Benkelman beam deflection studies

it will help to study the working of benkelman beam on site.

1. Benkelman Beam Deflection Studies Transportation Engineering Section

2. Introduction

3. Benkelman Deflection Studies (IRC-81:1997) Pavement Benkelman Deflection Studies (IRC-81:1997) Static Load Test Procedure wheel

4. Benkelman Beam Evaluation Of Structural Capacity Of Existing Pavement Estimation And Design Of Over Lay For Strengthening Of Weak Pavement

5. Need of E valuation Pavement deteriorate functionally and structurally with time due to traffic loading and the different climatic condition. It is necessary to evaluate the condition of existing pavement in terms of functionally and structurally.

6. OVERLAY Pavement that do not have adequate structural strength to carry out the projected future traffic will have to be reinforced by providing additional pavement layer

7. Scope

8. Performance Of Flexible Pavement Elastic Deflection Of Pavement Under Wheel Load Sub Grade Soil Type And Its Moisture Content Compaction Thickness Quality Of Pavement Course Drainage Condition Etc.

9. This test procedure covers the determination of the rebound deflection of a pavement under a standard wheel load and tyre pressure.

10. Rebound deflection Deflected Pavement Structure Bounce Back To Original Shape Deflected Surface Original Position LOAD LOAD Load removed

11. Equipment

12. Benkelman beam – Consist of slender beam of length 3.66 m. Pivoted at 2.44 m from probe. distance from pivot to dial gauge 1.22 m. Distance from pivot to front leg 25 cm. Distance from pivot to rear leg 1.66 m.

13. 2. Loaded truck Weight of truck 12 t Rear axle load 8170 kg(dual tyre) Spacing between tyres 30-40 mm. Inflation pressure 5.6 kg/sq.cm.

14. 3. Accessories – Tyre pressure measuring gauge. Thermometer(0-100 °c) with 1 ° division. Measuring tape.etc

15. Deflection survey

16. Deflection Survey 1 . Pavement Condition Survey 2.Measurement Of Deflection Done As Per IRC-81:1997

17. Deflection Measurement – Point selection – 1 km road stretch . Minimum 10 points at 50 m interval . Location Of Point – Lane Width(m) Distance From Lane Edge(cm) Less than 3.5 60 More than 3.5 90

18. Procedure

19. A B C 2.7 m 9 m

20. Select the points and marked. The dual wheel of the truck is centered above the mark. The probe of the benkelman beam is placed between the dual tyres at the marked position.

21. Dial gauge is set at 1 cm. Initial reading (s) is recorded when rate of deformation is less than or equal to .025 mm/min.

22. Truck is slowly driven (at speed 8-10 m/s appr .) at a distance of 2.7 m. and stopped. Intermediate reading (I) is recorded. Truck is driven forward a further 9 m. Final reading (F) is recorded. Pavement temperature is recorded atleast once in each hour. Tyre pressure is checked at 2-3 hrs interval during a day.

23. Calculation

24. Find (S-I) & (S-F) If deferential Reading ≤ 0.025 mm (2.5 Divisions), then True Rebound Deflection At Temp. T Is XT = 2(S-F) If deferential reading ≥ 0.025mm, then XT = 2(S-F) + 5.82 (I-F ) The pavement rebound deflection at a standard temperature of 20°C shall be calculated

25. Effect of temperature

26. Standard temp 35 °c. Correction is applied when min thickness of the pavement is 40 mm. No correction for thin bituminous surfacing severe cracking in pavement bituminous layer is striped. Cold and high altitude regions where daily temp. < 20 ° c Correction will be positive when temp blow stand. Temperature Correction will be negative when temperature above standard temperature. Correction factor is 0.01mm/ °c variation from standard temp.

27. Analysis of data

28. Over Lay Design For A Given Section Is Based Not On Individual Deflection Value But On Statistical Analysis Of All Measurements In The Section 1.Mean Deflection 2.Standard Deviation 3.Charecteristic Deflection D C = M + 2S , For NH & SH D C = M +S, for other roads

29. Concept of Over Lay Undulated Surface Cracked Surface Surface Over Lay Surface

30. Thank you