This document constitutes the user manual for tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted by the University of California Pavement Research Center for the California Department of Transportation. tBeam is finite element based, employing multi-layered three-node Timoshenko beam elements resting on a viscoelastic Winkler foundation. It provides an approximation of the deflection bowl of pavements and the energy dissipated in pavement structures when subjected to loads moving at constant velocities. tBeam supports two loading options: a uniform pressure (per unit length) applied to a segment at the center of the beam, and a rolling rigid wheel. To achieve numerical efficiency the load-beam-foundation system is represented relative to a moving coordinate system attached to the moving load. The higher efficiency is made possible because, in this framework, an observer attached to the moving coordinate system perceives a “static” state (i.e., independent of time). The standalone tBeam software serves two purposes. First, to provide developers of pavement LCA tools a “guide” as to how to integrate tBeam technology into their program. To this end, the “main” of tBeam can be used as “guide” for integrating tBeam capabilities within the LCA tool. Second, tBeam capabilities are relevant to pavement research in general. Thus, it could represent a useful addition to the toolset for pavement viscoelastic mechanics.

One of the most important contributors to the environmental impacts from use of highways is the energy exerted by vehicles, particularly routes that carry higher volumes of traffic. Part of this energy is consumed by response of the vehicle’s tires and suspension to pavement surface roughness and macrotexture. Another part of the energy consumed is by energy dissipation due to the structural response of the pavement itself under the moving load. This document is the theoretical and validation manual tor tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted the University of California Pavement Research Center for the California Department of Transportation. The energy consumed due to structural response are controlled by the structural properties of the pavement which are dependent on the time of day, the season, and the condition (damage) of the pavement. The energy dissipation also depends on the speed and weight of each moving wheel load. As a result, estimating the lifetime energy dissipated in a pavement structure requires multiple analyses considering the thousands of permutations of these variables for a given segment of the highway network. Therefore, models for pavement-vehicle energy dissipation must balance two opposing needs: obtaining a reasonably accurate estimate of the dissipated energy, and high numerical efficiency. For numerical efficiency, the tBeam software employs a one-dimensional finite-element based solution of a wheel traveling at a constant velocity on a viscoelastic beam-foundation system, and a further reduction of numerical effort is obtained by formulating the model relative to a moving coordinate system attached to the wheel. The one-dimensional solution is, by nature, an approximation to the three-dimensional world. This approximation can be improved by incorporating a “correction factor,” which is based on comparisons with pavement simulations accounting for the double curvature observed in loaded pavements. In this report prediction disparity for a single structure is studied. The results show a clear trend where the correction factor decreases with rising temperature, and increases with higher velocity. The present study was insufficient to establish a law for the correction factor even for the single case studied. The correction factor ranged from about 1.25 at low temperature and high velocity to about 0.6 for high temperature and low velocity. The first part of this report presents the underlying theory for tBeam and implementation details. The second part presents closed form solutions for specialized pavement-foundation systems. The third component of the report presents some of the validation simulations undertaken to demonstrate the performance of tBeam, including comparisons with closed form solutions provided in this report, and recommendations for further development of tBeam.

Bus Rapid Transit (BRT) has the potential to improve mass transit service and contribute to reduced traffic congestion in urban areas. To achieve this improvement in service BRT will require the use of dedicated bus lanes together with lane assist and precision docking (LA/PD) to accelerate the passenger boarding process. Using this approach, BRT lanes can be reduced somewhat in width. However, such a reduction will result in increased channelization of traffic which in turn can lead to a more rapid development of pavement distress. With today’s improved pavement engineering technology, it is possible to design and construct pavement infrastructure which can result in long term and cost effective pavement performance (both in terms of pavement deterioration and equipment wear and tear). At the same time the system can be environmentally friendly with reduced traffic noise and increased passenger comfort from a smoother ride.