Saeed Mohammadzadeh

Sensor fusion of a railway bridge load test using neural networks

Field testing of bridge vibrations induced by passage of vehicle is an economic and practical form of bridge load testing. Data processing of this type of tests are usually carried out in a system identification framework using output measurements techniques which are categorized as parametric or nonparametric methods. These methods are based on the theory of probability. Learning theory which stems its origin from two separate disciplines of statistical learning theory and neural networks, presents an efficient and robust framework for data processing of such tests. In this article, the linear two layer feed forward neural network (NN) with back propagation learning rule has been adapted for strain and displacement sensors fusion of a railway bridge load test. The trained NN has been used for structural analysis and finite element (FE) model updating.

Stress-based fatigue reliability analysis ofthe rail fastening spring clipunder traffic loads

Nowadays, the rail fastening systems play an important role for preserving the connection between the rails and sleepers in various conditions. In this paper, stress based concept is used to develop a comprehensive approach for fatigue reliability analysisof fastening spring clip. Axle load, speed and material properties are assumed to be random variables. First, track and train models are analyzed dynamically in order to achieve displacement time history of fas-tening spring clip. Then this displacement time history is applied to the fastening spring clip in FE software to obtain variable ampli-tude of stresses. Crack nucleation life is calculated by rain-flow method and Palmgren-Miner linear damage rule. First Order Relia-bility Method (FORM) and Monte-Carlosimulation technique are employed for the reliability index estimations. The influences of various random variables on the probability of failure are investi-gated by sensitivity analysis. The results show that the equivalent stress range and material parameter have significant effect on fa-tigue crack nucleation.

Estimation of train derailment probability using rail profile alterations

Investigation of train derailment is a complicated job that occurs in special points with special characteristics. It depends on several variables so for successful predication, exact estimation of all effective parameters is required. Instead of this complicated job, usually a time history of variables and statistic distribution can be used. According to statistic distributions, exact determination of train derailment is practically impossible and therefore a probability function should be utilised. Angle of wheel flange, friction coefficient, axle load and train speed are effective parameters in investigation of train derailment probability. In this paper, by using statistical distributions, aforementioned parameters are investigated and derailment probability is calculated using reliability theory. To describe extra capabilities of model, derailment probability is calculated in three different curves of railway network considering real geometrical specifications of curves, amount of wear in rail profiles measured by EM120 track recording cars, axle load and operation speed.

Assessment of fracture reliability analysis of crack growth in spring clip type Vossloh SKL14

Spring clips type Vossloh SKL14 (fastening system of track) are vulnerable to fatigue damage in lifetime due to excitations caused by traffic loads. This article has tried to develop a method for reliability analysis of spring clips type SKL14, based on fracture mechanics approach. First of all, a linear dynamic analysis of track has been done for dynamic response calculations under various traffic loads. The displacement time histories are applied on finite element method of type Vossloh SKL14 to achieve cyclic stresses. The equivalent stress range is described by lognormal distribution. Then, fracture reliability analysis has been done for crack propagation assessment in spring clip based on Paris’s law. This fatigue crack growth is dominated by a Mode I mechanism. A linear limit state function based on fracture mechanics is derived in terms of random variables. First-order reliability method has been employed for reliability estimation. At the end, the influence of various random variables on overall probability of failure has been studied through sensitivity analysis.

Effects of maintenance operations on railway track's mechanical behaviour by field load testing

Deterioration of track causes variations in different mechanical parameters such as value and distribution of track vertical stiffness, which would change the way track mechanical components behave in service condition or maintenance operations. As a result, studying deterioration effects and that of maintenance operations such as tamping and dynamic stabilisation on the mechanical behaviour of both standard and deteriorated tracks could give a better picture of track condition and effectiveness of maintenance operations. In this paper, by carrying out static and dynamic tests and using 89 measurement sensors, the influence of mechanised maintenance operations on mechanical behaviours (strain, acceleration and displacement of rail and sleeper) of a high-deteriorated track and a low-deteriorated track is investigated. The tests were carried out in three different stages (before tamping, after tamping and after track dynamic stabilisation) under a passing train (a 6-axle locomotive and a 4-axle wagon) with 20-ton axle load. Observations indicate that track deterioration causes non-uniform track stiffness and load distribution along the track, such that rail heel strain time history under train loading changes from maximum tensional pattern under the wheels to maximum compressive pattern between two wheels of a bogie. Tamping and dynamic stabilisation cause a more uniform load distribution, which reduces strain and increases acceleration in rail and sleeper. Effects of these maintenance operations on sleepers are far more than that of rail. Deteriorated track is stiffer than low-deteriorated track; stiffness distribution is less uniform and its rails are subjected to less strain and acceleration.

