Ibrahim Janajreh

Flexible pavement responses to different loading amplitudes considering layer interface condition and lateral shear forces

A three-dimensional (3D) finite element (FE) parametric study was conducted to quantify the viscoelastic pavement responses due to different tire configurations: dual and wide-base tires, at three temperatures (5, 25 and 40°C) and two speeds (8 and 72 km/h). Three factors affecting pavement responses were investigated: type of moving wheel loading amplitude (continuous, trapezoidal), interface layer condition (simple-friction and elastic-stick models) and lateral surface forces. It was found that the continuous loading amplitude, which has an asymmetric stress magnitude and considers the difference between the entrance and exit of the tire, can simulate pavement responses to moving wheel vehicular loading more accurately than the currently used trapezoidal loading amplitude. The elastic-stick model resulted in a sensible improvement for predicting pavement responses to dual tire, while the simple-friction model is more comparable to field measurements in the case of the wide-base tire. The shear force was found to positively improve the prediction of the calculated strain at the bottom of the wearing surface and to a lesser degree at the bottom of the hot mix asphalt (HMA) base layer. This study concludes that using continuous loading amplitude and non-uniform pressure distribution to simulate a moving wheel, surface shear forces and appropriate layer interface friction may significantly improve the capability of FE models to predict pavement response to vehicular loading. Results have been successfully validated against field measurements.

Pavement response to dual tires and new wide-base tires at same tire pressure

Although concern was raised about the introduction of radial tires due to their higher inflation pressure compared with that of bias tires, radial tires have been proven to reduce the strain at the bottom of the hot-mix asphalt (HMA) layer. However, conventional wide-base single tires have been shown to be more damaging to pavement than dual tires. The damage mainly depends on the tire tread width and inflation pressure. It has been suggested that wide-base tires may produce damage equivalent to that of dual tires if the maximum load per tire is limited to 11.6 kg/mm of tire tread width. Recent advances in tire design and material have led to the design of a new wide-base tire that is wider and flatter in the crown area to provide a uniform contact stress distribution. It operates at an inflation pressure of 690 kPa for 151-kN tandem axle load. An experimental program studied the effects of the newly developed wide-base tire on a flexible pavement section at the Virginia Smart Road under different loading and environmental conditions. Testing results have shown that the newly developed wide-base tires induce approximately the same horizontal tensile strains under the HMA layer as do equivalent dual tires. Hence, the fatigue damage expected from these newly developed wide-base tires is the same as that produced by dual tires. However, the vertical compressive stresses induced by the wide-base tire are greater on the upper HMA layers of the pavement. The difference in stresses diminishes with depth and becomes negligible at the bottom of the subbase layer.

Quantification of Pavement Damage Caused by Dual and Wide-Base Tires

A study conducted in 2001 on the heavily instrumented Virginia Smart Road measured pavement responses to a new generation of single wide-base tire (445/50R22.5) and to dual tires (275/80R22.5). The new single wide-base tire has a wider tread and a greater load-carrying capacity than conventional wide-base tires. The potential fatigue damage resulting from different tire configurations was evaluated. After successful field testing, a finite element (FE) parametric study was conducted to investigate different failure mechanisms that were not evaluated in the field. In this study, dual tires and two new generations of wide-base tires (445/50R22.5 and 455/55R22.5) were evaluated. The main difference between the two generations of wide-base tires is that the 455/55R22.5 is wider than the 445/50R22.5; hence, it further reduces the contact stress at the pavement surface under the same nominal tire pressure. In the developed FE models, geometry and dimensions were selected to simulate accurately the axle configurations typically used in North America; actual tire tread sizes and applicable contact pressure for each tread were considered; laboratory-measured pavement material properties were incorporated; and models were calibrated and properly validated against stress and strain measurements obtained from the experimental program. Four failure mechanisms were considered: fatigue cracking, primary rutting, secondary rutting, and top-down cracking. Results indicated that the new generations of wide-base tire would cause the same or relatively greater pavement damage than conventional dual tires. Because overall truck weight is reduced by approximately 450 kg when wide-base tires are used, it is reasonable to implement the load limits currently applied to the dual-tire assembly on the 455/55R22.5 wide-base tire.

Effects of Tire and Vehicle Design Characteristics on Rollover of Tractor Semi-Trailers

Understanding the effects of tire and vehicle properties on the rollover propensity of tractor semi-trailer trucks is essential. The major objective of the project described by this paper was to develop a simplified computational tool that can be used to understand and predict the effects of various tire characteristics and truck design parameters on rollover under steady cornering and non-tripped conditions. In particular, this tool may be used to help understand the basic me hanisms governing rollover propensity of trucks equipped with New Generation Wide Single tires as contrasted with conventional tires. Effects of tire flexibility, roll-compliant suspensions, fifth -wheel lash and nonlinear suspension characteristics are included in the model and are presented below. Design parameter data used as input to the model were obtained from Michelin Americas Research and Development Corporation. Results have shown that changing from dual tires to New Generation Wide Single tires increases the rollover threshold by approximately 3%.

