Elastomeric Bearing as per IRC_83-2015 (Part-II).pptx

Bearing refer to a specific type of structural component used in bridge engineering to support and accommodate movements between bridge superstructures (such as deck or girders) and substructures (such as piers or abutments).

Overall, IRC 83-2015 (Part-II) provides guidelines and specifications of elastomeric Bearing.

Elastomeric bearings are to be designed, installed, and maintained correctly to optimize their performance and longevity in bridge engineering applications.

1. TESt on Elastomeric Bearing As per IRC:83 Part-II- 2015 By: Mohammad Furqan SSE (Bridge)Mumbai

2. Function of Bridge Bearings Load Transmission from Superstructure to Substructure. Permit rotary or rocking movement caused by deflection. Allows Horizontal movement of super structure due to expansion & Contraction.

3. Manufacture Test Check of Elastomeric Pad As maintenance cost of Elastomeric Pad is very low, but the replacement of Bridge Bearing requires huge investment. If Elastomeric Pad is not as per standard Specification laid down in IRC 83 Part-II,it may result in early deterioration of Bearing Pads which may lead to replacement of Bearing.To avoid such a situation Manufacturing Test check of Elastomeric Pad is required before launching.

4. Check to be conducted on Elastomeric Bearing Pads A)On Elastomer 1. General inspection. Visual Inspection ,Dimensional Tolerance,etc. 2. Chemical Composition of Elastomer like Pyrolysis Test,%CR test. B)On Steel Laminates 1.Chemical Composition of Steel Laminated Plate. C) Test on specially moulded test piece for Elastomer. (i) Hardness (ii) Elongation at break (iii) Ultimate tensile strength (iv) Accelerated aging test (v) Compression set test (vi) Adhesion Test (vii) Ozone test D)Test on complete bearings. 1. Shear Modulus 2. Compressive Stiffness 3. Shear Bond- Destructive

5. Details of Elastomeric Bearing Size of Elastomeric Pad-300x550x74 mm. The pad consists of 5 Nos of steel laminates of size - 288x538x4 Top & bottom 3 mm thick elastomer cover. 4 layers of 12 mm thick elastomer in between steel plates.

6. Acceptance Test (As per para 7.8 of IRC:83-2015 Part-II) C lassification of Lots is as under 1. Large Lot : N umber of bearings Pads 24 or larger. 2. Small Lot: Number of bearings Pads less than 24. Acceptance Test -Large Lot - ‘ Level 1 ’ Acceptance testing. -Small Lot - ‘ Level 2 ’ Acceptance testing.

7. ‘Level 1’ Acceptance testing. This will include the following tests: A. General inspection. B. Test on specially moulded test piece of Elastomer. C. Test on complete bearings.

8. 1 . General Inspection. 1. All bearings of the lot shall be visually inspected for absence of any defects in surface finish, shape or any discernible superficial defects. 2. All bearings of the lot shall be checked for Dimensional tolerances . 3. All bearings shall be subjected to an axial load corresponding to normal pressure of 15 MPa applied in stages and held constant while visual examination is made for: a. Misalignment of reinforcing plates. b. Poor bond at interface. c. Variation in elastomer layer thickness. d. Surface defects. e. Low stif fness.

9. DIMENSIONAL TOLERANCES Sr. No I TEMS TOLERANCES Remark 1 Overall plan dimensions - 0, + 6 mm Checked during Final Inspection of Complete Bearing. 2 Total bearing thickness -0, + 5% 3 Parallelism A. Of top surface of bearing with respect to the bottom surface as datum B. Of one side surface with respect to the other as datum 1 in 200 1 in 100 4 A. Thickness of individual internal layer of elastomer B. Thickness of individual outer layer ± 10% -0, +2 mm Checked during Manufacturing Stage or after destructive Testing of Bearing in Final Inspection Stage. 5 A. Plan dimensions of laminates B. Thickness of laminate C. Parallelism of laminate with respect to bearing base as datum -3 mm, +0 ± 10% 1 in 100

10. B. Test on specially moulded Elastomer test piece. Test piece shall be moulded by the manufacturer with identical compound and under identical vulcanizing conditions as used in manufacture of the bearings. A. Test for chemical properties (i)Polymer Identification (ii)Specific gravity (iii)Ash content B.Test for physical properties of Elastomer such as (i) Hardness (ii) Elongation at break (iii) Ultimate tensile strength (iv) Accelerated aging test (v) Compression set test (vi) Ozone test

