Top-down cracking has become a commonly reported cracking mechanism in asphalt pavements worldwide. In top-down cracking, a crack initiates at the surface of an asphalt concrete pavement and propagates to the bottom of the asphalt pavement layer. Because the location and governing state of stress for top-down cracking are different from those for bottom-up cracking, analysis of pavement cracking performance must be robust enough to account for the complex mechanisms that are involved in top-down cracking. This study applies the viscoelastic continuum damage finite element model to the evaluation of two pavement sections in North Carolina where top-down cracking has been identified. Small specimen geometries are used to perform simplified viscoelastic continuum damage testing on individual asphalt layers obtained from field cores. This testing model and the Fourier finite element program are used together for pavement cracking performance simulations, and the joint model uses the structure and layer material properties obtained from the two study pavements. The simulation results clearly support the propensity of these pavements to exhibit top-down cracking. In addition to laboratory testing and analysis, the deflection-based method suggested by Uhlmeyer et al. is applied to the data obtained from pavement sections with known crack initiation locations, and that method's validity is investigated. The Uhlmeyer method uses the AREA parameter, which is determined from falling weight deflectometer deflections, and pavement thicknesses. The analysis results show a clear difference in the AREA versus pavement thickness relationship between the pavement sections with top-down cracking and those with full-depth cracking.
Presently, North Carolina is experiencing higher than anticipated rates of fatigue cracking. Field materials and pavement conditions are investigated to find the primary causes of cracking in North Carolina. This study finds that pavements with high asphalt content tend to be in good condition based on the top-down cracking (TDC) observed in the top layer, and pavements with low air void contents tend also to be in good condition. In addition, fine-graded mixes tend to yield a better pavement condition than coarse-graded mixes. The structure-related comprehensive analysis suggests that debonding is one of the major causes of a poor pavement condition. Road widening is another cause of cracking that can develop into fatigue cracking. Regions in which bottom-up cracking is observed tend to have larger bending strains at the bottom of the asphalt layer than regions where TDC is observed.
Objective: The purpose of this study is to select the methodology for SMR HRA which has characteristics that are different from existing nuclear power plants and digitalbased plants.
Background:We must assure safety to preoccupy export of technology to developing countries or countries interested in nuclear application. And we can be an advanced country in nuclear technology by securing original technology in the field of SMR such as SMART.Method: THERP, which is the most representative HRA methodology among all, and RARA, which is the latest HRA methodology. This study compared and evaluated THERP and RARA.Results: As a result of applying THERP and RARA methodologies which are based on LOCA EOG task analysis result, this research concluded that RARA has higher personal errors than THERP.
Conclusion:This study needs validation for LOCA, emergency operations, normal and abnormal scenarios since HRA methodology was only focused on LOCA scenario.
Application:The results of this study can apply as base line data when designing MMIS, which is the main control room of SMART, and when building a simulator.
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