Volume 22, Issue 5 (2022)                   MCEJ 2022, 22(5): 187-201 | Back to browse issues page

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1- Sharif University of Technology
2- Shahid Rajaee Teacher Training University , m.yekrangnia@gmail.com
Abstract:   (474 Views)
In this research, the adequacy of the method recommended by the Iran highway asphalt pavement code (Code 234) for pavement design is investigated. Pavement design in Iran highway asphalt pavement code is in accordance with the ASHTO method. Design variables in this Code are considered as Deterministic and without probability distribution; while the Average Daily Traffic (ADT), the annual growth rate (r), and the variables related to resistance such as modulus of elasticity and thickness of each layer, despite the segmentation, have many changes along a route. As a result, pavements designed on this basis may have a shorter useful life than expected and be destroyed in less traffic or age than the initial design. Iran highway asphalt pavement code uses a method similar to First Order Second Moment (FOSM) to consider the reliability in pavement design. FOSM is an old and simple method. This method has low accuracy in calculating the confidence level, especially for nonlinear functions. There are more accurate methods such as First Order Reliability Method (FORM) and Sampling for reliability analysis that eliminate the disadvantages of the FOSM method and perform reliability analysis more accurately for nonlinear functions. Therefore, it is better to consider the uncertainty of the variables and use accurate reliability methods to calculate the level of pavement reliability. A reliability-based method is proposed to improve the pavement design based on the Iran highway asphalt pavement code. To compare the two methods, traffic data and pavement condition of the Qom-Salafchegan route were collected. At first, the variables were considered Deterministic and without probability distribution, and the overlay thickness was calculated at a confidence level of 80% based on code 234. Then the most appropriate probability distribution of variables was determined by the Anderson-Darling test. According to the thickness of the overlay obtained from the Iran highway asphalt pavement code, the confidence probability of each section was determined by the FORM and Sampling methods of reliability in the Rtx software and Monte Carlo simulation in the R programming language. Based on Code 234, the pavement reliability was approximately 20% higher than that of the proposed method. Furthermore, based on this code, the required overlay thickness was about half of that determined according to the proposed method with an equal reliability level, which leads to was destroyed less traffic and lifetime than the design value and needed repair again. In the following different reliability, methods are compared with each other. According to the sampling method with a higher probability of failure than the FORM method, the required overlay thickness is determined and therefore, leads to a more conservative overlay thickness. To evaluate the accuracy of Rtx software, a Monte Carlo simulation is performed in the R programming language. It was concluded that Rtx results in the overlay design at a lower reliability level than the R programming language. In the ASHTO method, the logarithm probability distribution of wt18 and w18 variables is considered normal. This hypothesis was rejected by performing the Anderson-Darling test on the collected data and these variables do not have a normal distribution.
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Article Type: Original Research | Subject: Roads and Transportation
Received: 2022/03/18 | Accepted: 2022/06/26 | Published: 2022/07/1

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