What is the general difference between the FWD and instrumented Benkelman Beam?
The FWD applies an impulse to the road surface by a specially designed loading system which represents the dynamic short term loading of a heavy wheel load. For example, the Dynatest FWD produces an impact load of 25-30 ms duration, and a peak force of up to 120 kN (adjustable). The deflection bowl response of the pavement is measured with a set of 7-9 precision geophones at varying distances from the loading plate. The Benkelman Beam, instrumented for automatic recording of the full bowl shape, measures responses under a slower and variable loading time. As the wheel load is positioned close to the point of maximum deflection during set up, the effective load duration is longer at close offsets than at the more distant points.
