Laboratory Investigation into the Flexural Behavior of Embedded Concrete Sleepers in Two-Stage Concrete with Preplaced Ballast Aggregate

Morteza Esmaeili,Hamid Amiri 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.2

The conversion of ballasted railway tracks into slab tracks using the preplaced aggregate concrete (PAC) technology over the bridges and in the tunnels has been introduced by many researchers but the flexural behavior of this composite system has not yet been studied. Therefore, in the first stage, a series of mortar and concrete mixture designs were proposed and evaluated. Subsequently, a concrete beam mold with dimensions of 3 * 0.6 * 0.5 m, which represented the track conditions, was developed and the bending behavior of the constructed beams in both conditions of the presence and absence of the concert B70 sleeper were investigated. The maximum bending force in the middle of the concrete beam without a sleeper (SE) equaled 177.5 kN. In addition, the average values of bending tolerance by the sleeper including a PAC beam for three specimens in the four modes of the positive moment of midspan (SPM), negative moment of midspan (SNM), positive moment of rail seat (SPR), and negative moment of rail seat (SNR) were 55.25 kN m, 32.5 kN m, 91.84 kN m, and 38.21 kN m, respectively, which met the requirements of the AREMA regulations.

Laboratory Investigation on Preplaced Ballast Aggregate Concrete Deterioration over Freezing–Thawing Cycles

Morteza Esmaeili,Sajad Behnajad,Milad Hossein Esfahani 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.6

One of the major gaps in previous research on the mechanical behavior of ballasted railway tracks converted into slab tracks using the preplaced aggregate concrete technique is its durability against freezing and thawing cycles. The present study pioneers at investigating the Preplaced Ballast Aggregate Concrete (PBAC) deterioration during freezing–thawing cycles, in which several freeze–thaw tests were carried out to measure the weight loss of PBAC samples during various freezing–thawing cycles, as well as the reduction in both compressive/tensile strengths and the relative dynamic modulus of elasticity. Moreover, the image acquisition of the PBAC samples was performed using a digital microscope and subsequently, an image processing technique was utilized to find a relation between the surface defect area at each imposed cycle and the number of cycles as a lifetime representative. As a result, an equation was developed to predict the defect frequency versus imposed cycles and the defect area generated to find the serviceability lifetime of PBAC in aggressive weather conditions. It was concluded that such PBAC can tolerate 6.16 years in the regions with full freezing–thawing weather conditions.

Dynamic instability response in nanocomposite pipes conveying pulsating ferrofluid flow considering structural damping effects

Esmaeili, Hemat Ali,Khaki, Mehran,Abbasi, Morteza Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.3

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton's principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin's method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.

Dynamic stability of nanocomposite Mindlin pipes conveying pulsating fluid flow subjected to magnetic field

Esmaeili, Hemat Ali,Khaki, Mehran,Abbasi, Morteza Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.1

In this work, the dynamic stability of carbon nanotubes (CNTs) reinforced composite pipes conveying pulsating fluid flow is investigated. The pipe is surrounded by viscoelastic medium containing spring, shear and damper coefficients. Due to the existence of CNTs, the pipe is subjected to a 2D magnetic field. The radial induced force by pulsating fluid is obtained by the Navier-Stokes equation. The equivalent characteristics of the nanocomposite structure are calculated using Mori-Tanaka model. Based on first order shear deformation theory (FSDT) or Mindlin theory, energy method and Hamilton's principle, the motion equations are derived. Using harmonic differential quadrature method (HDQM) in conjunction with the Bolotin's method, the dynamic instability region (DIR) of the system is calculated. The effects of different parameters such as volume fraction of CNTs, magnetic field, boundary conditions, fluid velocity and geometrical parameters of pipe are shown on the DIR of the structure. Results show that with increasing volume fraction of CNTs, the DIR shifts to the higher frequency. In addition, the DIR of the structure will be happened at lower excitation frequencies with increasing the fluid velocity.

Dynamic stability of nanocomposite Mindlin pipes conveying pulsating fluid flow subjected to magnetic field

Hemat Ali Esmaeili,Mehran Khaki,Morteza Abbasi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.1

In this work, the dynamic stability of carbon nanotubes (CNTs) reinforced composite pipes conveying pulsating fluid flow is investigated. The pipe is surrounded by viscoelastic medium containing spring, shear and damper coefficients. Due to the existence of CNTs, the pipe is subjected to a 2D magnetic field. The radial induced force by pulsating fluid is obtained by the Navier-Stokes equation. The equivalent characteristics of the nanocomposite structure are calculated using Mori-Tanaka model. Based on first order shear deformation theory (FSDT) or Mindlin theory, energy method and Hamilton’s principle, the motion equations are derived. Using harmonic differential quadrature method (HDQM) in conjunction with the Bolotin’s method, the dynamic instability region (DIR) of the system is calculated. The effects of different parameters such as volume fraction of CNTs, magnetic field, boundary conditions, fluid velocity and geometrical parameters of pipe are shown on the DIR of the structure. Results show that with increasing volume fraction of CNTs, the DIR shifts to the higher frequency. In addition, the DIR of the structure will be happened at lower excitation frequencies with increasing the fluid velocity.

