Increasing Axle Loads Research Articles

Highway bridge live loading assessment and load carrying capacity estimation using a health monitoring system

The Land Transport Authority of Singapore has a continuing program of highway bridge upgrading, to refurbish and strengthen bridges to allow for increasing vehicle traffic and increasing axle loads. One subject of this program has been a short span bridge taking a busy highway across a coastal inlet near a major port facility. Experiment-based structural assessments of the bridge were conducted before and after upgrading works including strengthening. Each assessment exercise comprised two separate components; a strain and acceleration monitoring exercise lasting approximately one month, and a full-scale dynamic test carried out in a single day. This paper reports the application of extreme value statistics to estimate bridge live loads using strain measurements.

Subsoil compaction caused by machinery traffic on a Swedish Eutric Cambisol at different soil water contents

Field traffic may reduce the amount of air-filled pores and cavities in the soil thus affecting a large range of physical soil properties and processes, such as infiltration, soil water flow and water retention. Furthermore, soil compaction may increase the mechanical strength of the soil and thereby impede root growth. The objective of this research was to test the hypotheses that: (1) the degree of soil displacement during field traffic depends largely on the soil water content, and (2) the depth to which the soil is displaced during field traffic can be predicted on the basis of the soil precompression stress and calculated soil stresses. In 1999, field measurements were carried out on a Swedish swelling/shrinking clay loam of stresses and vertical soil displacement during traffic with wheel loads of 2, 3, 5 and 7 Mg at soil water contents of between 11 and 35% (w/w). This was combined with determinations of soil precompression stress at the time of the traffic and predictions of the soil compaction with the soil compaction model SOCOMO. Vertical soil displacement increased with increased axle load. In May, the soil precompression stress was approximately 100 kPa at 0.3, 0.5 and 0.7 m depth. In August and September, the soil precompression stress at 0.3, 0.5 and 0.7 m depth was 550–1245 kPa. However, when traffic with a wheel load of 7 Mg was applied, the soil displacements at 0.5 m depth were several times larger in August and September than in May, and even more at 0.7 m depth. An implication of the results is that the precompression stress does not always provide a good indication of the risk for subsoil compaction. A practical consequence is that subsoil compaction in some soils may occur even when the soil is very dry. The SOCOMO model predicted the soil displacement relatively well when the soil precompression stress was low. However, for all other wheeling treatments, the model failed to predict that any soil compaction would occur, even at high axle loads. The measured soil stresses were generally higher than the stresses calculated with the SOCOMO model. Neither the application of a parabolic surface load distribution nor an increased concentration factor could account for this difference. This was probably because the stress distribution in a very dry and strongly structured soil is different from the stress distribution in more homogeneous soils.

Assessment of Highway Bridge Upgrading by Dynamic Testing and Finite-Element Model Updating

The Land Transport Authority of Singapore has a continuing program of highway bridge upgrading for refurbishing and strengthening bridges to allow for increasing vehicle traffic and increasing axle loads. One subject of this program has been a short-span bridge taking a busy main road across a coastal inlet near a major port facility. Experiment-based structural assessments of the bridge were conducted before and after upgrading works including strengthening. Each assessment exercise comprised three separate components: ~1! a strain and acceleration monitoring exercise lasting approximately one month; ~2! a full-scale dynamic test carried out in a single day without closing the bridge; and ~3! a finite-element model updating exercise to identify structural parameters and mechanisms. This paper presents the dynamic testing and the modal analysis used to identify the vibration properties and the quantification of the effectiveness of the upgrading through the subsequent model updating. Before and after upgrade, similar sets of vibration modes were identified, resem- bling those of an orthotropic plate with relatively weak transverse bending stiffness. Conversion of bearings from nominal simple supports to nominal full fixity was shown via model updating to be the principal cause of natural frequency increases of up to 50%. The utility of the combined experimental and analytical process in direct identification of structural properties has been proven, and the procedure can be applied to other structures and their capacity assessments.

Saving Ears or Fuel

This article discusses that freight carriers have their own sets of issues. Faced with the same economic pressures as long-haul trucks on the nation’s highways, freight trains are getting heavier and heavier, increasing axle loads and the forces that bear on the tracks. The challenges of minimizing wear and energy consumption are becoming more demanding for railroads. Managing friction between the wheel and the rail is an increasingly tough job, but a critical one for avoiding a host of performance problems and high costs. Friction modifiers are coatings that provide a controlled coefficient of friction at the contact point between the wheel tread and the top of the rail. The key point is control, which makes it possible to achieve a specific friction range. This is the main difference between friction modifiers and ordinary grease. CSX Corp. has begun tests of the two systems in cooperation with the Transportation Technology Center. The center has installed instrumentation in a section of track, and CSX has bought five TracGlide systems and five locomotive-mounted Lubriquip systems that will apply Kelsan’s friction modifier.

