Identifying the Effects of Soil and Climate Types on Seasonal Variation of Pavement Roughness Using MML Inference

Pavement roughness is a common measure of pavement distress and one regularly measured by road authorities. While permanent pavement deterioration that equates to increased roughness is commonly modeled, cyclical or seasonal variations are often not included. While these variations may be small, they may be important when alternate pavements are compared directly for performance. We propose that seasonal variation may be described by partitioning the data into groups that are modeled as a segmentation problem. We developed a minimum message length (MML) segmentation tree (MMLST) criterion for partitioning and segmentation of the data. We performed simulated comparisons comparing common segmentation criterion (MMLST, maximum likelihood, Akaike information criterion, and Bayesian information criterion) and conclude that MMLST is the preferred criterion. MMLST assists in answering the following questions. First, is the observed segmentation pattern due to seasonal variation or merely random scatter? Second, given evidence of seasonal variation, what type of segmentation pattern should model these trends? Furthermore, does the interaction of climatic and soil conditions appear to affect this variation?     

Live Load Distribution in Girder Bridges Subject to Oversized Trucks

A significant challenge facing motor carriers and engineers in this nation is the limitation of vehicle size and weight based on pavement and bridge capacity. However, the current demands of society and industry occasionally require a truck to carry a load that exceeds the size and weight of the legal limit. In these cases, engineering analysis is required before a permit is issued to ensure the safety of the structures and roadways on the vehicle's route. A truck with a wheel gauge larger than the standard 1.83 m (6 ft) gauge requires additional engineering effort because the wheel load girder distribution factors (GDFs) established by AASHTO cannot be used to accurately estimate the live load in the girders. In this study, the finite-element method is used to develop modification factors for the AASHTO flexure and shear GDFs to account for oversized trucks. The results of the analysis showed that the use of the proposed modification factors with the specification-based GDFs can help increase the allowable loads on slab-on-girder bridges.     

Dynamic Response Solution in Transient State of Viscoelastic Road under Moving Load and Its Application

In order to study the dynamic response of an asphalt road, a dynamic model of the road under a moving load is proposed, in which the viscoelastic characteristics of the base and pavement are all considered, the pavement is regarded as an infinite beam on a Kelvin viscoelastic base. By using Green’s functions, Laplace transforms, and Fourier transforms, the analytical solution in transient is deduced. As the viscosity of the pavement is included in the model, the analytical solution can be used to investigate more of the factors that affect the dynamic response, such as vehicle speed, temperature, and road material properties. Using this analytical solution, some numerical calculations are given to illustrate the effects of vehicles’ speeds and different damping on the deflection with the displacement.     

Effect of Stress‐Dependent Base Layer on the Superposition of Flexible Pavement Solutions

Flexible pavement structural analysis for design usage must consider (as a minimum) multiple wheel/axle loading configurations, seasonal variations of material layer properties, and the nonlinear behavior of unbound materials. Although these requirements are all easily within the capabilities of three‐dimensional finite element analysis, the required computation times may be impracticably long for routine design. Compromises between analytical rigor (e.g., three‐dimensionality) and analysis features (e.g., multiple wheels, seasonal property variations, material nonlinearity) must be made. One compromise is to retain seasonal property variations and material nonlinearity within an axisymmetric single wheel finite element model and to approximate multiple wheel effects via superposition. Although this superposition of nonlinear solutions is undeniably invalid from a rigorous theoretical viewpoint, the errors may be well within acceptable magnitudes for practical design. The paper investigates this issue by comparing superimposed nonlinear solutions against computationally rigorous three‐dimensional nonlinear solutions and evaluating the discrepancies in key pavement response quantities. The results suggest that the errors from superimposing nonlinear solutions are acceptably small for key pavement response quantities. Moreover, these errors are substantially smaller than those resulting from neglect of nonlinear unbound material behavior, a modeling compromise that is common in pavement structural analysis today.     

