In recent years, decreased fatigue life, increased rutting, and accelerated serviceability loss in flexible pavements have been attributed to the effects of increased tire pressure. This study used the federal highway administration accelerated loading facility to measure the effects of load, tire pressure, and tire type on the response of a flexible pavement. Surface deflection, surface strain, and strain at the bottom of the asphalt layer were measured. Each of these responses was affected more by load than by tire pressure. Fatigue equivalency factors were developed using an exponential relationship between the number of cycles to failure and the magnitude of the tensile strain at the bottom of the asphalt layer. Since this strain was affected more by load than by tire pressure, the equivalency factors are influenced more by load. Doubling the wheel load (from 9,400 to 19,000 lb) increased predicted damage 1,000 percent whereas doubling the tire pressure (from 76 to 140 psi) increased predicted damage only 20 percent. On the basis of these fatigue equivalency factors, it was concluded that for the pavement section studied, the effect of increasing tire pressure from 76 to 140 psi is equivalent to an axle load increase of approximately 2,000 lb. This equivalency is valid for both radial and bias ply tires.
Abstract