Showing papers on "Axle load published in 1998"

Method for Railroad Track Foundation Design. II: Applications

Abstract: A new design method has been developed to determine the granular layer thickness required to prevent and remedy railroad subgrade failures caused by repeated traffic loads. The design method emphasizes the effect of repeated loading on subgrade performance, and a procedure is incorporated to convert actual traffic conditions to a design dynamic wheel load and the equivalent number of repeated loads for the design period. The procedures for practical application of the design method are given in this paper. The design method was evaluated for several field cases and results were found to be consistent with field performance. These field cases include two test tracks and three track sites on two major railroads, where soft subgrade failures due to repeated axle loads were evaluated. Although the new design method is believed to provide the best approach currently available in taking into account the main load and track variables, future studies are recommended for further improvements and verifications.

Finite-Element Analyses of Flexible Pavements

Abstract: This study illustrates the usefulness of the finite-element method in the analysis of three-layer pavement systems subjected to different types of loading. The method is capable of simulating the observed responses of pavements subjected to axle loads with different tire pressures, axle loads with different configurations, and axle loads traveling at different speeds. A variety of material constitutive models such as linear elastic, nonlinear elastic, and viscoelastic are employed in the analyses to describe the behavior of the pavement materials. Finite-element modeling of pavements, if validated, can be extremely useful, because it can be used directly to estimate primary response parameters without resorting to potentially costly field experiments. If accurate correlations between the calculated and the measured primary response parameters can be obtained, then the analytical model can be used to calculate primary response load equivalency factors, utilizing deflection-based or strain-based equivalency factor methods.

Allocation of Pavement Damage Due to Trucks Using a Marginal Cost Method

Abstract: A procedure was developed for quantifying the pavement cost of proposed changes in regulations governing truck weights and dimensions, particularly the marginal cost method used for pavement cost allocation. The procedure was part of a comprehensive study undertaken by the Ontario Ministry of Transportation in response to government and industry initiatives to harmonize Ontario's truck regulations with those in surrounding jurisdictions. The marginal pavement cost of truck damage was defined as a unit cost of providing pavement structure for one additional passage of a unit truckload (expressed as equivalent single axle load). The results indicate that the highway type (or truck volumes associated with the highway type) has a major influence on marginal costs. For example, the annualized pavement life-cycle cost of the passage of one additional typical truck on 1 km of a highway in southern Ontario can range from about $0.004 for a freeway to $0.46 for a local road (Canadian dollars). The marginal cost method can be used to quantify pavement damage due to any axle load combination for both new and existing, in-service pavements. The knowledge of marginal costs would enable highway agencies to quantify the impact of specific regulatory changes of truck axle weights on pavement costs; for example, to quantify the pavement costs associated with increasing allowable truck weights of logging trucks on a specific segment of the highway network.

Axle Load Distribution Characterization for Mechanistic Pavement Design

Abstract: Proper consideration of traffic loading in pavement design requires knowledge of the full axle load distribution by the main axle types, including single, tandem, and tridem axles. Although the equivalent single axle load (ESAL) concept has been used since the 1960s for empirical pavement design, the new mechanistic-based pavement design procedures under development by various agencies most likely will require the use of the axle load distribution. Procedures and models for converting average daily traffic into ESALs and axle load distribution are presented, as are the relevant issues on the characterization of the full axle load distributions for single, tandem, and tridem axles for use in mechanistic-based pavement design. Weigh-in-motion data from the North Central Region of the Long-Term Pavement Performance study database were used to develop the models for predicting axle load distribution.

Evaluation of factors affecting wim system accuracy

Abstract: This paper describes all factors affecting the accuracy of WIM systems and of static wheel load scales. The common facts as well as the differences are worked out. The static wheel load scales are used as a basis, because they are widely used and accepted for law enforcement purpose. For the covering abstract see IRRD E102667.

