Benkelman Beam Deflection Test, Transportation Engineering, Civil Engineering.

Benkelman Beam is a simple lever-arm device that measures the deflection of flexible pavements under the action of moving wheel loads. The probe beam, supported by a rigid reference beam, measures deflections using its 2.44m (8ft) probe end and a dial indicator at the end of the fulcrum. 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.