Zoltan Rado

Exploring the texture–friction relationship: from texture empirical decomposition to pavement friction

This paper investigates the pavement friction–texture relationship, using a decomposition method of the pavement texture that is part of a new signal processing technique called ‘Hilbert–Huang transform’ to develop a texture parameters–friction relation. This method allows the empirical decomposition of the texture profile to a set of basic profiles in a limited number, called ‘intrinsic mode functions’ or IMFs. From the obtained IMFs, a set of four new functions called ‘base intrinsic mode functions’ or BIMFs, are introduced and are characterised from the density and sharpness of the peaks contained in the individual BIMFs. Then these two parameters are correlated with the pavement friction using different combinations. This procedure is applied to a set of texture and friction data measured through test roads in France. The textures and frictions are measured using, respectively, the Circular Texture Meter and the Dynamic Friction Tester in France and also on a number of test sites in the USA. The obtained results show a good correlation between some of the BIMF parameters (density and sharpness) and friction.

Field Tests and Numerical Modeling of Vehicle Impacts on a Boulder Embedded in Compacted Fill

Landscape Vehicular Anti-Ram (LVAR) systems are a group of protective barriers, which are designed using natural materials (e.g., boulders) and have proven to both effectively protect sensitive structures against threats and be aesthetically pleasing. This paper presents two consecutive vehicular crash tests hitting the same single boulder embedded in AASHTO coarse aggregate fill. A LS-DYNA model was developed to simulate the field-scale tests, which were instrumented with high-speed cameras and pressure cells. A readily available truck model from the National Crash Analysis Center was modified and implemented in the LS-DYNA model. The boulder and surrounding soil were modeled using the Mohr-Coulomb failure criteria. The model parameters were calibrated using results from the first field-scale test with a truck traveling at 48.3 km/hr (30 mph) impacting the LVAR system. The calibrated model was then used to simulate the second field-scale test, which involved a truck traveling at 80.5 km/hr (50 mph) impacting the same LVAR system without resetting the boulder or soil. The calibrated model was able to provide the global response of the system, including the time-history of the translational displacement and rotation of the boulder, and was in good agreement with field-scale test results. This suggests that the overall global response was dominated by the dynamic behavior of the truck and boulder system upon impact. Hence, a simple material model for soil and boulder is sufficient for simulating the tests conducted.

Contribution to pavement friction modelling: an introduction of the wetting effect

ABSTRACT This paper presents a friction model describing the tyre rubber/road interaction that takes into account the viscoelasticity of the tyre rubber, the texture of the road surface and a water layer between the tyre/road interface by introducing explicitly a computation of the water layer effect in the calculation process of the hysteretic friction. The geometry of the wetted portion of the interface model is simplified by transforming it into an equivalent hydrodynamic bearing. Utilising the Reynolds equation, the bearing load capacity is calculated and the resulting forces are subtracted from the contact load when calculating the forces of the hysteretic friction. The mechanical behaviour of the rubber is represented in the model by Kelvin–Voigt model. The frictional forces due to hysteresis are calculated at any given operating conditions (load, slip speed, etc.) from the contact geometry of rough surfaces caused by the viscoelastic behaviour of rubber. To validate the model, a set of surfaces including real pavements and artificially textured slabs were selected covering a wide range of microtexture and macrotexture combinations and the computed and measured friction compared. To describe the contact geometry of rough surfaces using macrotexture and to measure actual friction, the Circular Track Meter and the Dynamic Friction Tester devices were used, respectively. The friction coefficients computed using the model were compared to the measured friction coefficients. The obtained results are presented in the paper and proved to provide high correlation between the measured and modelled friction. The model is capable to predict wet friction at low as well as high speeds on wet surfaces, thus proving to be capable to take adequately the wetting effect on the variation of friction with increasing speed. Recommendations are provided to improve the model and extend it to a tyre friction model.

Field test and numerical modeling of vehicle impact on a boulder with impact-induced fractures

Landscape Vehicle Anti-Ram systems, typically comprising natural materials such as boulders, are effective in protecting sensitive structures against threats. However, fracturing of these materials under vehicular impact can be detrimental to the performance of Landscape Vehicle Anti-Ram systems. This study presents a field-scale crash test and LS-DYNA modeling of a Landscape Vehicle Anti-Ram system subjected to vehicular impact. The Landscape Vehicle Anti-Ram system consisted of three boulders connected through a reinforced concrete foundation embedded in compacted American Association of State Highway and Transportation Officials soil. The central boulder fractured upon vehicular impact. An advanced material model was adopted to model the rock fracture and crushing. The global response of the truck, including cab deformation and dynamic penetration, from the simulation showed good agreement with the field observations. The failure patterns of the boulder, including the fracture plane and minor crushing, also agreed well with the field observations. Through a parametric study, the dynamic penetration of the truck is found to be influenced by the elastic modulus and fracture energy of the boulder, and the Landscape Vehicle Anti-Ram system is more effective with a stiffer and tougher boulder.