Calibration of Mechanistic-Empirical Rutting Model for In-Service Pavements

Abstract: Rutting is a major failure mode for flexible pavements. Pavement engineers have been trying to control and arrest the development of rutting for years. Many models are available to relate pavement rutting to design features, traffic loading, and climatic conditions. These models range from purely empirical to mechanistic models. Mechanistic-empirical models (the Asphalt Institute and Shell) were used to predict the development of rutting for 61 Long-Term Pavement Performance (LTPP) test sections. The rutting damage, calculated using these models, did not appear to be a good predictor of the observed rutting depth. A new rutting model was developed and calibrated using the data from the 61 LTPP sections. The model accounts for the plastic deformation in all pavement layers and allows the use of actual axle load and type, rather than the equivalent single axle load, in characterizing traffic.

Dynamic interaction between instrumented vehicles and pavements

Abstract: In the scope of the OECD/DIVINE project (Element 5) experiments were carried out in France on several road sections with different profiles. Dynamic responses of two instrumented vehicles travelling at speed were investigated. Axle load variations were studied in the frequency/wavelength domain by spectral analysis, in order to identify the vehicle vertical dynamic motions. Amplitudes of such load variations were also related to the vehicle characteristics and the pavement profile. Comparisons are made between steel leaf spring and air 'road-friendly' suspension for one vehicle. Frequency and wavelength matching phenomena are pointed out, which in some cases cause dramatic increases in the dynamic loads. Some recommendations are suggested to reduce road damage, and to increase vehicle comfort and safety, which deal with heavy vehicle design, driving rules, and pavement maintenance. (a) For the covering entry of this conference, please see IRRD 895232.

Final research findings on traffic-load forecasting using weigh-in-motion data

Abstract: The overall objective of Project 7-987 was to develop a long-range pavement rehabilitation plan for a segment of US 59, a four-lane divided principal arterial highway in the Texas Department of Transportation's (TxDOT's) Lufkin District. To identify feasible pavement structures, test sections that would utilize most efficiently the existing pavements and materials were constructed in the southbound lanes near Corrigan, Texas. To quantify traffic loads on the test pavements, two weigh-in-motion (WIM) systems were installed: one two-lane system adjacent to the five rigid-pavement test sections located 8 km north of Corrigan, and the other adjacent to the five flexible-pavement test sections about 3 km south of Corrigan. These WIM stations were operated virtually continuously from 1993 through 1997 to record data about the date, time, speed, lane of travel, wheel loads, number of axles, and axle spacing of every southbound vehicle (about 7,500 per day) that crossed the sensors in each lane. In addition, special sensors were operated to collect sample data concerning the air and pavement temperature and the lateral position of the vehicle tires (single or dual) within each traffic lane. The result was an exceptionally comprehensive traffic data set. This final project traffic report complements and extends the time frame (to 5 years) of the traffic data analyses presented previously in Research Reports 987-5, -6, and -8. The traffic data analysis included exploration of patterns and trends in vehicle counts, lane use, and axle load frequency distributions by axle type, location on the vehicle, and vehicle class. The results indicated that on average during the 5 years, trucks accounted for about 28% of all southbound vehicles, and that five-axle tractor semitrailer trucks comprised about 62% of all trucks. Generally, 74% of the vehicles, and 82% of the trucks, traveled in the right-hand, southbound lane. The overall southbound vehicle count grew at an annual rate of approximately 2.5%, while five-axle tractor semitrailer trucks, the dominant truck class, increased in number about 6% each year. This suggests that traffic load forecasts should consider separately the respective growth rate for each vehicle class (by axle arrangement and axle-load frequency distribution) as the axles on each vehicle class cause different - often disproportionate - amounts of pavement damage.

Dynamic Behaviour of Ore Wagons in Curves at Malmbanan

Abstract: SUMMARY The transportation of ore can be made more cost efficient by use of bigger and heavier trains. An increase in axle load is thereby wanted. The fleet of ore wagons of today at Malmbanan/Ofotbanan in northern Sweden and Norway has to be updated. It is of interest to find out if it is possible to allow a higher axle load on the track with new wagons To be able to understand and predict the effects on track wear depending on what type of vehicle that is in use, the contact forces between wheels and rails have to be determined. A computer aided analysis has been made of the dynamic behaviour of three test vehicles equipped with different types of three-piece bogies running at Malmbanan. The vehicles are modelled and their interaction with the track is analysed using the multibody simulation package GENSYS The simulations show that, even if the axle load is increased from 25 tons to 30 tons and the velocity is increased from 50 km/h to 60 km/h, it is possible to reduce lateral track forces and wear in c...