Ride Dynamics and Pavement Loading of Tractor Semi-Trailers on Randomly Rough Roads

An investigation of the vertical dynamics of a tractor semi-trailer traversing a random road profile was conducted. This paper presents the development of a 14 degree-of-freedom (DOF), dynamic ride model of a tractor semi-trailer. It is based on work previously conducted by Vaduri and Law [1] and Law et al [2]. The DOFs include: (a) vertical displacements of each of the five axles, the tractor frame, the engine on its mounts, the cab on its suspension, and the drivers seat; (b) pitch displacements of the trailer with respect to the tractor, the cab, and the rigid tractor frame; and, (c) the first bending or beaming modes of the tractor and trailer frames. The model also incorporates suspension friction, and tire non-uniformities. The simulation of the model is conducted using MATLAB software. Further, the model is used to examine the effects on ride and pavement loading of wide-base and conventional tires, suspension friction, tractor and trailer beaming, and statistical variations in parameters such as tire pressure, axle suspension stiffness, etc.

Optimization to Improve Lateral Stability of Tractor Semi-Trailers During Steady State Cornering

Decreasing the propensity for rollover during steady state cornering of tractor semi-trailers is a key advantage to the trucking industry. This will be referred to as increasing the lateral stability during steady state cornering and may be accomplished by changes in design and loading variables which influence the behavior of a vehicle. To better understand the effects of such changes, a computer program was written to optimize certain design variables and thus maximize the lateral acceleration where an incipient loss of lateral stability occurs. The vehicle model used in the present investigation extends that developed by Law [1] and presented in Law and Janajreh [2]. The original model included the effects of tire flexibility, nonlinear roll-compliant suspensions, and fifth wheel lash. This model was modified to include (a) additional effects of displacement due to both lateral and vertical tire flexibility, and (b) provisions for determining off-tracking. This improved model was used as a basis for an optimization routine that initially maximizes the payload capacity, subject to legal peraxle load constraints, by determining an optimum set of tractor and semi-trailer adjustments in the placement of the fifth wheel and the trailer axles. After this initial step, an optimization routine is implemented which maximizes the rollover indicator, a practical measure of rollover propensity. The rollover indicator is calculated as an average of two components including (a) the minimum acceleration for which there is no valid solution to the equations of equilibrium (or critical lateral acceleration) where rollover is imminent and (b) the acceleration at which inside wheel lift-off first occurs. The rollover indicator is maximized in the optimization routine by the choice of appropriate values of various design variables. These include load placement, tire stiffness, vehicle track, and others. The tractor semi-trailer considered in the optimization was equipped with new single tires. Michelin Americas Research and Development Corporation provided parameter data for the vehicle.

Pavement Damage Due to Conventional and New Generation of Wide‐Base Super Single Tires

Abstract The objective of this study was to quantify pavement damage due to a conventional (385/65R22.5) and a new generation of wide‐base (445/50R22.5) tires using three‐dimensional (3D) finite element (FE) analysis. The investigated new generation of wide‐base tires has wider treads and greater load‐carrying capacity than the conventional wide‐base tire. In addition, the contact patch is less sensitive to loading and is especially designed to operate at 690kPa inflation pressure at 121km/hr speed for full load of 151kN tandem axle. The developed FE models simulated the tread sizes and applicable contact pressure for each tread and utilized laboratory‐measured pavement material properties. In addition, the models were calibrated and properly validated using field‐measured stresses and strains. Comparison was established between the two wide‐base tire types and the dual‐tire assembly. Results indicated that the 445/50R22.5 wide‐base tire would cause more fatigue damage, approximately the same rutting dama...

Effects of Tractor and Trailer Torsional Compliance and Fill Level of Tanker Trailers on Rollover Propensity During Steady Cornering

Understanding the parameters which influence the tendency for a heavy truck to exhibit rollover is of paramount importance to the trucking industry. Multiple parameters influence the vehicles motion, and the ability to determine how each affects the vehicle as a system would be an indispensable tool for the design of such vehicles. To be able to perform such predictions and analysis, models and a computer simulation were created to allow the examination of changes in design parameters in such vehicles. The vehicle model was originally developed by Law [1] and presented in Law and Janajreh [2]. The model was extended further by Lawson [3, 4] to include (a) the effects of the torsional compliance of both the tractor and trailer, and (b) tanker trailers with various levels of liquid fill. In the present paper, both the tractor and trailer compliances were studied independently to determine their influences on the rollover stability of the vehicle. Additionally, rollover characteristics of tankers having a range of fill levels were analyzed.

Truck rollover characterization for class-8 tractor-trailers utilizing standard dual tires and new-generation single tires

OVERVIEW The Heavy Truck Rollover Characterization Project is a USDOT-sponsored research effort conducted through its University Transportation Centers (UTCs) Program through the National Transportation Research Center, Inc. (NTRCI), located in Knoxville, Tennessee. The research is being conducted by the Oak Ridge National Laboratory (ORNL) in partnership with Michelin Americas Research and Development Corporation (Michelin), Western Michigan University, Battelle, Volvo Trucks North America, Clemson University and Dana Corporation. The long term fivephase project will: (1) contribute to the understanding of the dynamics of heavy truck rollover; (2) contribute to the development of advanced models of heavy truck vehicle dynamics that reflect project experiences, and (3) develop recommendations for improvement of the roll stability of heavy vehicles and testing such realizations in an integrated tractortrailer concept. The five phases include: Phase 1 Tractor-Box-Trailer Characterization with Standard Dual Tires; Phase 2 Tractor-Box-Trailer Characterization with New Generation Single Wide-Based Tires (NGSWBTs) and a wider-slider trailer suspension; Phase A Tractor-Flat-Bed Trailer with standard dual tires, NGSWBTs, and Electronic Stability Control; Phase B Tractor-Tanker with technologies yet to be determined; and Phase C Development of an Integrated Tractor-Trailer Concept building on the lessons learned from the previous four phases – the SafeTruck Concept.