Prediction of Temperature and Moisture Changes in Pavement Structures

Although the effects of climate on pavement structures are recognized as major contributors to the deterioration of pavement structures in cold regions, only a few models concerned with both frost heave and thaw settlement have been developed. In this study, a coupled mass and heat transfer model, FROSTB, developed by the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) was tested and evaluated with respect to parameters critical to thaw weakening. With the main focus on soil moisture and temperature, the results were compared with data from an instrumented test road. The results indicate the soil temperature is predicted very well and soil moisture relatively well during freezing and thawing. Although a time lag was observed between observed and predicted start of thaw, the results suggest that the FROSTB model may serve as a good tool for many engineering purposes involving the freezing and thawing of pavement structures in cold regions.     

Experimental Evaluation of Dynamic Effects for a Selected Highway Bridge

The paper presents an experimental study of the actual dynamic effects for a preselected typical highway bridge. Knowledge of the dynamic impact factors is important for accurate determination of the ultimate load capacity and performance assessment of constructed bridges. Static and dynamic field tests were performed on a two-lane concrete highway bridge built in 1999 on U.S. 90 in northwest Florida. During the tests, one or two fully loaded trucks crossed over the bridge, which was instrumented with strain gauges, accelerometers, and displacement transducers. A wooden plank was placed across the lanes for some runs to trigger extensive dynamic vibration and to simulate poor road surface conditions. Data collected from the tests were used for comprehensive assessment of the bridge under dynamic loading. Impact factors obtained from the tests with higher speeds were found larger than corresponding values recommended by bridge codes. Analysis revealed that stiff vehicle suspension, road surface imperfection, and “bouncing” of the truck loading contributed to the high impact factors. Experimental data were also used for validation of the finite-element models developed for the vehicle–bridge system.     

Multigrid Preconditioner for Unstructured Nonlinear 3D FE Models

Multigrid and multigrid-preconditioned conjugate-gradient solution techniques applicable for unstructured 3D finite-element models that may involve sharp discontinuities in material properties, multiple element types, and contact nonlinearities are developed. Their development is driven by the desire to efficiently solve models of rigid pavement systems that require explicit modeling of spatially varying and discontinuous material properties, bending elements meshed with solid elements, and separation between the slab and subgrade. General definitions for restriction and interpolation operators applicable to models composed of multiple, displacement-based isoparametric finite-element types are proposed. Related operations are used to generate coarse mesh element properties at integration points, allowing coarse-level coefficient matrices to be computed by a simple assembly of element stiffness matrices. The proposed strategy is shown to be effective on problems involving spatially varying material properties, even in the presence of large variations within coarse mesh elements. Techniques for solving problems with nodal contact nonlinearities using the proposed multigrid methods are also described. The performance of the multigrid methods is assessed for model problems incorporating irregular meshes and spatially varying material properties, and for a model of two rigid pavement slabs subjected to thermal and axle loading that incorporates nodal contact conditions and both solid and bending elements.     

Dynamic Behavior of Deck Slabs of Concrete Road Bridges

This paper treats the dynamic effect of traffic actions on the deck slabs of concrete road bridges using the finite-element method. All the important parameters that influence bridge-vehicle interaction are studied with a systematic approach. An advanced numerical model is described and the results of a parametric study are presented. The results suggest that vehicle speed is less important than vehicle mass and that road roughness is the most important parameter affecting the dynamic behavior of deck slabs. The type of bridge cross section was not found to have a significant influence on deck slab behavior. The dynamic amplification factor varied between 1.0 and 1.55 for the bridges and vehicles studied. These results should be validated by further work.     

