The Benkelman Beam is a pavement deflection measuring device used to check the load vs. deflection response of a pavement structure. Most often used on flexible pavement sections.
The test is done by starting with a relatively heavy load such as an 18 kip axle load. This load would be distributed on a dual wheel axle such that each tire carries 4500 lbs. You start the test by placing the beam extension between the dual wheels at their exact centerline and zero the deflection gauge. This is the maximum deflected position. You then pull the vehicle forward at a predetermined interval, usually 6 to 9 inches at a time, stopping at each interval to record the deflection change. Repeat this until there is no deflection change (usually about 4 to 5 feet out). You may then plot a deflection response curve of the pavement structure. You may then backcalculate modulus values and can determine the structural response/capacity of the pavement.
