Measuring Dynamic Vehicle Loads

• The fifth objective of the AASHO Road Test was as follows: "To develop instrumentation, test procedures, data, graphs and formulas which will reflect the capabilities of the various test sections; and which will be helpful in future highway design in the evaluation of the loadcarrying capabilities of existing highways and determining the most promising areas of further highway research." It was with this objective in mind that development of equipment for measuring the dynamic load transmitted to the pavement and bridge structures through the tires of a moving vehicle was undertaken. Past research and study has shown that the load transmitted through the tires of a vehicle in motion is not constant but varies in frequency and magnitude with many factors such as the pavement profile, vehicle speed, tire pressure, tire size and the vehicle suspension system. An adequate means of making a continuous record of the frequency and magnitude of these load variations was not available when the development reported herein was undertaken. For many years studies of pavement deflections and slab strains were considered to be of value in determining the strength, design and future life of pavements; however, these measurements could only be determined under static load conditions or at best under creep speed load. It has long been observed that information on pavement behavior relating to loads applied by moving vehicles would be of value when compared to data collected under static load conditions. There are many other areas of highway and vehicle research and design where the relationship between dynamic load and other measurable characteristics would be of value, including bridge impact, loading due to pavement roughness, cracking, rutting and joints and the loads due to various vehicle suspension systems.