Civil Engineering Research Collection

Overuse of fertilizer and/or animal wastes has been cited as the reason for elevated nitrate concentrations in groundwater in agricultural areas. In coastal plain regions of the United States and in other areas where farming practices are conducted over aquifers in unconsolidated sediments, nitrate contamination may occur primarily as a result of climactic abnormalities even when the nutrients are used according to recommended practices. Water quality standards are often cited as a way to protect to protect groundwater quality. Research suggests that current best management practices are not capable of allowing producers in coastal plain regions to always comply with a nitrate standard for groundwater of 10mg/l of nitrate.

A field study utilizing simulated rainfall and bare plots 5.5m wide by 22m long was conducted to study the effectiveness of vegetated filter strips 4.6 and 9.2m long in removing nutrients and sediments from agricultural runoff. Losses of N and P from plots with filters were highly variable as compared to plots with no filters. Generally, nutrient removals appeared to be greater with the longer filters, but decreased as the number of runoff events increased. Mass losses of TSS, TN and TP in surface runoff were reduced by 66%, 0% and 27%, respectively, by 4.6m (15ft) long filters. TSS, TN and TP reductions by 9.2m (30ft) long filter strips of the lengths utilized in this study were effective in removing sediment from runoff but should not be relied upon as the primary means to reduce nutrient losses from agricultural areas.

Ground water quality is an environmental issue of national concern. Agricultural activities, because they involve large land areas, often are cited as a major contributor of ground water contamination. It appears that some degree of ground water contamination from agricultural land use is inevitable, especially where precipitation exceeds evapotranspiration. For this reason, and because agriculture differs significantly from point sources of pollution, farmers, policymakers, and scientists need alternative management strategies by which to protect ground water. Mathematical models coupled to geographic information systems to form expert systems can be important management tools for both policymakers and agricultural producers. An expert system can provide farmers, researchers, and environmental managers with information by which to better manage agricultural production systems to minimize ground water contamination. Significant research is necessary to perfect such a system, necessitating interim ground water management strategies that include not only a strong research program, but educational and public policy components as well.

The paper describes a field trial of the use of a simple statistical ‘extrapolation' technique for the determination of design load effects in existing bridges. Deflections were measured directly using lasers in the Foyle Bridge, and data were recorded for 155 daily 48-min samples. As only traffic load effects were of interest, wind-induced defections were removed by Fast Fourier transform analysis and temperature-induced deflections were removed through identification of traffic-free periods. A simple linear regression analysis using probability paper has been employed to determine the parameters which characterise the statistical distribution. The cumulative distribution function was then used to estimate the level of deflection with a 1000-year return period. Empirically derived formulas have been utilised to determine the variability in the 1000-year estimates and to calculate a design deflection which allows for this.

This paper highlights areas of inaccuracy in current modelling techniques for bridge decks with wide cantilevers. A 3-D grilllage model known as the upstand grillage is assessed by comparing its behaviour with that of a three-dimensional, finite-element model. Recommendation are made for the implementation of such a technique. The paper concludes with a comparison of results from analyses of a bridge deck using the standard and upstand grillage analogies and a three-dimensional finite-element method.

WAVE (Weigh-in-motion of Axles and Vehicles for Europe) is a research project, part-funded by the European Commission, with the objective of improving the accuracy and performance of Weigh-in-Motion (WIM) technology. It has a budget of the order of $ 2 million and will run from mid 1996 to mid 1998. It has close links and a substantial overlap of membership with COST323, a pan-European group with representatives from about 20 countries which coordinates nationally funded activities relating to WIM. The principal objectives of WAVE are: (i) to improve the accuracy of WIM systems, (ii) to develop a prototype pan-European WIM database, (iii) to develop calibration and testing procedures for WIM system performance and accuracy, particularly for cold climates and (iv) to develop a prototype fibre optic WIM sensor

The paper describes the use of algebraic linear programming for the minimum weight design of steel portal frames subject to the constraints of the Kinematic Theorem of plastic collapse. Minimum weight design is a classic linear programming problem which can be solved algebraically for classes of frames with arbitrary geometric dimensions and arbitrary load magnitudes. In a recent paper, the process of algebraic linear programming was reduced to the repeated application of a number of vector formulas and a computer program was developed for the derivation of the solution charts for specific classes of frames. In this paper the method is extended to the problem of frames subjected to multiple load cases. It is shown that simple problems whose solution can normally be displayed in the form of two-dimensional charts now require three-dimensional charts or a number of two-dimensional charts.

