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F~b 08 05 09:23a Cit~ of Falcon Heights 6516448675 p.3 . SUMMARY . The wheel loads of heavy trucks contribute to various fol1IlS of pavement distress. Of the various types, fatigue (which leads 10 cracking) and permanent deformation (rutting) are of great 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 faclOtS. Further, the damage is specific to the properties of the pavemen~ opernting conditions, and environmental fllClors. The mechanics of truck pavement interaction were studied to identify relationships between truck properties and damage (fatigue and rutting). Computer models of trucks were used to generate representative wheel load histories characteristic of the different trucks and operating conditions. Rigid and flexible pavement structural models were used to obtain pavement "influence functions" which characterize the pavement response 10 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 reinforce 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 fmdings 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: I 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 certain 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 to 22 kips). Assuming a 4th power damage relationship, a 22.kip axle is 23 times as damaging as a 1(}.kip axle. Although the relative fatigue damage varies with the exponent assumed in the power law, the importance of axle load dominates for all reasonable vall,les of the exponent. . ix