Brake force distribution to axles of motor vehicle with anti-lock braking

Abstract: The method involves regulating the rear axle braking pressure with a common pressure regulating module (5) receiving a reservoir pressure and then setting the brake pressure fed to the front axle anti-lock valve purely mechanically/pneumatically for a fully laden vehicle. It involves measuring the braking pressure fed to the front axle anti-lock valve and determining the pressures at the front axle brake cylinders (10.1,10.2) from it and from the switching times of the anti-lock valve and then determining axle load distribution and exercising the anti-lock function at the rear axle only using the pressure regulation module (5). It has sensors to sense the position of the brake pedals and sends an electrical signal to an electronic control device. An Independent claim is also included for an arrangement for brake force distribution to the axles of a motor vehicle with anti-lock braking.

Prediction of Spatially Varying Track Settlement

Abstract: In this paper, the development and validation of a method to predict spatially varying track settlement is presented together with some practical applications. Using this method, proactive maintenance decisions can be made based on a detailed evaluation of present or future traffic conditions in terms of vehicle speed, axle load, suspension design and the condition of track structure and track geometry. These possible scenarios are illustrated by means of measured and predicted results.

Evaluation of extreme traffic load effects in cable stayed and suspension bridges using wim records

Abstract: The evaluation of load effects is fundamental for assessing bridge reliability. This paper presents an approach for extrapolating traffic effects to any return period. This method is performed through optimal fittings of Rice's formula from the tail of the level crossings histograms issued from the combination of WIM records and influence surfaces. Based on statistical tests, that allows the determination of an optimal number of classes to take into account in the fittings. The study of the load effects on the stay cables of the Burgundy bridge and of the total load supported by the main span of the Tancarville bridge highlights the use of the proposed method. For the covering abstract see IRRD E102667.

Orthotropic bridge weigh-in-motion for determining axle and gross vehicle weights

Abstract: This paper describes the ongoing project in which the suitability of an orthotropic bridge deck for bridge weigh-in-motion (B-WIM) purposes is tested. The main difference between the proposed system in this paper and other bridge WIM systems is that this system does not require any axle detectors on the road surface. Feasibility studies are conducted to find the most suitable algorithm for determining axle and gross vehicle weights. An identification algorithm based on the conjugate directions optimisation technique is developed and tested on experimental data, collected from an instrumented orthotropic bridge deck in eastern France. For the covering abstract see IRRD E102667.

Enhancing multiple-sensor wim systems

Abstract: A probabilistic estimation method for multiple-sensor WIM, based on the maximum likelihood estimator is presented. The theoretical analysis is based on two generic vehicle models and their frequency domain analogues: (a) a quarter car model, whose tyre force spectrum can be idealised by a single sinusoidal component in the frequency domain and (b) a walking beam model, corresponding to two sinusoidal components. The technique is able to determine the static axle load with considerably better accuracy than previous theoretical analyses. This work is part of the WAVE transport research project funded by the European Commission. For the covering abstract see IRRD E102667.

Concept for Mechanistic-Based Performance Model for Flexible Pavements

Abstract: A concept for a mechanistic-based performance model for flexible pavement was developed that considers the interaction between vehicles and pavement. A dynamic vehicle model was used to estimate the dynamic wheel force, and a three-dimensional finite element nonlinear dynamic pavement model was used to determine the dynamic pavement response. The effect of pavement roughness on vehicle bouncing and the effect of vehicle bouncing on the progression of pavement roughness were investigated under different roughness levels, suspension types, and layer thicknesses. The increase in roughness after each load repetition can be calculated using basic material properties from which the pavement service life can be estimated. The number of equivalent 80-kN single axle load repetitions to failure was estimated under different conditions without the need for empirical observations. It was found that the number of load repetitions to go from one level of present serviceability index (PSI) to the next largely decreases ...