WIM has developed greatly in the last ten years and confidence in the accuracy of recorded data has increased significantly. Traffic data recently obtained from a number of representative European sites are used to re-calibrate the codified main load model of the European bridge loading code, Eurocode 1 Part 3. A wide range of real and virtual bridge forms were chosen for the study. Simulations were performed using free-flowing and jammed traffic. Load effects generated were determined and statistical extrapolations were performed, where appropriate, to determine characteristic values for the load effects. Some of the assumptions used in the derivation of the original loading model were reassessed.

For slab bridge decks with wide transverse edge cantilevers, the plane grillage analogy is shown to be an inaccurate method of linear elastic analysis due to variations in the vertical position of the neutral axis. The upstand grillage analogy is also shown to give inaccurate results, this time due to inappropriate modelling of in-plane distortions. An alternative method, known as upstand finite element analysis, is proposed which is sufficiently simple to be used on an everyday basis in the design office. The method is shown to give much better agreement than the others when compared with an elaborate three-dimensional solid finite element model. Single- and two-span bridge decks with solid and voided sections are considered for both longitudinal and transverse bending stresses.

This paper describes an experiment in which 2 independently developed bridge weigh-in-motion (WIM) systems are tested and compared, both for accuracy and durability. The systems, an Irish prototype still under development and a commercially available American system, were tested on a bridge in Slovenia. 11 statically pre-weighted trucks were each driven over the bridge several times at a range of typical highway speeds. Accuracies for axle and gross vehicle weights are presented within the framework of the draft European WIM specification, and the bias which can be introduced by the selection of a calibration truck is demonstrated. Performance factors relating to durability are also discussed with particular emphasis on axle detectors

This paper presents the formulation of a simple method for the prediction of the additional stresses induced in frame type integral bridges due to thermal expansion of the deck. These stresses are controlled to a large extent by the restraint provided to the deck by the backfill soil adjacent to the abutments. The first part of the paper develops a realistic means of assessing appropriate equivalent elastic stiffness values for the backfill using results from recent high quality laboratory soil testing. A boundary element type approach is then used to derive approximate general expressions, written in terms of the soil stiffness and the flexural rigidity of the abutment, for the lateral and rotational restraint provided by both the abutment and soil. These expressions are subsequently manipulated into a form that enables designers to make use of standard frame analysis computer programs for the prediction of thermal expansion effects. The proposed method is shown to compare well with predictions obtained using a finite element model of the soil and structure.

This paper describes a large scale test of six WIM systems and four additional sensors on an urban roadway in Zürich, Switzerland. Gross weights from some thousands of statically weighed vehicles were used to determine the levels of accuracy for each system, with reference to the new draft of the European specification on WIM (COST323). The accuracy of axle weights was not tested. The WIM sensors, which included one prototype were tested with the assistance of a recording and processing device supplied by the organiser. Most systems encountered some problems, failures and faults, under the carefully controlled conditions of the 30 month test. However, these were generally solved by the suppliers after some delay. Statistics are provided on overall levels of accuracy and on trends with season and time. In addition, a brief history of system malfunctions and failures is provided. Nevertheless the scope of the conclusions are limited by the traffic conditions and the test plan.

The results of an experimental road research project are presented which demonstrate the existence of spatial repeatability and show patterns of axle impact forces along a pavement. As part of the project, a section of highway near Paris, France, was instrumented with 18 weigh-in-motion sensors. Data was collected for a large number of vehicles over fourteen days between June 1994 and May 1995. For all the vehicles, the impact factors were calculated and typical graphs are presented which show the variation of impact factor with distance along the sensor array. Mean impact factors and coefficients of variation are also presented and differences between steel and air suspensions are highlighted. The influence of vehicle speed on maximum impact factor is also considered.

This is the second part of a two-part paper which addresses the issue of accuracy in weigh-in-motion (WIM) systems. The first part develops the statistical background necessary for any system of accuracy classification applied to a WIM system. This second part describes a draft European specification for the weigh-in-motion (WIM) of road vehicles, prepared by the COST 323 management committee. The philosophy behind the specification is outlined and the basic structure detailed. The specification gives an indication of what WIM accuracy might be achievable from sites with particular characteristics. There is a comprehensive review of methods of calibrating and testing WIM systems. Four types of calibration/test condition are described for tests using statically pre- or post-weighed vehicles. Accuracy classes are defined on the basis of the width of the confidence interval within which the measured results lie. Confidence interval widths arc specified for gross weights and weights of individual axles among other things. The percentage of test results which are required to fall within the confidence intervals is a function of the test conditions and the number of test runs. Examples using real WIM data illustrate the use of the specification.

