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Title:Influence of tandem axle on pavement responses and weight limit equivalency
Author(s):Ramakrishnan, Aravind
Advisor(s):Al-Qadi, Imad L.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Load equivalency
Tandem axle
Strain Recovery
Abstract:Currently, pavements are designed using layered elastic theory (LET), which makes it easy to obtain the responses for a given loading configuration. However, LET minimizes the influence of axle loading configurations on pavements. Axle load limits for single (20 kips) and tandem axle (34 kips) are intended to be set so that the damage they produce is the same. In other words, axles at their corresponding weight limits are considered equivalent. Because pavement layers are more complicated than a linear elastic material, LET tends to underpredict loading responses and, hence, the damage. Therefore, to understand the effect of loading configuration on asphalt concrete (AC) behavior, Actual tandem loading and flexible pavement structure were modeled using finite element. The influence a 4.5-ft spaced tandem axle on flexible pavement responses and strain recovery were qualitatively assessed. The results showed that the effect of a tandem axle was highly pronounced for vertical strain on the subgrade, followed by that on the granular base, and then finally the transverse strain at bottom of the AC. Such responses could be approximately 1.5 to 1.75 times that of the single axle model. Stress-pulse analysis suggested that a tandem axle could be simulated accurately in laboratory tests. Although stress-pulse magnitude and shape (when no overlap is observed) are known to be independent of speed, loading-pulse duration can be calculated to identify the rest period. Similarly, domain analysis suggested that damage potential was affected by temperature and speed, which should be considered in platoon designs. Transfer functions from Mechanistic Empirical Pavement Design Guide (MEPDG) were used to compute pavement damage. Tandem axle (34 kips) and single axle (20 kips) were found to be inequivalent, confirming that the damage of the tandem axle was higher than single axle. For the given specific case, tandem axle weight of 30 kips was found to be equivalent to single axle (20 kips). This equivalency might be material, speed, tandem spacing, and structure dependent. Given the national goods movement, national weight limits should be applied after establishing an equivalency factor that consider pavement damage mechanistically.
Issue Date:2020-12-08
Rights Information:Copyright 2020 Aravind Ramakrishnan
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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