所有的神话故事.:翻译英译汉

The anticipated 2002 AASHTO Guide for Design of New and Rehabilitated Pavement Structures will advance the state of the art over the WSDOT and MnDOT procedures on several key aspects, including the use of load spectra for traffic modeling, the use of finite-element (FE) analysis for response prediction in certain situations, and the incorporation of reliability in life-cycle cost assessment. However, because of its reliance on off-the-shelf models, the 2002 AASHTO Guide will probably only be a moderate step forward on the technology side. Its greatest benefit is that, as the new guide, it will likely add much more credibility to the use of M-E-based design than in the past.
KEY COMPONENTS
Following is a brief description of the key components that constitute the state-of-the-art
flexible pavement design procedure.
Analytical Models
A number of different types of models (mostly computer based) can be used to predict the state of stress in a pavement under simulated wheel and environmental loading conditions. The models that primarily fall into this category are those based on multilayer elastic (MLE) theory and FE analysis. The MLE models are considered satisfactory for predicting flexible pavement response under external wheel loads and are also relatively easy to operate, fast executing, and widely used. They are not capable of predicting pavement response associated with any environmental loading (i.e., that due to daily temperature changes, temperature gradients, moisture variations, etc.). FE models are also very good for predicting pavement response and are capable of considering both wheel and environmental loading. Unfortunately, they are complicated to operate and time-consuming, and therefore are not typically used for M-E flexible pavement design. Another emerging analytical modeling approach, fracture mechanics, may eventually find its way into future M-E design procedures.
Transfer Functions
A multitude of relationships have been developed to relate the state of stress in a pavement to its overall performance. In current M-E design procedures for flexible pavements, the primary transfer functions are those that relate (a) maximum wheel load tensile strain in the hot-mix asphalt (HMA) surface layer to eventual fatigue cracking and