Calibration of 4PB Tests Taking into Account Shear Forces and other Equipment Factors

ABSTRACT In pavement design the four point bending test (4PB) and other bending devices are used to determine the stiffness and fatigue characteristics of bound pavement materials. In case of the 4PB test the theory for processing and interpretation of the data is based on the bending of a slender beam in which the deflection due to shear forces is neglected. Although the error due to this neglect will be small, it is unwanted in view of calibration. Overhanging beam ends and moving masses next to the weight of the beam will also influence the measured response in dynamic 4PB tests. All these factors are discussed and solutions are presented to take these factors into account in the processing of the data. Based on preliminary finite element calculations it is found that the correction coefficient for the effect of deformation of the cross section of the beam is not equal to 2/3 but will be in the order of 0.85 for commonly used beams in asphalt research.