DEVELOPMENT AND CALIBRATION OF A MECHANISTIC DESIGN PROCEDURE FOR JOINTED PLAIN CONCRETE PAVEMENTS

Abstract

The development of a mechanistic-based design procedure is currently underway in the United States. This development is being conducted under the National Cooperative Highway Research Program (NCHRP) under sponsorship by the AASHTO. This paper addresses the key aspects of the design procedure for jointed plain concrete pavements (JPCP). Design inputs include traffic (full load spectra for single, tandem, tridem, and quad axles), material and subgrade characterization, climatic factors, performance criteria, shoulders, subdrainage, joint details, and others. One of the most interesting aspects of the design procedure is the consideration of different levels of inputs. Level 1 requires the engineer to obtain the most accurate design inputs (e.g., direct testing of the materials, on-site WIM and AVC, etc.). Level 2 requires testing, but the use of correlations is allowed (for example, subgrade modulus estimated through correlation with another test), and Level 3 generally uses estimated values. Thus, Level 1 has the least possible error associated with inputs, Level 2 has more and Level 3 has the most. The effect of potential error on design reliability is directly considered in design. The basic assumptions used to structurally model the PCC slab, the base, the subbase and the subgrade along with joints are described in the paper. The primary finite element model used was the new finite element program, ISLAB2000. Factorials of ISLAB2000 runs were performed to train neural networks for rapid prediction of critical distresses. The key distress types include joint faulting, top-down slab cracking, and bottom-up slab cracking. Each was modeled using mechanistic principles and damage accumulated over the design life. Smoothness is characterized by the International Roughness Index (IRI) and is dependent on initial as-constructed IRI, the above distresses, and site conditions of subgrade and climate. The incremental damage approach used is perhaps the most significant aspect of the design procedure in that it allows for the direct consideration of changes in many factors throughout the entire design period, including material properties (PCC strength and modulus, erosion of base), seasonal climatic conditions, traffic loadings, joint load transfer, subgrade support, and others. Each analysis increment represents a specific combination of the preceding factors over a distinct period of time (i.e., month, season). 7th International Conference on Concrete Pavements — Orlando, Florida, USA — September 9-13, 2001 Reliability is directly considered through realistic simulation of the project design process and construction considering variabilities and uncertainties of each design factor and potential errors in models. Input estimation errors for Levels 1, 2, and 3 are directly considered. Monte Carlo simulation is used to develop probable distributions of each distress and IRI over the design period. Reliability is then defined as the probability that a given distress type or IRI will not exceed a critical limiting value. One of the most important aspects of the design procedure is the use of many pavement sections located throughout North America (various databases including LTPP) for calibration purposes. This process will reduce the distress and IRI prediction bias associated with the models.