Dynamic instability response in nanocomposite pipes conveying pulsating ferrofluid flow considering structural damping effects

Hemat Ali Esmaeili,Mehran Khaki,Morteza Abbasi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.3

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton’s principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin’s method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.

Development of optimum modeling approach in prediction of wheelflats effects on railway forces

Javad Sadeghi,Amin Khajehdezfuly,Morteza Esmaeili,Davood Poorveis 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.5

While the wheel flat is an asymmetrical phenomenon in the railway, majority of researches have used two-dimensional models in the investigation of the effect of wheel flat on the wheel rail forces. This is due to the considerably low computational costs of two dimensional (2D) models although their reliability is questionable. This leaves us with the question of “what is the optimum modeling technique?”. It is addressed in this research. For this purpose, two and three dimensional numerical models of railway vehicle/track interaction were developed. The three dimensional (3D) model was validated by comparisons of its results with those obtained from a comprehensive field tests carried out in this research and then, the results obtained from the 2D and 3D models were compared. The results obtained indicate that there are considerable differences between wheel/rail forces obtained from the 2D and 3D models in the conditions of medium to large wheel-flats. On the other hand, it was shown that the results of the 2D models are reliable for particular ranges of vehicle speed, railway track stiffness and wheel-fats lengths and depths. The results were used to draw a diagram, which presents the optimum modeling technique, compromising between the costs and accuracy of the obtained results.

Experimental investigation on the effectiveness of under-foundation isolator against train-induced vibrations considering foundation type

Ehsan Haghighi,Javad Sadeghi,Morteza Esmaeili 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.89 No.2

In this paper, the performance of under-foundation isolators against generally annoying train-induced vibrations was examined experimentally. The effect of foundation type on the efficacy of such isolators was investigated for the first time. To this end, laboratory models including a soil container, soil, building with three types of foundation (i.e., single, strip, and mat), and isolator layer were employed. Through various dynamic tests, the effects of foundation type, isolation frequency, and the dominant frequency of train load on the isolator’s performance were studied. The results demonstrated that the vibration level in the unisolated building with the strip and mat foundation was, respectively, 29 and 38% lower than in the building with the single foundation. However, the efficacy of the isolator in the building with the single foundation was, respectively, 21 and 40% higher than in the building with the strip and mat foundation. Furthermore, a lower isolation frequency and a higher excitation frequency resulted in greater isolator efficacy. The best vibration suppression occurred when the excitation frequency was close to the floor’s natural frequency.

Performance of under foundation shock mat in reduction of railway-induced vibrations

Javad Sadeghi,Ehsan Haghighi,Morteza Esmaeili 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.4

Under foundation shock mats have been used in the current practice in order to reduce/damp vibrations received by buildings through the surrounding environment. Although some investigations have been made on under foundation shock mats performance, their effectiveness in the reduction of railway induced-vibrations has not been fully studied, particularly with the consideration of underneath soil media. In this regard, this research is aimed at investigating performance of shock mat used beneath building foundation for reduction of railway induced-vibrations, taking into account soil-structure interaction. For this purpose, a 2D finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a shock mat, and the building. The model results were validated using an analytical solution reported in the literature. The performance of shock mats was examined by an extensive parametric analysis on the soil type, bedding modulus of shock mat and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, a better performance of shock-mats is observed. A simplified model/method was developed for prediction of shock mat effectiveness in reduction of railway-induced vibrations, making use of the results obtained.

Vehicle/track dynamic interaction considering developed railway substructure models

Seyed-Ali Mosayebi,Jabbar-Ali Zakeri,Morteza Esmaeili 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.6

This study is devoted to developing many new substructure models for ballasted railway track by using the pyramid model philosophy. As the effect of railway embankment has been less considered in the previous studies in the field of vehicle/track interaction, so the present study develops the pyramid models in the presence of railway embankment and implements them in vehicle/track interaction dynamic analyses. Considering a moving car body as multi bodies with 10 degrees of freedom and the ballasted track including rail, sleeper, ballast, subgrade and embankment, two categories of numerical analyses are performed by considering the new substructure systems including type A (initiation of stress overlap areas in adjacent sleepers from the ballast layer) or type B (initiation of stress overlap areas in adjacent sleepers from the subgrade layer). A comprehensive sensitivity analyses are performed on effective parameters such as ballast height, sleepers spacing and sleeper width. The results indicate that the stiffness of subgrade, embankment and foundation increased by increasing the ballast height. Also, by increasing the ballast height, rail and ballast vertical displacement decreased.