Falling weight deflectometers (FWDs) apply a load to the pavement surface that is generated by dropping a mass onto a hit bracket. The resulting impact generates the force that is transmitted to the pavement through a contact plate. A spring set between the falling mass and the hit bracket buffers the impact by decelerating the mass. The greater the deceleration, the greater the force generated. The amount of force generated is a function of the stiffness of the spring set, the amount of mass, and its velocity when it strikes the spring set, plus any dampening that may be part of the system. The Dynatest Model 8000E FWD is used for monitoring pavement sections in the Strategic Highway Research Program (SHRP) Long-Term Pavement Performance (LTPP) study. During the course of the study, several buffer changes were made. To evaluate the effects the buffers have on the loads and deflections, tests were conducted using each buffer set on three pavement structures near the SHRP North Central Regional Office. The results show the various buffer shapes had an effect on the test results. The differences observed are not considered significant for routine production testing but are expected to be relevant in research work involving viscoelastic materials (asphalt) and dynamic deflection analysis. (Author/publisher)
Abstract