Accurate estimation of the impact of truck loading on pavement is dependent on the magnitude and frequency of applied loads. The effect of these loads is transferred to the pavement structure through the tires. Therefore, a full understanding of the interaction between tires and pavement is necessary to analyze pavement response to truck loading.
Researchers at the Illinois Center for Transportation (ICT), led by ICT director Imad Al-Qadi, have been studying the distribution of contact stresses at the tire–pavement interface with the ultimate objective of quantifying their effect on pavement responses.
The approaches currently adopted to study the effect of traffic load on pavement damage assume that a tire load causes a uniform vertical contact stress equivalent to the tire’s inflation pressure. According to these approaches, contact stresses increase uniformly with the increase of tire load, but the contact area remains constant, or vice versa—meaning that the contact stresses remain unchanged while the contact area grows in proportion with the increased load.
The theoretical work conducted by ICT researchers and validated by experimental measurements, however, has proved these assumptions erroneous. Tire loading generates contact stresses in three directions—vertical, transverse, and longitudinal—and, on the basis of experimental measurements, the researchers have shown that the change in contact stresses resulting from the change in inflation pressure is non-uniform.
The researchers at ICT developed numerical models for commonly used truck tires with the purpose of predicting a tire’s three-dimensional, non-uniform contact stresses. The models were extended to analyze the contact that simulates tire–pavement interaction in a more realistic way. Al-Qadi, an internationally renowned expert on tire–pavement interaction modeling, explains, “ICT’s talented students and research team developed tire models, with impact on pavements in mind, to accurately predict contact stresses while avoiding the use of expensive measurements.”
“Hao Wang, a former student and currently an assistant professor at Rutgers, did a great job in this field as my first student to work on this, and Jaime Hernandez, a current Ph.D. student, has been instrumental in the recent developments, Al-Qadi adds.
The models were validated with measurements conducted in South Africa and by Michelin Tire Co. “We are very pleased with the outcome,” says Al-Qadi. “This approach will allow for a better understanding of pavement design and pavement life estimation and a more accurate prediction of when pavement damage might happen and what types to expect.”
To overcome the use of complex modeling and allow for easy implementation by engineers and practitioners, the research team also developed a database of predicted contact stresses, taking into consideration various parameters such as tire type, applied load, inflation pressure, pavement structure, temperature, and speed.
Results of this analysis emphasized the importance of considering a realistic contact stress distribution when investigating pavement responses under various loading and tire pressure conditions.
A team of talented graduate students has been working on this project: Jaime Hernandez, Angeli Gamez, Mojtaba Ziyadi, and Erman Gungor, and research associate Maryam Shakiba. The team is led by research assistant professor Hasan Ozer.
The study is conducted in cooperation with Texas A&M as part of the Asphalt Research Consortium (ARC) under a cooperative agreement with the Federal Highway Administration (FHWA). The consortium consists of several organizations striving to improve understanding of the mechanisms of asphalt pavement failure modes and to employ this in-depth understanding to devise test methods for predicting pavement performance. The project is also partially sponsored by a pooled-fund study comprising nine states, FHWA, and the tire industry.