Evaluation of Axle Equivalency Load Factors Based on the Fatigue Criterion of Asphalt Layer Using Dissipated Energy Method and Compared with Proposed Factors in Asphalt Pavement Regulations of Iran Roads

Equivalency load factor is one of the most important factors in design of pavement، that shows the influence of traffic on pavement distress. This factor can be defined experimentally according to Asphalt Pavement Regulationd of Iran Roads (Publication 234) and the only concern in choice of the factor is the type of the axle (single، tandem and tridem) no matter whether wheels are single or dual. In this study equivalency load factor of heavy axle load mentioned in Asphalt Pavement Regulation of Iran Roads was determined based on two approaches: Strain and dissipated energy and according to the fatigue criterion and then compared to the equivalency load factors in AASHTO and Asphalt Institute regulation. 3D-Move program was used to analyze pavement sections (thin، medium، and thick) and in three vehicle speeds 10، 50 and 100 km/h at the bottom of the asphalt layer. The results showed that equivalency load factor of single axles with single wheels is independent of pavement thickness number، vehicle speed and applied method in calculation of this factor. Also، it was observed that equivalency load factor of single axle in the maximum distress method has the same quantities for both strain and dissipated energy method. In this research، equivalency load factor of single axle with dual wheels obtains less than one for single axle with single wheel with similar weight that it needs to pay attention to this matter in Asphalt Pavement Regulation of Iran Roads. Also، equivalency load factor of AASHTO and Asphalt Institute are less than the calculation values obtained in this study.