Noise Evaluation for Pavement Maintenance in Metropolitan Highway Bridges

Dynamic response of a bridge under traffic load induces acoustic energy at the bridge surface. The acoustic energy change generates an additional coupled noise component caused by vibration of a bridge deck associated with the pavement conditions and moving velocity of the vehicle. This paper presents a three-dimensional finite-element method developed for the dynamic response and noise propagation model, and analyzes the coupled effect induced by traffic loading based on different pavement conditions. Even though vibration-induced noise at the bridge is below the audible frequency range of 20–20,000?Hz, it amplifies the traffic noise source to the highly annoyed level of noise in the metropolitan area. Among several factors that contribute to the traffic noise, interaction between pavement and vehicle is considered according to the different surface roughness and vehicle velocity. The result shows that poor pavement condition contributes to the increase of traffic noise at a high traveling speed of the vehicle. In the pavement maintenance stage, the coupled effect as an additional noise source should be considered to mitigate the traffic noise for its added value in conjunction with regulation of engine emission noise and construction of a noise barrier.     

Validation of a Source–Receiver Model for Road Traffic-Induced Vibrations in Buildings. I: Source Model

This work focuses on the coupling of a validated source model for free field traffic-induced vibrations to a receiver model that enables one to predict the response of buildings, accounting for dynamic soil–structure interaction. The resulting model is validated by means of in situ measurements, that have been performed in and around a single-family dwelling during the passage of a truck with known characteristics at speeds between 23?km/h and 58?km/h on joints between plates of the concrete pavement and on a plywood unevenness installed on the road. Simultaneous vibration measurements have been performed with a mobile data acquisition system on the truck’s axles. The objective of part I of this paper is to present the validation of the source model. The characteristics of the vehicle and the road unevenness are discussed, and the vehicle response is validated. The response is independent of the vehicle speed for the passage on the joints, whereas, for the passage on the plywood unevenness, the vibrations increase with the vehicle speed. The dynamic road–soil interaction problem is subsequently solved. Special consideration is given to the determination of the dynamic soil characteristics using the spectral analysis surface wave and seismic cone penetration test methods and to the validation of the transfer functions in the soil. The free-field incident wave field is finally validated. This incident wave field is used in part II of the paper to predict and validate the response of the single family dwelling.     

Modeling Measured 3D Tire Contact Stresses in a Viscoelastic FE Pavement Model

Three‐dimensional (3D) contact stresses occurring between the road surface and the tire that were measured with the South African Vehicle Road Surface Pressure Transducer Array (VRSPTA) device under a moving wheel are transformed to a corresponding force/stress pattern representing the actual contact stress state under the tire by means of a software program. In combination with a dynamic load function such force patterns derived from these Stress‐in‐Motion (SIM) measurements with the VRSPTA device are used to introduce a more advanced load representation of the tire‐pavement interface into a three‐dimensional (3D) finite element (FE) model. Further, a method is presented to derive viscoelastic material properties of asphalt concrete (AC) mixes from dynamic frequency sweep shear (FS‐S) tests of lab specimens or field cores that can be used to define material behavior of the AC layers in the 3D FE pavement model. Linear elastic layered theory is utilized to validate the results of the FE computations in order to demonstrate that the FE method can successfully be used to include SIM measurements for more advanced analysis and design of pavements. First results of the 3D FE simulation of a load circle of the Heavy Vehicle Simulator (HVS) during accelerated pavement testing of a pavement test section are presented. These results encourage employment of the FE pavement model for further simulation work to assess the rutting potential of AC mixes in combination with different tire types and loading situations.     

Shakedown Approaches to Rut Depth Prediction in Low-Volume Roads

Rutting, due to permanent deformations of unbound materials, is one of the principal damage modes of low traffic pavements. Flexible pavement design methods remain empirical; they do not take into account the inelastic behavior of pavement materials and do not predict the rutting under cyclic loading. A finite-element program, based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings, has been used to estimate the permanent deformations of unbound granular materials subjected to traffic loading. Based on repeated load triaxial tests, a general procedure has been developed for the determination of the material parameters of the constitutive model. Finally, the results of a finite-element modeling of the long-term behavior of a flexible pavement with the simplified method are presented and compared to the results of a full-scale flexible pavement experiment performed by Laboratoire Central des Ponts et Chaussées. Finally, the calculation of the rut depth evolution with time is carried out.     

