| The Load Equivalency Factor (LEF) and the Truck Factor (TF) are defined as the relative damage of an axle group or a truck to that of a standard axle. The AASHTO procedure of pavement design only accounts for single and tandem axles based on AASHO road test results and does not account for damage due to axle groups with more than three axles. In the mechanistic-empirical pavement design approach, the procedures used to determine these values consists of building up the truck or axle group from its axle components and computing the damage based on Miner's hypothesis using fatigue curves obtained from single haversine or continuous sinusoidal load pulses. In this thesis, the fatigue life of an asphalt mixture under different trucks and axle groups was determined directly from the indirect tensile cyclic load test by using load pulses that are equivalent to the passage of an entire axle group or truck. The dissipated energy approach was adopted in analyzing the results and determining the number of repetitions to failure for each case, and a unique fatigue curve that can be used for multi-axle configurations was developed. Trucks consisting of up to eleven axles and axle groups of up to eight axles were studied. The results showed that the normalized damage per load carried decreases with increasing the number of axles within an axle group. Additionally, the fatigue lives predicted using single load pulses were compared to the measured ones from the different axle groups and trucks, and correction factors were developed. |
