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Impact of traffic overload on road pavement performance

Publication . Pais, Jorge; Amorim, Sara I.R.; Minhoto, Manuel

Traffic on a road pavement is characterized by a large number of different vehicle types, and these can be considered in pavement design by using truck factors to transform the damage they apply to the pavement to the damage that would be applied by a standard axle. The definition of the truck factors to convert trucks into standard axles or load equivalent factors to convert axles into standard axles is carried out by considering the average loads for each axle. This process includes the vehicles that travel with axle loads above the maximum legal limit. There are also a substantial number of overloaded vehicles in terms of total vehicle weight. These axles/vehicles cause significant damage to the pavements that increases the pavement construction and rehabilitation cost. Thus, this paper investigates the impact of overloaded vehicles on road pavements by studying the truck factors for different vehicle cases applied to a set of pavements composed by 5 different asphalt layer thickness and 5 different subgrade stiffness moduli. The study revealed that the presence of overloaded vehicles can increase pavement costs by more than 100% compared to the cost of the same vehicles with legal loads.

2013Journal article

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A model for equivalent axle load factors

Publication . Amorim, Sara I.R.; Pais, Jorge; Vale, Aline C.; Minhoto, Manuel

Most design methods for road pavements require the design traffic, based on the transformation of the traffic spectrum, to be calculated into a number of equivalent passages of a standard axle using the equivalent axle load factors. Generally, these factors only consider the type of axle (single, tandem or tridem), but they do not consider the type of wheel on the axles, i.e., single or dual wheel. The type of wheel has an important influence on the calculation of the design traffic. The existing design methods assume that the equivalent axle load factors are valid for all pavement structures and do not consider the thickness and stiffness of the pavement layers. This paper presents the results of the development of a model for the calculation of the equivalent axle load factors considering the type of axle, the type of wheel and the constitution of the pavement. The model was developed based on the tensile strain at the bottom of the asphalt layer that is responsible for bottom-up cracking in asphalt pavement, which is the most widely considered distress mode for flexible road pavements. The work developed in this study also presents the influence of the type of wheel (single and dual) on pavement performance. The results of this work allowed the conclusion that the equivalent axle load factors for single wheels is approximately 10 times greater than for a dual wheel. This work also proposes average values for the equivalent axle load factors. An artificial neural network was developed to calculate the equivalent axle load factors.

2015Journal article

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