Live-Load Distribution Factors in Prestressed Concrete Girder Bridges

This paper presents an evaluation of flexural live-load distribution factors for a series of three-span prestressed concrete girder bridges. The response of one bridge, measured during a static live-load test, was used to evaluate the reliability of a finite-element model scheme. Twenty-four variations of this model were then used to evaluate the procedures for computing flexural live-load distribution factors that are embodied in three bridge design codes. The finite-element models were also used to investigate the effects that lifts, intermediate diaphragms, end diaphragms, continuity, skew angle, and load type have on distribution factors. For geometries similar to those considered in the development of the American Association of State Highway and Transportation Officials Load and Resistance Factor Design Specifications, the distribution factors computed with the finite-element models were within 6% of the code values. However, for the geometry of the bridge that was tested, the discrepancy was 28%. Lifts, end diaphragms, skew angle, and load type significantly decreased the distribution factors, while continuity and intermediate diaphragms had the least effect. If the bridge had been designed using the distribution factors calculated with the finite-element model rather than the code values, the required concrete release strength could have been reduced by 6.9 MPa (1,000 psi) or the live load could have been increased by 39%.     

Influence of Route Direction on Thermal Field of Embankments Constructed in High-Altitude Permafrost Area

This paper discusses the effect of route direction, embankment height, and pavement type on the thermal field of embankments built in permafrost regions. A finite-element model (FEM) is adopted to simulate diverse conditions of the embankment. The 30-year meteorological data including the solar radiation, air temperature, and wind velocity are used as the boundary conditions for the Qinghai-Tibet Highway. The results obtained from the FEM calculations are found to be in good agreement with the actual measurements on the thermal field. Further, the results show that route direction has great impact on the equilibrium of the thermal field within embankments in permafrost regions. The thermal imbalance is more obvious for embankments in the east–west direction and less in the north–south direction. In addition, the thermal asymmetry is closely related to seasonal variation and it is more pronounced in winter and less in summer.     

Evaluation of Floor Vibration in a Biotechnology Laboratory Caused by Human Walking

A floor supported on long-span beams, which was designed to accommodate bio research instruments, is evaluated for vibration induced by people walking. First, a brief review in vibration criteria is given. The variation of force time histories imposed by people’s feet on supporting objects is also discussed. Both beam and floor finite-element models are then used to simulate the local walking response of the floor mathematically. Footfall forces are applied to the finite-element models via triangular distribution function. A comparison of the time history analysis results with the vibration criteria shows that the floor performs well under people walking. Field measurements were also conducted after the completion of the construction. The measured results show a good correlation with the finite-element analysis results. During the analyses, it was also found that as long as the local floor model covers a structural bay, the boundary conditions of the floor model do not affect the response much. Using an equivalent constant footfall force function can produce similar results compared with those obtained using a more sophisticated force function.     

Friction Measurement on Cycleways Using a Portable Friction Tester

In seeking to promote cycling in wintertime, it is desirable to understand how important the winter maintenance service level is in people’s decision to cycle or not, and methods to compare different road conditions on cycleways are therefore needed. By measuring friction, an assessment of the service level can be achieved, but methods available often involve the use of large vehicles, which can lead to overloading damage on cycleways, and constitute a safety risk for cyclists and pedestrians. A portable friction tester (PFT), originally designed to measure friction on road markings, was thought to be an appropriate instrument for cycleways and was, therefore, tested on different winter road conditions, and on different cycleway pavement materials. In this study, it was found that the PFT is a valuable tool for measuring friction on cycleways. Different winter road conditions, as well as different pavement materials, can be distinguished from each other through PFT measurements. The PFT provides a good complement to visual inspections of cycleways in winter maintenance evaluation and can, for example, be used to determine if desired service levels have been achieved.     