11. Pyrolysis Test: If a Red colour develops during the procedure mentioned as below then it confirms Polychloroprene rubber . 0.5 Gram of Sample of elastomer + Heat → Vapours + Solution II* → Red Colour . *Solution II : Dissolve 2.0 g of Sodium citrate crystals, 200 mg of citric acid & 30 mg each of indicators bromocresol green and metanil yellow in 500 cubic centimeter of water. → → Accepted 1.Polymer Identification (As per IS:3400 Part-22 or ASTM D297)

12. Can be calculated by given formula 2. Specific Gravity Weight of Sample in Air. Weight of Sample in Air - Wight of Sample in Water S.G =

13. 3. Ash Content (As per IS:3400 Part-XXII) 1 to 5 gram sample of elastomer from moulded test piece or bearing cut sample. Adjust temperature of Furnace at 550 ± 25 deg. After 02-03 Hrs remove the crucible and weigh. → → Sample (ii) Furnace Ash (i) % Ash Content = Weight of Ash(i) / Weight of Elastomeric sample(ii) x100 Max 5% Permissible

14. Sr.No Name of Test Permissible Limits Methodology of testing 1. Hardness 60 ± 5 IRHD IRHD stands for International Rubber Hardness Degree . The hardness scale is similar to the Shore or Durometer hardness. As per IS:3400 Part-II 2 . Elongation at break Min. 400% As per IS:3400 Part-I 3 . Ultimate tensile Strength Min. 17 MPa As per IS:3400 Part-I 4. Accelerated aging test i)Change in Hardness: +5 w.r.t value at Sr.No 1 ii) Change in UTS: -15% w.r.t value at Sr.No 3 iii) Change in Elongation at break: -30% w.r.t value at Sr.No 2 The elastomer sample of specified dimension is subjected to a temperature of 100 C for a period of 72 h and then allowed to cool to room temperature The variation in physical properties is subsequently measured. As per IS:3400 Part-IV 5. Compression set test Compression set not to exceed 35% of the Initial Strain. The elastomer sample is subjected to a compressive strain of 25% at a temperature of 100 C for 24 hours. Subsequently, the sample is cooled and the residual strain is measured. The residual strain called the ”set” should not exceed 35% of the initial strain. As per IS:3400 Part-X 6. Ozone test No cracking or disintegration of the sample The sample is subjected to a tensile strain of 20% in a chamber where the temperature is maintained at 40 C and Ozone concentration kept at 50 pphm(parts per hundred million) As per IS:3400 Part-XX PROPERTIES OF ELASTOMER

15. 1. Hardness -Cylindrical Specimen: Method N- 08mm-10mm thickness. *Minimum Edge distance from point of contact to edge of test piece = 10 mm. -Permissible Limit: 60 ± 5 IRHD

16. 2(a). Elongation at Break Permissible Limit: Min. 400% Elongation. Specimen Dimension

17. → → → 2(b) Test procedure for Elongation at Break

18. 3. Ultimate Tensile Strength Ultimate tensile strength (UTS), expressed in MPa. UTS = F m W x t - F m is the maximum force recorded, in newtons. - W is the width determined at Cross-Section A. - t is the thickness of the test piece over the test length, in millimetres. Permissible Limit: Min. 17 MPa A

19. 4. Accelerated Aging Test Accelerated ageing and heat resistance tests are designed to estimate the relative resistance of rubber to deterioration with the passage of time. The elastomer sample is subjected to a temperature of 100 C for a period of 72 h and then allowed to cool to room temperature. The variation in physical properties is subsequently measured. i) Hardness: + 5 IRHD ii) UTS : - 15% iii) Elongation at break: - 30%.

20. 5. Compression Set Test Cylindrical Disk of Dia 29.0 ± 0.5 mm & Thickness 12.5 ± 0.5 mm. Permissible Limit: Not to Exceed 35% of Initial Strain.

21. 6. Ozone test Sample Specimen is subjected to a tensile strain of 20% in a chamber where the temperature is maintained at 40 C and Ozone concentration to be kept at 50 pphm (parts per hundred million). Examine them after 72 Hrs for development of Crack. Permissible Limit- No cracking or disintegration of the sample.

