Diagonal, Normal to wind direction • Probable Locations • RCC slabs • Cause • Rapid early drying • Low bleeding and fast surface evaporation • Remedy • Improve early curing and trowel • Time of Appearance • Thirty min. to six hours

31. Plastic Settlement

32. Plastic Settlement • Probable Area • Over reinforcement, Arching, Change of depth • Probable Locations • Deep sections, Top of Columns/ troughs • Cause • Excess Bleeding • Rapid early drying • Remedy • Reduce Bleeding • Reverberate mildly • Time of Appearance • Ten min. to three hours

33. Early Thermal Expansion and Contraction • Probable Area • External/ Internal restraint • Probable Locations • Thick walls, Thick slabs • Cause • Excess heat generation, Excess temp. gradient • Rapid cooling, Curing by cold water • Remedy • Reduce heat and/or insulate, cool concrete, reduce spacing of steel • Time of Appearance • One day to 2-3 weeks

34. Long term drying shrinkage • Probable Area • - • Probable Locations • Thin walls, Thin slabs • Cause • Absence of movement, inefficient joints • Excess shrinkage, Inefficient curing • Remedy • Reduce w/c ratio, Improve curing • Time of Appearance • Several weeks or months

35. Action in case of cracks in Fresh Concrete • For purely surface cracks, normally no action taken if appearance is not an issue • In case cracks are wider and deeper, the repair method as suitable may be decided based on the crack size. • In case of time dependent crack like shrinkage and settlement – the action should be delayed if not affecting the structure.

36. Cracks in Hardened Concrete during service

37. Compatibility cracks REINFORCED CONCRETE BEAM UNDER LOAD

38. Crack in the deck slab

39. Compatible Cracks • Cracks which occur in course of normal loading in RCC components for reinforcement to take the tensile stresses. Specified in Para10.2.1 (a) of CBC.

40. STRUCTURAL CRACKS Slabs

41. RCC Slab

42. Cross cracks in center

43. Longitudinal cracks at bottom

44. Cross cracks at ends

45. Crack near the support of cantilever

46. STRUCTURAL CRACKS Girders

47. What to inspect in concrete bridges – Major Bridges – PSC girders • All the items what are there in the small spans • In addition • Items related to pre-stressing (post tensioning) and Anchorage Zone • Slab, diaphragms, Junctions of cast in situ and precast units or RCC/PSC • Inside of the Box girder • Bearings and Expansion arrangements

48. PSC Box

49. PSC Box

50. PSC Box