An Explicit Formulation for Estimation of Structural Number (SN) of Flexible Pavements in 1993 AASHTO Design Guide using Response Surface Methodology (RSM)

Document Type : Regular Article


1 Associate Professor, Department of Civil Engineering, Sirjan University of Technology, Sirjan, Iran

2 Assistant Professor, Department of Civil Engineering, Shahid Bahnar University of Kerman, Kerman, Iran


In the 1993 AASHTO flexible pavement design equation, the structural number (SN) cannot be calculated explicitly based on other input parameters. Therefore, in order to calculate the SN, it is necessary to approximate the relationship using the iterative approach or using the design chart. The use of design chart reduces the accuracy of calculations and, on the other hand, the iterative approach is not suitable for manual calculations. In this research, an explicit equation has been developed to calculate the SN in the 1993 AASHTO flexible pavement structural design guide based on response surface methodology (RSM). RSM is a collection of statistical and mathematical methods for building empirical models. Developed equation based on RMS makes it possible to calculate the SN of different flexible pavement layers accurately. The coefficient of determination of the equation proposed in this study for training and testing sets is 0.999 and error of this method for calculating the SN in most cases is less than 5%. In this study, sensitivity analysis was performed to determine the degree of importance of each independent parameter and parametric analysis was performed to determine the effect of each independent parameter on the SN. Sensitivity analysis shows that the log(W8.2) has the highest degree of importance and the ZR parameter has the lowest one.


Main Subjects

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