Benkelman Beam Test
OBJECTIVE:
To determine the rebound deflection of a pavement under a standard wheel load and tyre pressure with or without temperature measurement by Benkelman Beam test.
INTRODUCTION
A.C. Benkelman devised the simple deflection beam in 1953 for measurement of pavement surface deflection on the WASHTO Test Road. It is widely used all over the world for evaluation of the requirements of strengthening of flexible pavements.
CONCEPT & SIGNIFICANCE:
Performance of flexible pavements is closely related to the elastic deflection of pavement under the wheel loads. The deformation or elastic deflection under a given load depends upon sub grade soil type, its moisture content and compaction, the thickness and quality of the pavement courses, drainage conditions, pavement surface temperature etc.
The Benkelman Beam Deflection Method is thus widely used for Evaluation of Structural Capacity of Existing Flexible Pavements and also for Estimation and Design of Overlays for Strengthening of any weak pavement for Highways.
DEFLECTION:
Pavement surface deflection measurements are the primary means of evaluating a flexible pavement structure and rigid pavement load transfer. Although other measurements can be made that reflect (to some degree) a pavement's structural condition, surface deflection is an important pavement evaluation method because the magnitude and shape of pavement deflection is a function of traffic (type and volume), pavement structural section, temperature affecting the pavement structure and moisture affecting the pavement structure.
Deflection measurements can be used in back calculation methods to determine pavement structural layer stiffness and the sub grade resilient modulus. Thus, many characteristics of a flexible pavement can be determined by measuring its deflection in response to load. Furthermore, pavement deflection measurements are non-destructive.
EQUIPMENT/AAPARATUS:
Benkelman Beam consists of a slender beam 3.66 mtr long pivoted at a distance of 2.440 mtr from the tip as shown in fig below and a loaded truck (8 to 10 tons).
SALIENT FEATURES OF BENKELMAN BEAM:
The equipment is light weight and made of aluminium for easy portability and use at any test location.
Length of the Benkelman beam is 250 cm and net weight is 15kg.
The apparatus is compact, unique and possess a telescopic design for quick set up and storage during transport to the test location.
The equipment is supplied in two parts for assembling on site with easy hand tools.
One end of the beam rests at a point under investigation while the beam is pivoted in the centre.
The free end carries a dial gauge to record the deflections. The other end is kept on a stable platform.
Provided with anti-vibration system for accurate measurement of pavements. Provided with dial indicator and accessories.
The beam is put in contact with the pavement under test between the tires of the vehicles.
The measurement of the deflection is carried out when the vehicle passes over the test area.
UTILITY
Direct reading of deflection dial indicators eliminates the need for conversions or calculations during measurement.
It is used to measure the deflection of the road surface when loaded by the wheels of vehicles.
ACCESSORIES
Wooden carrying case for the Benkelman Beam Benkelman indicator gauge, calibration unit, etc.
APPLICATIONS
Pavement structure analysis
Roadways construction
Road surface deflection
measurement Plate test
PROCEDURE
Deflections shall be measured as follows:
The test point shall be pre-selected and marked. For highway pavements, test point shall be located at the distances from the edge of the lane given in table below;
The tyre pressure should be checked before the first test and then at intervals not exceeding three hours.
The truck shall initially be positioned with the test wheel between 100 and 150 mm to the rear of the test spot, i.e. Position A.
The probe of the beam shall be inserted between the dual tyres of the test wheel with the toe located on the test spot.
The locking device shall be released and the rear of the beam adjusted so that the plunger is in contact with the dial gauge.
The dial gauge shall be set to road between 9 and 11 mm (the actual reading need not be recorded) and the vibrator set in operation.
The truck shall be moved forward at creep speed so that the test wheel passes over the test spot and continues advancing to position B which is 2.7+0.1 meters beyond the test spot.
The START READING, ‘S’ is the maximum dial gauge reading occurring during this movement of the truck from position A to position B, and will normally occur as the wheel passes over the test spot. This reading shall be recorded.
The INTERMIDIATE READING, ‘I’ is that figure indicated by the dial gauge at the movement the truck stops with the test wheel in the position B. This reading shall be recorded.
The truck shall be moved forward until the test wheel is in position C which is not less than 10 meters from position B.
The FINAL READING, ‘F’ is that figure indicated by the dial gauge when the truck has stopped in position C. this figure shall be recorded.
Temperature measurements must be made when the top layer of the pavement consists of 40 or more of bitumen bound material .The following procedure should be followed:
A hole should be made with the mandrel to a depth of 40mm or to such a depth that it does not break through the bitumen bound material.
The hole should be filled with glycerol or oil and the thermometer inserted.
The temperature should be recorded at least hourly, or at decreasing time intervals down to 15 minutes when successive temperatures differ by more than 3°C.
No beam readings should be made outside the pavement temperature range of 5°C to 30°C when the top layer of the pavement consists of 40 mm or more of bitumen bound material.
OBSERVATIONS
All reports shall include the following;
Name of Road
Section/Location
Lanes
Distance from lane edge.
The actual axle load used.
The rebound deflection of the pavement (to 0.01mm).
The date and time of readings.
Where temperature readings are required:
The pavement temperature.
The depth at which the temperature is recorded.
The time when temperature is taken.
Note:
If the dial gauge has been modified to road pavement deflection directly, the questions in 4.1 (b) and
(c) must be divided by 2.If the dial gauge is graduated in an anti—clockwise direction the terms within which the brackets will have to be reversed to give a positive value.
***A larger difference can be tolerated if it is confirmed while testing that the legs of the beam are not sitting in the bowl.
You can download complete procedure from below attachment.
