This study aims at evaluating the effect of overlapping flexible pavement strain responses from truck axles that are not part of multiple axle configurations (i.e., tandem, triple and quad). For this purpose, a newly constructed pavement was instrumented with strain gauges installed at the bottom of the asphalt concrete base layer on US-287 south of Mansfield, TX. This pavement structure is typically used for medium- to high-volume roads in the South-Central region of the United States. The strain gauges were used to measure longitudinal and transverse strains under several passes of a test vehicle. This was a class 6 truck with a steering axle load of 56.9 kN (12.8 kips) and a tandem drive axle load of 161.9 kN (36.4 kips). The speed and the lateral position of the vehicle were recorded for each test vehicle pass. Sufficient quantities of the top two layers of asphalt concrete were obtained during construction to allow dynamic modulus testing in the laboratory. The general-purpose finite element program Abaqus was used to model the instrumented pavement section and compute the longitudinal and transverse strains at the location of the strain gauges. In the analysis, the asphalt concrete layers were modeled as visco-elastic materials. The Abaqus estimated strains were found in good agreement with the measured strains. Both the field measurements and the finite element analysis showed that the strains under the passing of the steering axle were of similar magnitude as the strains under the passing of the rear tandem axle. The measured transverse strains were in general slightly larger than the corresponding longitudinal strains. This can be attributed to the accumulation of strain from the front axle and the rear axle that takes place only in the transverse direction. However, the finite element model computed higher strains in the longitudinal direction than in the transverse direction. These findings suggest the need to account for the overlap in strain responses from the steering and the following axles of trucks. Furthermore, findings suggest that both the longitudinal and the transverse strain responses need to be considered in evaluating the fatigue damage impacted from trucks
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