Field Testing and Analysis of CRC Deck Girder Bridges

This paper presents findings of field tests and analysis of two conventionally reinforced concrete (CRC) deck girder bridges designed in the 1950s. The bridges are in-service and exhibit diagonal cracks. Stirrup strains in the bridge girders at high shear regions were used to estimate distribution factors for shear. Impact factors based on the field tests are reported. Comparison of field measured responses with AASHTO factors was performed. Three-dimensional elastic finite-element analysis was employed to model the tested bridges and determine distribution factors specifically for shear. Eight-node shell elements were used to model the decks, diaphragms, bent caps, and girders. Beam elements were used to model columns under the bent caps. The analytically predicted distribution factors were compared with the field test data. Finally, the bridge finite-element models were employed to compare load distribution factors for shear computed using procedures in the AASHTO LRFD and Standard Specifications.     

Effects of amniotic fluid embolism-like plasma on isolated perfused rabbit lungs

Information on road injury with analyses on the epidemiological features and determinants of fatality rate with prevention and control of road injury was presented in this paper. From 1951 to 1994, road injury and motor vehicle deaths had a continuous increase by 43 and 78 times respectively. Since 1987 about 250,000 cases, 5000 deaths and 15,000 trauma cases caused by road crashes year after year. The fatality rate increased by an average of 12.9% increase per year from 1984 to 1994 (from 2.43 to 5.56 per 100,000 pop). Zhejiang, Guangdong, Liaoning, Sichuan and Jiangsu occupied the first five places in 30 provinces, accounted for over 45% of total road injuries and one thirds of road fatalities. Both incidence and death rate were lowest in Beijing City and highest in Zhejiang Province. Three-quarters of the fatality on road injury were occurred on smooth and straight pavement in sunny days. Over 60% of the motor vehicle deaths were young males (age 20-50 yrs). Classified by occupation, majority of the victims were peasants (55%) and workers (19%). Two thirds of the road fatalities were pedestrians, bicycle riders and passengers. Human factors including driver's irresponsibility, non-licensing, bicycle rider and pedestrian carelessness, etc. were notified that accounted for over 90% of the causes for road injury. Primary causes from the drivers were rules and regulations violation, absent-mindedness, driving after drinking alcohol. The risk factors of road injuries were the increase of motor vehicles and traffic congestion. It is also necessary to improve the traffic safety knowledge among residents.     

Large Scale Discrete Element Modeling of Vehicle-Soil Interaction

This paper describes the current work on a large deformation soil model to demonstrate the feasibility of particle models to simulate full-scale vehicle-soil interaction problems in which the soil undergoes large excavation-like deformation. To achieve this objective, boundary conditions that accurately represent the vehicle geometry had to be incorporated into a 3D discrete element model. The approach taken was to use a finite-element grid to model the vehicle component interacting with the soil and develop routines to model the particle-grid interactions. The particle-grid interactions were more complicated than the particle-particle interactions required for the soil simulations and pose the greatest challenge to the use of computational parallelism. Two examples are presented in which vehicle components are modeled by finite elements that interact with 10 million discrete soil elements. Important theoretical issues are briefly noted concerning mechanics of granular media that are critical to acceptance of the nascent discrete element modeling technology.     

Prediction of Pavement Response during Freezing and Thawing Using Finite Element Approach

Although elastic multilayer techniques for pavement analysis have become increasingly popular through advances in software and personal computers, the difficulties of such methods in representing dynamic loading, pavement geometry and nonlinear material response are widely recognized as significant. Particularly in cold regions, where pavement materials are subject to seasonal freezing and thawing, nonlinear material behavior cannot be accurately modeled with these methods. However, many of these difficulties can be overcome by using the finite element method. In this study, an initial attempt to implement a commercially available finite element code in an analysis procedure for pavements in seasonal frost areas is presented. The results, compared with data from an extensively instrumented test road, show that surface deflections and the relative change in pavement stiffness, indicated by the subgrade strength index, are predicted very accurately. Although a time lag between maximum measured and predicted surface deflection is observed during thawing, the procedure is found to be promising and further research is warranted.