Acoustic emission to assess and monitor the integrity of bridges

Increased axle loads and traffic density necessitate strengthening and widening of traditional masonry arch bridges. The question remains as to how to evaluate the condition of a bridge and assess the effect of modern traffic on its serviceability? The focus of this paper has been the evaluation of the potential for the acoustic emission technique to provide cost effective in-situ long term monitoring of bridge condition. The work was performed on a bridge chosen to be representative of both masonry and reinforced concrete construction methods. The results demonstrate that acoustic emission technique can be applied to condition assessment of bridges. These results confirm that strong acoustic emission signals are obtained from reinforced concrete structures and demonstrate that acoustic emissions can be detected in masonry structures but at lower energy levels. The experimental programme has shown that AE is useful in detecting crack growth and determining the position of the crack tips at a much earlier stage in their development, before they are noticed during visual inspection

Enhancing freight railways for 30 tonne axle loads

An effective approach to decrease railway transportation costs is to invest in higher axle load and higher speed. Following a query from the Swedish iron-ore mining company LKAB, the railway infrastructure authorities of Banverket in Sweden and Jernbaneverket in Norway initiated a study of consequences and costs for an upgrading of axle loads from 25 to 30 tonnes (t) on Malmbanan and Ofotbanen. The influence of increased axle loads and improved bogie design on track structure degradation and costs for maintenance and reinvestments has been investigated. Full-scale field measurements of wheel-rail contact forces for the present iron-ore wagons with 25 t axle loads and for two types of prototype wagon with axle loads of 30 t have been performed. Computer simulations of dynamic wagon-track interaction and literature studies also provided information used in the estimation of track degradation rates. The total cost for upgrading the infrastructure to take 30 t axle loads was found to be lower than anticipated. As a consequence, five prototype wagons dimensioned for 30 t axle loads and radial self-steering bogies of the Scheffel HS type have been ordered and were delivered in early 1999 for tests on Malmbanan-Ofotbanen.

Increasing axle loads on railway bridges

AbstractUm die Wettbewerbsfähigkeit der Eisenbahnen im Bereich des Güterverkehrs zu erreichen, muß man Wege und Mittel finden, die Transportleistung zu verbessern. Am schnellsten gelingt dies, wenn man die zulässigen Achslasten im betroffenen Eisenbahnnetz erhöhen kann. In Schweden haben einige Firmen bereits neue Güterwagentypen mit höheren Achslasten entwickelt und fordern von Banverket die Genehmigung zum Einsatz dieser Wagen. Das schwedische Eisenbahnnetz entstand zum größten Teil in der zweiten Hälfte des 19. und in den ersten zwanzig Jahren des 20. Jahrhunderts. Nach relativ kurzer Zeit erfolgte damals eine dramatische Entwicklung bei der Herstellung von Eisenbahnwagen mit immer höheren Achslasten. Deshalb mußten schon in den ersten 20 Jahren unseres Jahrhunderts mehrere Brücken ersetzt werden, obwohl sie keineswegs alt oder abgenutzt waren. Daher stammen noch heute viele der älteren Eisenbahnbrücken in Schweden aus der Zeit von 1900 bis 1920. Für die Bemessung dieser Brücken wurden Achslasten zugrundegelegt, die hinsichtlich des damaligen Güterverkehrs mehr als ausreichten. Heutige Wagenladungen haben aber die Lasten, für die die Brücken bemessen wurden, bereits längst überschritten.

New techniques in the elastic analysis of arch bridges using image processing

AbstractThe importance of the masonry arch in Britain's infrastructure has never been more significant than at the present time with ever increasing axle loads under new EEC regulations The searches have been shown to be significantly affected by the overlying fill. The effect of this fill is being investigated by a number of methods employing a variety of experimental techniques. This paper presents one such new technique of examining the effects of the fill through monitoring zones of strain on an arch model subjected to load. The model arches were constructed in timber with a dry granular fill and approximately 90 tests were carried out to investigate the effect of load position, fill depth and pier stiffness. Image analysis of the tests permitted identification of the areas of strain within the fill and arch barrel and the location of the hinges at higher loads. Finite element (FE) analysis was used to model the arch in its elastic range and comparisons of the FE strain contour plots with the equivalent images illustrated the validity of using image processing for the determination of the strain characteristics. The practical applications of using such a technique are subsequently highlighted and commented on.

Predicting Pavement Distress in Oil Field Areas

A study on oil field traffic characteristics was performed and a procedure was developed for assessing current and future effects of oil field truck traffic on surface-treated (stage construction type) pavements. A computer program calculates several types of pavement distress and serviceability parameters to evaluate pavement performance under various axle load repetitions. Stepwise regression analysis of 132 surface-treated pavement sections led to the development of individual distress equations for rutting, raveling, flushing, alligator cracking, patching, longitudinal and transverse cracking, and failures (potholes). The versatility of the program provides a means of anticipating early pavement failures due to increased axle load repetitions. The program also provides the basic framework for computing the effects of other ''special-use'' truck traffic demands.

Ground vibrations from passing trains

As railway operating practice has evolved, so trains have become faster and also in the case of freight trains heavier, with increased axle loads. To carry this traffic, heavier track has been introduced and maintenance programmes intensified. This paper examines the residual problems of ground-borne vibration, the vehicle and track features which might be responsible for generation, how it is propagated, and how it might affect wayside buildings. Experimental work has suggested various significant features of railway design which might merit attention.