Computational and experimental modification of portable sign structure design following NCHRP 350 criteria

As a follow-up to a study published in 2008 [J.-W. Seo, D.G. Linzell, and Z. Rado, Crash performance of x-shaped support base work zone temporary sign structures, Int. J. Crashworthiness 13 (2008), pp. 437–450], research discussed herein examines effective methods for selecting and modifying portable sign structure designs so that they are deemed acceptable according to National Cooperative Highway Research Program (NCHRP) Report 350 [H.E. Ross, Jr., D.L. Sicking, J.D. Zimmer, and R.A. Michle, Recommended procedures for the safety performance evaluation of highway features, National Cooperative Highway Research Program Rep. 350, Publication Project 22–7 FY’89, Texas Transportation Institute, Austin, TX, 1993] criteria. Portable sign structures, often used as signage for work zones, are frequently susceptible to vehicular impact. If an impact occurs, a possible safety threat to occupants in the vehicle exists due to sign panel penetration. In this study, the methodology used to select a portable sign structure design from two alternatives, one of which was summarised in the 2008 publication [J.-W. Seo, D.G. Linzell, and Z. Rado, Crash performance of x-shaped support base work zone temporary sign structures, Int. J. Crashworthiness 13 (2008), pp. 437–450], is presented along with the procedure used to optimise the selected design so that it performed acceptably according to the NCHRP 350 standards. The selected design, one having an H-base, was modified to meet the NCHRP 350 criteria by strategically replacing traditional metallic fasteners with nylon fasteners. Procedures used to simulate the impact tests, select the appropriate base design and modify that design to meet the NCHRP criteria are presented.

Field testing and numerical investigation of streetscape vehicular anti-ram barriers under vehicular impact using FEM-only and coupled FEM-SPH simulations

This article presents two field-scale crash tests of Streetscape Vehicle Anti-Ram barrier systems and LS-DYNA simulations to predict the global response of each system under vehicular impact. Tests 1 and 2 consisted of a five-post welded bus stop and a welded bollard, respectively; both were in a steel and concrete composite foundation embedded in compacted American Association of State Highway and Transportation Officials aggregate. Test 1 resulted in a P1 rating, where minimal foundation uplift and rotation were observed. Test 2 failed to result in a P1 rating, where significant foundation uplift, rotation, concrete cracking, and large deformation of surrounding soil were observed. For each test, two LS-DYNA models, namely, a finite element method–only model and a hybrid finite element method–smoothed particle hydrodynamics model, were created to predict the global response of the system. In the finite element method–only model, traditional finite element method approach was used for the entire soil region; in the hybrid finite element method–smoothed particle hydrodynamics model, the near-field soil region was modeled using the smoothed particle hydrodynamics approach, whereas the far-field soil region was modeled using the finite element method approach. For Test 1, both the finite element method–only model and the hybrid finite element method–smoothed particle hydrodynamics model were able to match the recorded global response of the system. For Test 2, however, the finite element method–only approach was not able to accurately predict the global response of the system; on the other hand, the hybrid finite element method–smoothed particle hydrodynamics approach was able to capture the global response including the bollard pullout, soil upheaval, and vehicle override. This research suggests that the hybrid finite element method–smoothed particle hydrodynamics approach is more appropriate in simulating the field performance of embedded structures under impact loading when large deformation of the surrounding soil is expected.

Field-scale testing and numerical investigation of soil-boulder interaction under vehicular impact using FEM and coupled FEM-SPH formulations

A computational approach that couples the Finite Element Method and the Smoothed Particle Hydrodynamics method may be advantageous for simulating the response of complex, physical systems involving large deformations. However, comparisons of this modeling technique against field-scale test data are remarkably sparse in literature. This study presents three field-scale tests involving vehicular impact into three landscape vehicular anti-ram barriers. Each barrier consisted of a single boulder embedded in compacted American Association of State Highway and Transportation Officials soil and physical testing resulted in one of the following outcomes: minimal boulder/soil movement (Test 1), moderate boulder/soil movement (Test 2), and severe boulder/soil movement and vehicle override (Test 3). For each test, two LS-DYNA models were developed: a model using a traditional finite element method approach for the entire soil region along with a model using a hybrid finite element method-smoothed particle hydrodynamics approach where the near-field soil region was simulated using smoothed particle hydrodynamics. For Tests 1 and 2, both the traditional finite element method approach and the hybrid finite element method-smoothed particle hydrodynamics approach were able to accurately match data collected from the field tests. However, for Test 3, the finite element method-only approach was not able to accurately predict the global response of the system under vehicular impact. On the other hand, the hybrid finite element method-smoothed particle hydrodynamics approach was able to capture global response of the system including boulder rotation, soil upheaval, and vehicle override.

Crash performance of X-shaped support base work zone temporary sign structures

Results from numerical analyses of temporary sign structure crash tests are compared with test data to assess both their crashworthiness and numerical model effectiveness. In addition, a parametric study is performed to investigate the influence of various parameters that would affect crash performance. Sign structures supported with an X-shaped base configuration in plan (‘X-base’) were examined, with all tests being performed following National Cooperative Highway Research Program (NCHRP) 350, ‘Recommended Procedures for the Safety Performance Evaluation of Highway Features’ guidelines [16]. Simulations and tests were completed at a speed of 98.7 km/h (61.3 mph) as directed by NCHRP 350 with the signs oriented perpendicular and parallel to the vehicles direction of travel. Results from the study indicated that numerical simulations properly predicted the crash behaviour. In addition, both the numerical model and crash tests showed that orienting the X-base structure parallel to the vehicle direction would result in sign penetration into the vehicle compartment and, subsequently, an unsatisfactory condition according to NCHRP 350.