Evaluation of Deflection Criterion as a Basis for Equivalency Factors for Flexible Pavements Using Finite Element Method

Osama A. Abaza

Abstract


The employment of computer techniques in engineering design work has become an irreversible trend, using computer as the tool for modeling, analysis, and design is now the established and preferred route. In most cases, simplifications are made to achieve ease in implementation, readily verifiable results, capabilities in self-correction of errors, and well defined scope of applications, all these are normally ranked above completeness and literal precision.

The objective of this research study is to evaluate the Equivalent Single Axle Load Factors (ESALF) for flexible pavement following developed as apart of the research based on the theoretical approach, and using ESALF utilized in the AASHTO Guide for the Design of Pavement Structures for calibration which, basically depends on empirical background. To meet the objective, a technique utilizing finite element analysis is used in order to create numerical models using shell elements with SAP2000 V10 structural engineering program.

The stresses created by these axle loads will result in a maximum deflection at the top of the subgrade layer. The recorded deflection mainly depends on the assumption of either equal contact wheel radius (equal contact area) criterion or equal contact tire pressure criterion. Each of the deflection values recorded is used to develop an ESALF through the ratio of deflection to maximum value caused by the 18-kip single axle load. In general, the results show a significant difference between AASHTO ESALF, and that of the Finite Elements Method for the two criteria considered, it is advisable to test other criteria for development of equivalency factors utilizing the theoretical approach. In addition it is advisable not to use the factors generated from the theoretical approach until further testing of other criteria like the lateral strain underneath the asphaltic surface layer.


Keywords


Finite Elements, Flexible Pavements, Equivalency Factors, Deflection Criterion

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