Irish aggregates have a satisfactory history of service regarding alkali-aggregate reaction despite containing significant amounts of chert and use for a period in conjunction with cements of high alkali level. An investigation was conducted of the performance in the draft RILEM ‘ultra-accelerated mortar-bar test’ of 23 individual aggregates and 14 combinations found in Irish practice. An X-ray diffraction study was also carried out. Definitive expansion limits have yet to be finalised but a value of 0.15% after 14 days immersion has been suggested as the innocuous/deleterious threshold and 0.25% expansion is suggested as the lower limit for reactive aggregates. Despite their satisfactory history of use, almost half of the aggregates tested individually and one third of the combinations exceeded the innocuous/deleterious threshold value. However, the lower limit for reactive aggregates was reached by only four individual aggregates and by one of the combinations. The X-ray diffraction study revealed the presence of well-crystallised quartz, confirming the likelihood that the aggregates would not be reactive. The highest expansions were recorded in samples from argillaceous limestones and those containing small amounts of greywacke and chalcedonic chert. As expected, there was no correlation between chert content and degree of expansion. It is concluded that most Irish cherts are unreactive; that the draft mortar-bar test returns pessimistic results and is therefore a suitable screening test but could not be used universally for definitive assessment unless national expansion limits could be agreed in the place of use; and that X-ray diffractometry may be used in conjunction with the rapid screening test to assist early judgement on likely reactivity.

The objective of the WAVE project was to effect a significant step forward for those responsible  for road networks, through the following actions: Improve the capacity of conventional WIM systems to accurately estimate static loads from measurements of dynamic impact forces applied by axles, through use of arrays of sensors whose combined results can allow for the dynamic interaction between vehicle and pavement. Develop and improve the functioning and accuracy of bridge-based WIM systems through more sophisticated vehicle/bridge interaction modelling and data processing. Develop common data structures, formats and quality assurance procedures to facilitate the exchange and comparison of WIM data throughout Europe, to increase confidence in such  data and to provide reliable management information to decision makers. Perform tests of WIM systems to assess their durability and performance in various climatic conditions, particularly in cold regions where pavements deform and are weaker during the thaw and sensors are susceptible to studded tyres and de-icing salt. Develop standardised calibration methods  and  procedures  by improving  existing methods and extending their applicability to all European climates and types of WIM system. Develop and implement a new WIM technology,  based on an innovative fibre optic sensor  which has considerable potential in terms of quality and the extent of information provided and its insensitivity to harsh climatic conditions.This project constituted a strategic policy initiative to confirm the Europe's leadership in WIM. It led to the development of new technologies such as advanced multiple sensor and bridge WIM systems, a quality assurance procedure to be implemented in a pan-European database, data about the behaviour of WIM systems in harsh environments, an improvement in calibration procedures and  the development of a new European optic-fibre WIM technology. That will help road and transport decision makers.

This report gives results of some new studies performed to validate the European road traffic load model proposed by the Eurocode EC1. Weight in motion has developed greatly in the last ten years and confidence in the accuracy of recorded data has increased significantly. Traffic data recently obtained from a number of representative European sites are used to re-calibrate the codified main load model of the European bridge loading code, Eurocode 1 Part 3. A wide range of real and virtual bridge forms were chosen for the study. Simulations were performed using free-flowing and jammed traffic. Load effects generated were determined and statistical extrapolations were performed, where appropriate, to determine characteristic values for the load effects. Some of the assumptions used in the derivation of the original loading model were re-assessed.

This paper describes the simulation of free-flowing traffic across bridges to predict the characteristic values for bridge load effects such as bending moment and shear force. The results of these simulations are then used to demonstrate that, in predicting the characteristic extreme load effects to which a bridge may be subjected, it is not sufficient to solely model one- or two-truck presence events. It is shown that loading events involving three or more trucks may need be included in the model for short to medium spans. The critical loading events for a particular load effect are strongly dependent on the span and the shape of the influence line.

The Dynamic Amplification Factor for Bridges is of major concern in both their design and assessment. Research to date has focused on the single truck event. However, in many bridges the critical loading case is that of multiple truck presence on the deck. To accurately determine the dynamic amplification factor it is necessary to examine the effects of multiple trucks traversing a bridge. Experiments in Slovenia were carried out to examine the dynamic amplification factor for single and two truck events. Numerical models were constructed and validated from these experiments. These models were then used to compare the dynamic amplification factors produced from both single and multiple trucks crossing the bridge at various speeds. Important conclusions are drawn for bridge design and assessment purposes.