High-intensity load, vehicle speed, and pavement temperature are the critical factors that accelerate damage in the bituminous layers of the pavement. While the influence of speed and temperature can be quantified, the complexity in estimating damage arises in terms of understanding the load transfer at the tire-pavement interface. The load transferred to the pavement is dynamic and depends on the surface roughness, the gross vehicle weight, and vehicle manoeuvre (constant speed, acceleration, deceleration, and braking). For a realistic estimation of stresses and strains in the pavement, it is necessary to consider the dynamic load transferred from a truck to the pavement. The roughness of the pavement and driving manoeuvre influences the dynamic load transferred. This seminar talk will address two issues here. The first is related to dynamic load transfer during vehicle manoeuvre, and the second is associated with the computation of stresses and strains for such critical loads for a sample pavement cross-section.

In this seminar talk, three driving manoeuvres are considered: constant speed, acceleration, and braking. Three different road roughness profiles (Grade A, B and C as per ISO:8606) was used. A commercial vehicle dynamics software, TruckMaker, was used for computing dynamic load transferred. A two-axle truck with three types of loading (unladen, laden, and overloaded) based on the static axle load data collected from National Highway-21 in India was considered for simulation.

The ESAL value calculated using the dynamic load simulated at a constant speed of 30 km/h on a grade C profile was found to be nearly 85% higher than that calculated using the respective static load. During an acceleration manoeuvre, the variation in dynamic load was found to be 91% higher than that during a constant speed manoeuvre. Among the different vehicle manoeuvres, braking plays a critical role in the dynamic load transfer. The braking manoeuvre can be classified into three types depending on the amount of braking force applied. Dynamic loads were simulated corresponding to slow, medial, and panic braking manoeuvres for the three loading conditions of a truck on the three road profiles, A, B and C. The dynamic loads simulated for an overloaded truck was found to be nearly twice as that of static loads for the panic braking condition on grade C profile. It was also found that the wheels of unladen truck slips and locks completely during panic braking manoeuvre for all the three speeds (30, 50 and 80 km/h) and the three road profile conditions. The longitudinal force in the direction of motion between the tire and pavement during such circumstance increases drastically to 95 kN in the front axle.

The stress-strain response of pavement system for the dynamic loading during acceleration and braking are also considered in the study. A 17% increase for the horizontal tensile strains were observed for an unladen truck accelerating on grade C profile, and this is expected to cause a 46% reduction in fatigue life. While the damage equations have inherent reliability, the variability in strain values due to dynamic loads can lead to lower reliability for the pavement systems.