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Feb ~8 05 09:23a Cit~ of Falcon Hei~hts 6516448675 p.3 . SUMMARY . The wheel loads of heavy trucks contribute to various fmms of pavement dis!tess. Of the various typeS. fatigue (which leads 10 cracking) and permanent deformation (rutting) are of greal importance and are the primary focus in this study. Among heavy trucks. all do not cause equal damage because of differences in wheel loads, number and location of axles, types of suspensions and tires. and other factors. Further. the damage is specific 10 the properties of the pavement, operating conditions. and environmental factors. The mechanics of truck pavement interaction were studied 10 identify relationships between truck properties and damage (fatigue and rutting). Compnter models of trucks were used to generate representative wheel load histories characteristic of the different trucks and operating conditions. Rigid and flexible pavement strUcnrral models were used to obtain pavement "influence functions" which characterize the pavement response to tire loads at any location on the roadway. The pavement responses arising from the combined loads from all wheels of a truck were then evaluated to estimate overall pavement damage caused by each truck. The study assessed the significance of truck. tire, pavement, and environmental factors as determinants of pavement damage. While most of the findings reinfoICe the existing understanding of pavement damage from heavy truck loads the treatment in this study provides a systematic overview of the interactions, as well as new insights on the mechanics involved. It is of most interest to examine the findings from the perspective of the truck characteristics that affect pavement damage. and the pavement and environmental factors that influence sensitivity to truck wheel loads. ; TRUCK CHARACTERISTICS AFFECTING PAVEMENT DAMAGE Fatigue damage to rigid and flexible pavements is most directly determined by maximum axle loads and pavement thickness. Fatigue damage varies over a range of 20: 1 with typical variations in axle loads and over the same range with typical variations in pavement thickness. Other vehicle properties have a smaller, but still significant. influence on fatigue. The relationships between damage and certllin truck properties of interest are discussed below: . Axle loads-Fatigue damage is dominated by the most heavily loaded axles because of the power-law relationship of load and fatigue. The first-order determinant of overall fatigue damage for a vehicle combination is the sum of the ESALs (Equivalent Single Axle Loads) for each axle. Typical truck axle loads vary from 10,000 to 22,000 Ib (10 10 22 kips). Assuming a 4th power damage relationship. a 22-kip axle is 23 times as damaging as a 1 Q-kip axle. Although the relative fatigue damage varies with the elCpOnenl assumed in the power law, the importance of axle load dominates for all reasonable val\les of the elCpOnent . IX