Reliability-Based Design Procedure for Fatigue Cracking in Asphalt Pavements

Abstract

The need to account for design inputs variabilities effect on predicted performance has led many design procedures to address the issue of reliability for pavement applications. The Florida cracking model utilizes an empirically derived reliability for fatigue cracking design of asphalt pavements. A reliability approach, which is based on probabilistic uncertainty quantification, is necessary in order to account properly and effectively for the contribution of the variability in each parameter to the overall variance. This paper presents a load and resistance factor design (LRFD) procedure for the Florida cracking model. By delivering designs of uniform reliability, LRFD provides the basis for developing quality control and quality assurance standards. A first order reliability method (FORM) which incorporates central composite design (CCD) based surrogate model is employed to compute the reliability and formulate the partial safety factors. The reliability calibration was achieved based on field pavement sections that have a wide range in design inputs and target reliability. Illustrative designs based on the developed LRFD procedure has shown the effectiveness of the partial safety factors, and thus giving further confirmation to the credibility of the employed reliability analysis methodology. INTRODUCTIONLoad induced top-down fatigue cracking (i.e., cracking that initiates at the surface of asphalt concrete (AC) layer and propagates downward) has been observed in many parts of the world (e.g., 1-4). It is widely accepted that top-down cracking results from a critical combination of load, thermal and aging effects. A multi-year research at the University of Florida has led to the development of a new hot mix asphalt fracture mechanics (HMA-FM) framework. HMA-FM is based on visco-elastic principle and predicts the initiation and propagation of top-down cracking (e.g., 5, 6). Based on the performance evaluation of field pavement sections, a parameter termed energy ratio (ER) which relates well with the observed performance in the field was identified and introduced into HMA-FM (7). Utilizing ER as a design criterion, a mechanistic empirical (M-E) pavement design model for top-down fatigue cracking was developed. The model was calibrated and validated on a number of field pavement sections from the State of Florida and has been found to be successful in distinguishing pavement sections which exhibited cracking from those that did not. The energy ratio method has recognized the importance of accounting for the effects of uncertainty in design inputs on predicted performance, and has therefore incorporated an empirically derived reliability concept. These reliability factors were developed by fitting computed ER values of a single section with respective target reliabilities without accounting directly for the effects of design inputs variabilities on performance (8). A reliability which is not based on probabilistic method of uncertainty propagation might not give designs of uniform target reliability th...

Towards a Reliability-Based Pavement Design using Response Surface Methods

“…A two-component analytical reliability analysis methodology has been suggested by Dinegdae and Birgisson ( 12 , 20 ) for pavement reliability computation. The first component uses a RSM for generating a surrogate model for the performance function, whereas the second component computes the reliability using the Rackwitz–Fiessler (R–F) algorithm, which is one variety of the FORM.…”

“…For the evaluation of the reliability analysis methodology, pavement sections with high quality field and laboratory data in addition to well documented field performance histories are required. For this purpose, 15 pavement sections from the state of Florida with a wide range in target reliabilities and design inputs were identified and used in this study ( 14 , 25 , 30 ). The target reliabilities of these pavement sections were established by following the recommendations specified in the Florida Department of Transportation pavement design guide ( 31 ).…”

“…The first order reliability method (FORM), which is a typical example of an analytical reliability method, allows the propagation of variabilities in the design process and has been implemented for pavement reliability applications ( 10 – 12 ). Furthermore, FORM can be used to develop a reliability-based codified design procedure in the format of the load and resistance factor design (LRFD) method, which delivers pavement sections of uniform reliability level, thus providing the proper platform for life cycle cost analysis (LCCA) ( 12 – 14 ). The implementation of analytical based reliability analysis techniques for pavement application is complicated by these techniques requiring the performance function to be an explicit function of the random variables, which is unavailable in most M-E design procedures.…”

Evaluation of reliability index and probability of failure for the improvement of the Nigerian empirical mechanistic flexible pavement analysis and design system (Nempads)

“…Reliability in pavement design is introduced to consider these uncertainties. Advantages of using reliability includes the calibration of new design methods, developing rational design specifications, optimizing resources, and assessing the damage and remaining life of the pavement [7]. For example, M-E methods can adapt to new design conditions (e.g., heavier loads, new pavement materials) by relying primarily upon mechanistic pavement modelling.…”

“…In this paper, the aim is to evaluate the reliability index (RI) with respect to fatigue and rutting within the different seasons peculiar to Nigeria, in order to Improve Empirical-Mechanistic Flexible pavement roads design approach. Previous researchers like, [9], [7] and [3], all worked on similar area where they evaluated the variabilities with respect to pavement materials, environmental factors, traffic loading and finally computed component reliability index, system reliability index and probability of failure .The difference of this research with their own, is computing the reliability index with respect to the seasons peculiar to Nigeria to see the effect of environmental condition in each season.…”