Pavement Deterioration, Rate of Dynamic Force, and Ride Quality

Abstract: Pavement serviceability or ride quality indices have been widely applied to monitor pavement performance and deterioration for pavement rehabilitation, design, and other purposes. It is known that the ride quality or serviceability index of roads can be explained mainly by the vertical jerk experienced by raters sitting in a moving vehicle. However, it is not known to what extent that the indices have to do with some external traffic loading variables (e.g., the rate of dynamic forces or the dynamic forces exerted on a pavement surface by an axle load). Employing some actual road profiles and a half-axle load model, both the dynamic forces and the rate of dynamic forces exerted on a pavement surface are estimated using a spectral density method and a finite difference method, respectively. A very good correlation exists between these physical variables and the ride quality index or the serviceability index, indicating that the deterioration of pavement structures is closely related to the rate of dynamic forces.

A new era of overloading control in south africa

Abstract: This paper describes recent developments in South Africa both in terms of increased axle load limits and policies by the national and provincial road authorities to try and control heavy vehicle overloading and thereby protect an aging road network which is experiencing an accelerated rate of deterioration. As a result of a minimum level of enforcement in many areas, low levels of fines, limited success with prosecution in the courts and varying levels of corruption at weighbridges from country to country, many transport operators seem to have adopted a policy of deliberate overloading, some of which regularly overload their 22 metre combination vehicles by more than 40 tons. The concept and implementation of a new class of weighbridge or traffic control centre is described. A Stress-In-Motion (SIM) system, which has been developed in South Africa over the past five years, has also been installed as an experimental demonstration project at the Mantsole Traffic Control Centre. This system has been developed to measure three dimensional tyre/pavement contact stresses under moving tyre loads. Initial results show a significant difference between tyre inflation pressures and maximum and average vertical contact stresses for many tyre types under various loading conditions of heavy vehicles. (a) For the covering entry of this conference, please see IRRD 895232.

Pavement Distress Under Accelerated Trafficking

Abstract: A test pad was closely monitored for a 6-month period, with 640,000 axle load repetitions applied to the test pavement. The load was applied by the Texas Mobile Load Simulator, a full-scale accelerated loading device. Pavement performance data, such as rutting and cracking, were collected at intervals of 0; 2,500; 5,000; 10,000; 20,000; 40,000; 80,000; 160,000; 320,000; and 640,000 axle repetitions. Falling weight deflectometer (FWD) tests were performed at these same data collection intervals to characterize the structural capacity of the pavement system. Although there is a trend indicating that locations with higher FWD deflection result in higher rutting, a unique relation to predict rutting accurately from the surface deflection alone was not found in the study. The back-calculated asphalt concrete pavement moduli were reduced by 50 percent of the original value at the end of 320,000 repetitions. However, the test was not terminated until 640,000 repetitions, when moduli were reduced to 40 percent of...

Application of weigh-in-motion data to fatigue of road bridges

Abstract: Fatigue assessment of steel and composite bridges is one of the most demanding application of Weigh-In-Motion (WIM) in bridge engineering. Traffic data about axle and vehicle loads, spacing and volume are required to calculate fatigue damage and bridge lifetimes, to calibrate the conventional fatigue load models in the codes (and Eurocodes) and to check existing bridge reliability. An overview of the methods commonly used for bridge fatigue assessment is presented. Some information is given about the traffic data required and the fatigue load models of the Eurocode 1 Part 3. Finally some examples are given to show the sensitivity of the reliability of bridge details to traffic characteristics. For the covering abstract see IRRD E102667.

Accuracy assessment of a low speed weigh-in-motion system

Abstract: The lower the speed, the better the static weight estimation of an axle and a vehicle. This comes from the decrease of dynamics loads with speed. Low Speed Weigh In Motion (LS-WIM), on a designated area and at approximately 10 km/h, may be adapted for legal purposes such as overload enforcement. A LS-WIM system, manufactured by the French company Captels Inc., was tested on three different sites, in repeatability and reproducibility conditions, both in the laboratory and on operational sites. The tested device is portable, temporarily placed on the road with a ramp approach. The accuracy of the system is assessed with respect to the COST 323 European specification and the OIML International recommendations. For the covering abstract see IRRD E102667.

Spatial repeatability of dynamic loading on a pavement

Abstract: Spatial repeatability is the tendency for axle dynamic loads to present similar patterns along a given road profile. It may increase the intensity of pavement loading and pavement wear, as well as WIM accuracy. Trials were performed between 1994 and 1996 with a multiple sensor WIM system, in the frame of the OECD/DIVINE project (Element 5). The evidence of spatial repeatability was proved, and quantified by a spatial repeatability index (SRI). The influence of the road profile is shown, and the expected consequences on pavement wear are studied. Indications are also given about the potential effect on WIM accuracy. For the covering abstract see IRRD E102667.

