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Mensagem por Manuela » 05 Set 2016, 14:17

Autores: Jerry G. Rose, Brett Malloy e Reginald R. Souleyrette.

Proceedings of the 2014 Joint Rail Conference
April 2-4, 2014, Colorado Springs, CO, USA

Rehabilitating and/or replacement of highway-railway at- grade crossings frequently accounts for major track maintenance expenses for the U.S. highway governmental agencies and the railroad industry. Substantial numbers of crossings deteriorate at a more rapid rate than the abutting trackbed and pavement. This is largely due to the structural implications of the combined highway and railway loadings within the jointly used crossing area and difficultly in maintaining adequate drainage within the immediate crossing area.
A highway-railway at-grade crossing is designed to fulfill its primary purpose of providing a smooth surface for the safe passage of rubber-tired vehicles across the railroad. The jointly used area represents a significantly expensive unit cost of the highway and railway line. Ideally a highway crossing will maintain a smooth surface and stable trackbed for a long period of time. This reduces costly and frequent disruptions to highway and railway traffic when the track needs adjusting or the surface needs replacing due to rideability concerns. Technology is available for “fast-tracking” the renewal of highway crossings within one day (if desired) using a panel system with specifically designed layered support and premium materials. The procedure involves complete removal of the old crossing panel and trackbed materials. The replacement consists of an asphalt underlayment layer, a pre-compacted ballast layer, a new track panel, and a new crossing surface. The composition of the asphalt layer is similar to that used for highways. It replaces all, or a portion of, the typical granular subballast layer.
A cooperative effort between the local highway agency and the railway company will ideally reduce costs, improve the
quality of the finished product, and reduce outage of the highway and railroad during the rehabilitation process. A major objective is to minimize disruption to both highway and railway traffic during the renewal process in addition to improving the performance and extending the life of the crossing. Typical schedules are for the railroad to be out-of- service for a maximum of four hours and for the highway to be closed only eight to twelve hours, when length of closure is an issue of importance.
Numerous long-term tests and performance evaluations of heavy trafficked railway and highway crossings are presented herein. Pressure cells have been imbedded within the trackbed to document pressure levels within the layered portion of the crossing structure due to loadings from trains and highway vehicles. In addition, long-term settlement measurements and assessments for several crossings are documented. The measurements indicate significantly reduced long-term settlements of crossings incorporating the rapid-renewal, layered system, while maintaining acceptable smoothness levels. In addition, standard practices and specifications are presented for several highway agencies and railway companies using this technology for their crossing renewal programs. These long-term performance evaluations indicate this practice ensures long-life, economical, smooth crossings for improved safety and operating performances. The application of this technology continues to increase and it is considered a standard practice in many areas of the country.
A crossing management technique (model decision-making process) is described for assessing the optimum engineering solutions to restore desired smoothness, minimize subsequent settlement, and ensure acceptable long-term performances for highway-railway at-grade crossings. These are site-specific and based on historical performance, the present observed performance and condition, and measurable parameters for the particular crossing.
The model decision-making process includes three options, depending on the source(s) of the crossing roughness. The process can involve merely making improvements to the quality of the pavement approaches. Another scenario can be to replace only the deteriorated crossing surface. The most involved solution is the complete renewal of the crossing surface, track panel, and underlying support to rectify a chronic problem that may be inhibiting the crossing from achieving optimum performance.
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