OBJECTIVE:
To determine the rebound deflection of a pavement under a standard wheel load and tyre pressure with or without temperature measurement by Benkelman Beam test.
INTRODUCTION
A.C. Benkelman devised the simple deflection beam in 1953 for measurement of pavement surface deflection on the WASHTO Test Road. It is widely used all over the world for evaluation of the requirements of strengthening of flexible pavements.
CONCEPT & SIGNIFICANCE:
Performance of flexible pavements is closely related to the elastic deflection of pavement under the wheel loads. The deformation or elastic deflection under a given load depends upon sub grade soil type, its moisture content and compaction, the thickness and quality of the pavement courses, drainage conditions, pavement surface temperature etc.
The Benkelman Beam Deflection Method is thus widely used for Evaluation of Structural Capacity of Existing Flexible Pavements and also for Estimation and Design of Overlays for Strengthening of any weak pavement for Highways.
DEFLECTION:
Pavement surface deflection measurements are the primary means of evaluating a flexible pavement structure and rigid pavement load transfer. Although other measurements can be made that reflect (to some degree) a pavement's structural condition, surface deflection is an important pavement evaluation method because the magnitude and shape of pavement deflection is a function of traffic (type and volume), pavement structural section, temperature affecting the pavement structure and moisture affecting the pavement structure.
Deflection measurements can be used in back calculation methods to determine pavement structural layer stiffness and the sub grade resilient modulus. Thus, many characteristics of a flexible pavement can be determined by measuring its deflection in response to load. Furthermore, pavement deflection measurements are non-destructive.
EQUIPMENT/AAPARATUS:
Benkelman Beam consists of a slender beam 3.66 mtr long pivoted at a distance of 2.440 mtr from the tip as shown in fig below and a loaded truck (8 to 10 tons).
SALIENT FEATURES OF BENKELMAN BEAM:
The equipment is light weight and made of aluminium for easy portability and use at any test location.
Length of the Benkelman beam is 250 cm and net weight is 15kg.
The apparatus is compact, unique and possess a telescopic design for quick set up and storage during transport to the test location.
The equipment is supplied in two parts for assembling on site with easy hand tools.
One end of the beam rests at a point under investigation while the beam is pivoted in the centre.
The free end carries a dial gauge to record the deflections. The other end is kept on a stable platform.
Provided with anti-vibration system for accurate measurement of pavements. Provided with dial indicator and accessories.
The beam is put in contact with the pavement under test between the tires of the vehicles.
The measurement of the deflection is carried out when the vehicle passes over the test area.
UTILITY
Direct reading of deflection dial indicators eliminates the need for conversions or calculations during measurement.
It is used to measure the deflection of the road surface when loaded by the wheels of vehicles.
ACCESSORIES
Wooden carrying case for the Benkelman Beam Benkelman indicator gauge, calibration unit, etc.
APPLICATIONS
Pavement structure analysis
Roadways construction
Road surface deflection
measurement Plate test
PROCEDURE
Deflections shall be measured as follows:
The test point shall be pre-selected and marked. For highway pavements, test point shall be located at the distances from the edge of the lane given in table below;
The tyre pressure should be checked before the first test and then at intervals not exceeding three hours.
The truck shall initially be positioned with the test wheel between 100 and 150 mm to the rear of the test spot, i.e. Position A.
The probe of the beam shall be inserted between the dual tyres of the test wheel with the toe located on the test spot.
The locking device shall be released and the rear of the beam adjusted so that the plunger is in contact with the dial gauge.
The dial gauge shall be set to road between 9 and 11 mm (the actual reading need not be recorded) and the vibrator set in operation.
The truck shall be moved forward at creep speed so that the test wheel passes over the test spot and continues advancing to position B which is 2.7+0.1 meters beyond the test spot.
The START READING, ‘S’ is the maximum dial gauge reading occurring during this movement of the truck from position A to position B, and will normally occur as the wheel passes over the test spot. This reading shall be recorded.
The INTERMIDIATE READING, ‘I’ is that figure indicated by the dial gauge at the movement the truck stops with the test wheel in the position B. This reading shall be recorded.
The truck shall be moved forward until the test wheel is in position C which is not less than 10 meters from position B.
The FINAL READING, ‘F’ is that figure indicated by the dial gauge when the truck has stopped in position C. this figure shall be recorded.
Temperature measurements must be made when the top layer of the pavement consists of 40 or more of bitumen bound material .The following procedure should be followed:
A hole should be made with the mandrel to a depth of 40mm or to such a depth that it does not break through the bitumen bound material.
The hole should be filled with glycerol or oil and the thermometer inserted.
The temperature should be recorded at least hourly, or at decreasing time intervals down to 15 minutes when successive temperatures differ by more than 3°C.
No beam readings should be made outside the pavement temperature range of 5°C to 30°C when the top layer of the pavement consists of 40 mm or more of bitumen bound material.
OBSERVATIONS
All reports shall include the following;
Name of Road
Section/Location
Lanes
Distance from lane edge.
The actual axle load used.
The rebound deflection of the pavement (to 0.01mm).
The date and time of readings.
Where temperature readings are required:
The pavement temperature.
The depth at which the temperature is recorded.
The time when temperature is taken.
Note:
If the dial gauge has been modified to road pavement deflection directly, the questions in 4.1 (b) and
(c) must be divided by 2.If the dial gauge is graduated in an anti—clockwise direction the terms within which the brackets will have to be reversed to give a positive value.
***A larger difference can be tolerated if it is confirmed while testing that the legs of the beam are not sitting in the bowl.
You can download complete procedure from below attachment.