Parametric sensitivity study of the AASHTO flexible pavement design equation

Abstract: The influence of design variables on the change in traffic capacity used for flexible highway pavement designed by the AASHTO procedure was studied. The change in the total equivalent single axle load (ESAL) that a pavement can carry due to a change in reliability level, overall standard deviation, structural number drop in serviceability index and the subgrade modulus of resilience, has been individually investigated. The AASHTO equation was simplified into different models that give the relationship between the change in each variable and the change in total ESAL to be carried by the highway pavement. The parametric sensitivity study showed that the structural number of the construction material and the subgrade modulus of resilience have The greatest effect on the load carrying capacity; whereas the change in serviceability index, reliability and overail standard deviation levels have relatively less effect.

Prediction of lateral wheel-rail contact forces for ore wagons with three-piece bogies

Abstract: The transportation of ore can be made more cost efficient by use of bigger and heavier trains. An increased load on the track gives higher demands on both vehicle and infrastructure performance in order to limit the maintenance cost. At Malmbanan/Ofotbanen in Sweden and Norway there are many tight curves along the track experiencing high wear. One criterion for allowing a higher axle load is therefore to reduce the lateral track forces compared to the level of today. To evaluate the effect of an increased axle load, instrumented wheelset measurements were performed on different test vehicles of three-piece type. The measurements show essential variations in lateral force levels depending not only on curve radius and coefficient of friction in the wheel-rail contact, but greatly on the actual individual curve. This effect is studied in this work. The curving performance of one of the vehicles when running through curves with different rail profiles have been simulated. Both simulations and experimental resultsshow large lateral forces for the typical situation on the studied track. The importance of matching wheel and rail profiles in order to get low contact forces and, as a consequence, less wear is shown.

Suspension system of two-front-axle vehicle

Abstract: PROBLEM TO BE SOLVED: To prevent a decrease in traction caused by the floating of rear wheels which occurs when only the front rear wheels of a two-front-axle vehicle are on a bump on the road or when traveling on an upwardly arched road surface by providing an equalizing function between the front front axle and front rear axle of the two-front-axle vehicle for an improved following property and to enhance the driving stability and riding comfort of the two-front-axle vehicle by distributing axle load evenly to the axles. SOLUTION: A torsion bar 2 is placed between a front front axle 6 and a front rear axle 8, and a first operating arm 3 connected to the front front axle 6 via a ball joint 20 and a second operating arm 4 connected to the front rear axle 8 via a ball joint are secured, respectively, to the front 2a and rear 2b ends of the torsion bar 2 to transmit the vertical movement of either one of the front front axle 6 or the front rear axle 8 to the other axle as movement in the opposite direction by use of the torsion spring force of the torsion bar 2 to give the two front axles 6, 8 an equalizing function.

Multiple sensors wim using reconstruction algorithms of the dynamic axles loads

Abstract: A method for the estimation of the static load of an axle from discrete measurements of its dynamic load is presented The proposed technique consists of the reconstruction of the dynamic variations of an axle load and uses considerations about vehicle-pavement interaction This research work belongs to the WP11 (MS-WIM) of the European project WAVE For the covering abstract see IRRD E102667

Equalizing suspension system

Abstract: PROBLEM TO BE SOLVED: To make the axle load distribution of front two axles during braking close to that during normal traveling and to enhance degrees of freedom for the size and shape of an equalizer link by decreasing the movement of axle load from a front front axle to a front rear axle that occurs during braking, in a front-two-axle vehicle whose front two axles are suspended by an equalizing suspension system. SOLUTION: A variable-damping-force-type shock absorber 56 or an oil cylinder is connected between a pin 40 and a frame 10 on an equalizer link 39 transmitting the relative movements of the leaf spring 34 of a front front axle 15 and the leaf spring 47 of a front rear axle 17 in opposite directions, and during braking either the damping force of the shock absorber 56 is increased or the cylinder is oil-locked.