Identification of Sleeper Support Conditions Using Mechanical Model Supported Data-Driven Approach

The ballasted track superstructure is characterized by a relative quick deterioration of track geometry due to ballast settlements and the accumulation of sleeper voids. The track zones with the sleeper voids differ from the geometrical irregularities with increased dynamic loading, high vibration, and unfavorable ballast-bed and sleeper contact conditions. This causes the accelerated growth of the inhomogeneous settlements, resulting in maintenance-expensive local instabilities that influence transportation reliability and availability. The recent identification and evaluation of the sleeper support conditions using track-side and on-board monitoring methods can help planning prevention activities to avoid or delay the development of local instabilities such as ballast breakdown, white spots, subgrade defects, etc. The paper presents theoretical and experimental studies that are directed at the development of the methods for sleeper support identification. The distinctive features of the dynamic behavior in the void zone compared to the equivalent geometrical irregularity are identified by numeric simulation using a three-beam dynamic model, taking into account superstructure and rolling stock dynamic interaction. The spectral features in time domain in scalograms and scattergrams are analyzed. Additionally, the theoretical research enabled to determine the similarities and differences of the dynamic interaction from the viewpoint of track-side and on-board measurements. The method of experimental investigation is presented by multipoint track-side measurements of rail-dynamic displacements using high-speed video records and digital imaging correlation (DIC) methods. The method is used to collect the statistical information from different-extent voided zones and the corresponding reference zones without voids. The applied machine learning methods enable the exact recent void identification using the wavelet scattering feature extraction from track-side measurements. A case study of the method application for an on-board measurement shows the moderate results of the recent void identification as well as the potential ways of its improvement.

Numerical Investigation on the Transverse Vibration of Prestressed Large-Span Beams with Unbonded Internal Straight Tendon

This paper deals with the effect of the prestress load on the free and forced dynamic behavior and vertical vibration of the prestressed beams. The analysis applies both the analytical frequency equation and the finite element method (FEM) using ABAQUS software to predict the fundamental natural frequency (FNF) of the simply supported unbonded prestressed beams. The energy method has been employed to derive the effective prestressing load to determine the eccentricity effect. In regard to the forced response of the prestressed beam, a moving point load with a constant value and various velocities and excitation frequencies is applied. Extensive parametric studies are carried out taking into account different factors including prestress load, eccentricity, concrete ratio, span-to-depth ratio, velocity, and frequency of the moving load. The comparison of the FNFs obtained by the formula with those obtained from FEM models indicates that the results are in a good agreement. This convergence demonstrates that the proposed formulation can predict the FNF of the eccentrically prestressed beams with high reliability. The time-histories curves for midspan displacement of the unbonded prestressed beams and the dynamic magnification factors are also evaluated. The results illustrate that the aforementioned factors have an indispensable contribution to the beam dynamic behavior.

About the Dynamic Behaviour of Composite Bars Reinforced with Cotton or Hemp Fibers

In this paper, the authors designed several green composites with natural reinforcements (hemp and cotton fibers) and the matrix is a synthetic resin (epoxy resin). On having produced the samples, the authors determined the dynamic mechanical characteristics. The dynamic parameters were determined from the bar free vibrations. The next experimental rig was used: the bars were clamped at one end and left free at the other end. At the free end, a Bruel&Kjaer accelerometer with 0.04 pC/ms-2 sensitivity was placed, in order to record the beam dynamic response. A force was applied at the free end to bend the beams, and after bending, the force was cancelled and the beams were left to vibrate freely. The accelerometer was connected to a Nexus signal conditioner, and the signal conditioner was connected to a SPIDER 8 data acquisition system made by Hottinger Baldwin Messtec. The acquisition system was connected to a notebook and the experimental parameters were obtained through the CATMAN EASY software. From the free vibrations recording, the next mechanical parameters were determined: the eigenfrequency of the first eigenmode, the damping factors per mass unit and per unit length, the loss factor and the dynamic Young modulus and stiffness. From the results obtained, it can be concluded that the materials with epoxy resin reinforced with hemp have better vibration damping properties as compared to the composites made from epoxy reinforced with cotton fibers.

Study the Effect of Substitution Filler on performance of Asphalt Mixture

The major distresses in asphalt pavements are rutting, fatigue, and adhesion loss (moisture susceptibility). In this research study, two substitution fillers (Cement and Lime) were used with two different aggregate quarries (based on minerals composition) to evaluate the relatively most beneficial combination of both fillers as well as an aggregate quarry to enhance the performance life of asphalt pavements, especially in under-developed countries. Four basic tests, (Asphalt Pavement Analyzer, Four Points Bending Beam, Dynamic Modulus, and Rolling Bottle Test) that used for the most desired properties of any asphalt pavement, were utilized to access the performance properties of modified asphalt mixture. Based on all laboratory test results this research study concludes that replacement of aggregate filler with hydrated lime and cement has a beneficial effect on asphalt mix performance and to save investment by using raw material. Substitution filler improves the high-temperature rut performance and intermediate temperature fatigue performance of asphaltic concrete mixture up to 25% to that of the conventional mixture. At the same time, substitution filler has more beneficial to improve 70% adhesion properties to that of the conventional mixture.

Integral Method for Flow Induced Transverse Vibrations Analysis of Flexible Pipes

This paper reviews some existing studies and numerical methods used for flow induced transverse vibrations analysis of flexible pipes. An integral method, based on the use of Green’s functions, already used for different straight beam dynamic analysis is adapted for the proposed subject. This approximate method leads to a matrix formulation and to an eigenvalue problem for free vibration analysis. The presented approach is able to estimate also the critical fluid velocities. Effects of boundary conditions and of elastic foundation characteristics, Coriolis terms and of other parameters on dynamic behavior of a pipe, can be included. Some numerical examples are also presented for comparisons with results obtained by FEM or with other data from literature. They show good agreement.