Dynamic Forces at Square and Inclined Rail Joints: Field Experiments

AbstractInsulated rail joints (IRJs) are widely used in signaling and broken rail identification systems. Track deterioration adjacent to IRJ is frequent due to excessive dynamic forces generated at IRJs by the repetitive passage of the ongoing traffic. Hence, they exhibit low service life and are considered high-risk elements and maintained through high standards. With a view to increase operational speed and the annual operational throughput, many improved structural designs have been proposed, of which inclined IRJs are the focus of this paper. To compare noise, vibration, and adjacent sleepers’ vertical displacement of square and 30° and 45° cut joints, a series of field tests have been carried out in the Tehran-Karaj urban metro track. Results show that sleepers in the vicinity of 45° cut joint have less vertical displacements compared to that of 30° and square cut joints. Peak root-mean square (RMS) values of acceleration signatures of 30 and 45° cut joints are almost half the value for square joint...

A new field investigation on the lateral and longitudinal resistance of ballasted track

Track buckling is a complicated phenomenon that is caused by a wide range of parameters including the nature of track loading and the lateral and longitudinal resistance of a track. In this paper, the results of a field study on a test track in the Aprin railway station (in the southwest region of Tehran city) are presented to investigate the lateral and longitudinal resistance of the ballasted track. The lateral resistance of the track is measured by using both the single tie (sleeper) push test and the sleeper lateral pull test, and the results of the two methods are found to be compatible. The contributions of the ballast shoulder, crib, and the base part in the total lateral resistance are obtained for the loose and compacted ballast conditions, which showed good consistency with the presented data of literature. The longitudinal resistance is measured by using an innovative setup prepared on the test track. The measured longitudinal stiffness per sleeper is approximately twice of what was measured in the previous studies on track panels. The measured longitudinal stiffness during the unloading process is found to be 40% of the loading stiffness.

Field and numerical investigation of the effect of under-sleeper pads on the dynamic behavior of railway bridges

There is a growing need to minimise vibrations of railway structures, especially the railway bridges, due to the increasing speed of trains. Various methods are used to reduce the effects of vibration on bridges. One of the methods is using under-sleeper pads. In this study, a real railway bridge – located in the northern district of Iran – with two spans and a free span length of 7 m was selected for the investigation of the effect of under-sleeper pads on the reduction of vibrations imposed on railway bridges. Field experiments – including the installation of an accelerometer to measure the accelerations beneath bridge decks, on the rail web, and next to the sleeper, and also the installation of Linear variable differential transformers (LVDTs) to measure the displacements of midspan point of bridge decks – were conducted. The effect of under-sleeper pads on the reduction of vibration accelerations, displacements, and moments of bridge midspan was investigated by developing numerical models of the bridge and validating its results through experimental outputs. The modeling predicts that the reduction of acceleration imposed on the deck in the first and second spans was different; the reduction effects in the first span were higher, where there was 58% reduction after using under-sleeper pads beneath the sleepers. There was a 15% decrease in the displacement of the bridge deck when under-sleeper pads are used. Similar results were obtained for the midspan moment of the bridge which reduced by 16%.

Assessing ballast cleaning as a rehabilitation method for railway masonry arch bridges by dynamic load tests

Dynamic load testing has become a common practice for condition assessment of masonry arch bridges and lays the foundation for their rehabilitation procedures; however, additional dynamic testing after rehabilitation is rare. Carrying out dynamic load tests before and after rehabilitation programs produces valuable results with regard to the structural changes of the bridge. This paper tries to assess the effects of ballast cleaning on the performance of railway masonry arch bridges by conducting dynamic load tests before and after the rehabilitation procedure. To do so, a 70-year-old masonry arch bridge is instrumented with deflection meters and accelerometers. Dynamic load tests are carried out before and after ballast cleaning and results are compared. According to the test results, vertical deflections of different spots on the bridge remain the same, with a deviation of less than 5%. On the other hand, vibrations on the structure are reduced significantly. On average, vibration levels are reduced by 35% in different spots of the structure.

Enhancing the Structural Performance of Masonry Arch Bridges with Ballast Mats

AbstractA large portion of the railway bridge stock in many countries is comprised of masonry arch bridges. During recent years, more attention has been paid to the maintenance of such structures. ...