22. C. Test on Complete Bearings. Two bearings should be selected at random from the ‘lot’. 1. Shear Modulus 2. Compressive Stiffness 3. Shear Bond (B earings should be excluded from the accepted lot as ‘Shear bond test’ is Destructive tests.)

23. 1. Shear Modulus δ = deformation h = thickness of elastomeric pad H = horizontal force a = length of elastomeric pad b = width of elastomeric pad Test result shall be deemed satisfactory if value of G is within 0.72-1.08 Mpa as per para 4.2.1 IRC-83 Part II 2015 *T e = Total Nominal thickness of elastomer. F Z,Test = 5 Mps shall be held constant during test.

24. Photos taken during test. Experiment Setup Bearing in shear deformation

25. 2. Compression Stiffness Test result shall be deemed satisfactory if value of compression stiffness from the deflection between 30%-100% of the test load is within ± 20% of the value specified by the Manufacturer. N to be increased to N Test = 5.G.S.A/1.5 MPa, at a rate of 5 Mpa/Min) *S= Shape Factor. G= Shear Modulus A=Overall plan area of Elastomer Bearing

26. Shape Factor (As per IRC 83-2015(Part-II) Para 5.2.3.1) The compressive stiffness of the bearing depends upon the ratio of effective plan area to its force-free surface area. For Laminated Bearing shape factor given by: S = Plan area common to Elastomer & Steel Plate Perimeter of laminated plate x T e * T e= T i if thickness of outer layer is less than 03 mm. T e= 1.4T i if thickness of outer layer is more than or equal to 03 mm. Where T e & T i are the effective layer of Elastomer & individual inner layer of elastomer.

27. 3.Shear Bond test -Maximum test loading: F z , test corresponding to σ m = 12 MPa is to be held constant during the test. -The horizontal loading 2 F x , test shall be increased gradually till horizontal deflection equals to 2 T e . *T e-Thickness of Elastomer. If neither test piece shows evidence of peeling or separation at or near the interface between rubber and reinforcement Layers/Laminates, the bearing shall be deemed to have satisfactory adhesion. It's a destructive test .

28. ‘Level 2’ Acceptance testing. This will also include the same tests as in Level 1 A. General inspection. B. Test on specially moulded test piece. C. Test on complete bearings. But here, the test ‘C’ is little different as only two test i.e. ‘Test for shear modulus’ & ‘Compression Stiffness’ are conducted. (Since these are not the destructive test, the test bearings can be used in the bridge and these shall become the part of the accepted ‘lot’.)

29. Inspection and Quality Control Certificate : A ‘lot’ under inspection should be accepted by the inspector when no defect is found in the acceptance level tests and so certified. In case of any defect in the bearing, the whole ‘lot’ shall be rejected by the inspector and certified accordingly. Acceptance: Manufacture shall furnish the following to Engineer for the acceptance judgement. i)Quality Control Certificate. ii)Inspection Certificate.

30. Certification & Marking Bearing shall be transported to site after final acceptance by Engineer. Each bearing shall be uniquely & individually numbered for identification on its external surface. A label should be provided on Top & Bottom of Bearing with detailing -Manufacturer's Name. -Unique Identification number and manufactures symbol or name on one of its Edge. -marking shall be resistant to water & Normal wear & Tear. Additional Information may be marked on bearing or supplied separately. -Date of Manufacture -Bearing Dimension -Production Batch Number -Acceptance Lot Number -Specific Bridge Location -Explanation of Marking used on Bearing.

31. What 2 Check during Inspection after installation. Shear Deformation not more than 50% of height of elastomeric pad. Rotation leading to off-loading of Edge. Compression not more than 5% of height of the Pad. Malfunctioning of Elastomeric pad would result in distress either in girder or in bed block.

32. Reference (Click to download) IRC:83-2015 (Part-II) Quality A ssurance Plan ,QAP for Elastomeric Bearing Bridge Bearings by IRICEN,Pune Relevant IS:3400 Code. IS:3400 Part-II for Hardness Test IS:3400 Part-I for Ultimate Tensile Strength & Elongation at Break Test IS:3400 Part-IV for Accelerated Aging Test IS:3400 Part-X for Compression Set Test IS:3400 Part-XX for Ozone Test