Relative Longitudinal Displacement Research Articles

Investigation of longitudinal movements of girder ends considering various longitudinal non-linear resistances in railway suspension bridges

The functionality of expansion joints, bearings, and dampers in suspension bridges is directly impacted by the longitudinal movement of the girder ends. The complex longitudinal resistance of the girder significantly influences this movement in railway suspension bridges. This study develops an analytical model of a railway suspension bridge using measured displacement. The model encompasses various longitudinal nonlinear resistances, including girder-rail interaction, bearing friction, and viscous dampers, enabling a detailed analysis of longitudinal motion characteristics and deformation patterns of girder ends under train loads. This study investigates the effects of various longitudinal resistances on the movement of the girder and stress within the connecting components. A novel central buckle design is proposed to reduce the stress amplitude of the central buckles in railway suspension bridges. Results show that the innovative analysis model can accurately assess the longitudinal movement of girder ends in railway suspension bridges, aligning closely with the measured. The girder displays minimal longitudinal movement under train loads, owing to the longitudinal nonlinear resistances. However, there is a significant relative longitudinal displacement between the cable and girder in short hangers, leading to a considerable increase in bending stress and vast stress in the central buckle. Consequently, when studying the longitudinal movement in railway suspension bridges, it is critical to comprehensively analyze the longitudinal displacement of girder ends and the stress across various bridge components. The novel central buckle effectively mitigates excessive stress on the central buckle during train passage and simultaneously alleviates bending stresses of the short hangers. The findings of this study offer invaluable theoretical direction and practical engineering insights for the rational design of railway suspension bridges.

AutomAl 6000: Semi-automatic structural labelling of HAADF-STEM images of precipitates in Al–Mg–Si(–Cu) alloys

When the Al–Mg–Si(–Cu) alloy system is subjected to age hardening, different types of precipitates nucleate depending on the composition and thermomechanical treatment. The main hardening precipitates extend as needles, laths or rods along the <100> directions in the aluminium matrix. It has been found that the structures of all metastable precipitates may be generalized as stacks of <100> columns, where most of these columns are replaced by solute elements. In the precipitates, a column relates to neighbour columns by a set of simple structural principles, which allows identification of species and relative longitudinal displacement over the (100) cross-section.Aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is an important tool for studying such precipitates. With the goal of analysing atomic resolution HAADF-STEM images of precipitate cross-sections in the Al–Mg–Si(–Cu) system, we have developed the stand-alone software AutomAl 6000, which features a column characterization algorithm based on the symbiosis of a statistical model and the structural principles formulated in a digraph-like framework. The software can semi-autonomously determine the 3D column positions in the image, as well as column species. In turn, AutomAl 6000 can then display, analyse and/or export the structure data.This paper describes the methodology of AutomAl 6000 and applies it on three different HAADF-STEM images, which demonstrate the methodology. The software, as well as other resources, are available at http://automal.org. The source code is also directly available from https://github.com/Haawk666/AutomAl-6000.

Thermal evolution of CRTS Ⅱ slab track under various environmental temperatures: Experimental study

The environmental temperature plays an important role in thermal performance of materials and structure in CRTS Ⅱ ballastless slab track under operational condition. In this paper, two 1:4 geometric scaled models of five CRTS Ⅱ slab tracks on a simply-supported box girder under three environmental temperatures rising and dropping cases were conducted in a large-scale environmental simulation testing chamber, respectively. In order to study the effect of constraint conditions on the bond of cement asphalt mortar (CAM), the internal temperature distribution, stress and displacement of two scaled models with constraint and freedom boundary conditions are also compared. Results show that the internal temperatures, longitudinal stresses and displacements of the track structure increase nonlinearly within an increase of the environmental temperature. Accordingly, these same responses decrease linearly within a temperature decrease. Most importantly, when the environmental temperature variation is + 26.5℃, the testing axial force at the two ends of the prototype track structure reaches 2,849kN, and the relative longitudinal displacement between the track slab and base plate become larger with a decrease of the environmental temperature, especially for the lowest temperature of −20℃. Moreover, fixed constraint condition decelerates the temperature transfer of the track slab to CAM, since it leads to the larger absolute temperatures and stresses of the track structure compared to the free constraint.

Dynamic responses of bridge substructures subjected to high-speed trains

The substructures of high-speed rail (HSR) structures are typically rigid, as they are designed to meet stringent longitudinal displacement limits specified in most HSR design standards. For site conditions such as deep valleys and soft soils, tall columns or low foundation stiffness can lead to a flexible substructure system. Flexible substructures are preferred for bridges in seismic areas because their lower horizontal frequencies yield smaller seismic forces. This cost-effective design strategy is recognised in the California HSR design criteria manual, which specifies larger relative longitudinal displacement limits. In this work, the influences of substructure flexibility on relative displacements were investigated through dynamic analyses of 36 different numerical models representing a 20-span viaduct supported by substructures with first horizontal frequencies of 0.566–3.706 Hz. Four key parameters were investigated: column height, span length, bearing plan layout and ratio of depth to span length. Train models from BS EN 1991-2:2003 were used as dynamic moving loads. The results of this study show that the chances of dynamic responses larger than design limits do exist as the stiffness of substructures departs from being rigid, where resonance effects on substructures are the main contributor to response amplification.

Dynamic remodeling of the dynamin helix during membrane constriction

Dynamin is a dimeric GTPase that assembles into a helix around the neck of endocytic buds. Upon GTP hydrolysis, dynamin breaks these necks, a reaction called membrane fission. Fission requires dynamin to first constrict the membrane. It is unclear, however, how dynamin helix constriction works. Here we undertake a direct high-speed atomic force microscopy imaging analysis to visualize the constriction of single dynamin-coated membrane tubules. We show GTP-induced dynamic rearrangements of the dynamin helix turns: the average distances between turns reduce with GTP hydrolysis. These distances vary, however, over time because helical turns were observed to transiently pair and dissociate. At fission sites, these cycles of association and dissociation were correlated with relative lateral displacement of the turns and constriction. Our findings show relative longitudinal and lateral displacements of helical turns related to constriction. Our work highlights the potential of high-speed atomic force microscopy for the observation of mechanochemical proteins onto membranes during action at almost molecular resolution.

An equivalent linear model for shear pin fractures and its experimental verification

For bridges in seismically active areas, lower horizontal bearing stiffnesses are usually designed to reduce structural seismic responses and protect the piers and foundations against earthquake damage. But lower horizontal bearing stiffnesses are not preferred under normal service conditions. In the seismic designs of Chinese bridges, shear pins are extensively integrated into bearings to resist horizontal force and restrict the relative longitudinal displacement between the superstructure and the substructure under normal service conditions. Shear pins are designed to be sheared off in a certain earthquake to activate the seismic isolation mechanism. For lack of a proper constitutive model for shear pin fractures, effects of shear pin fractures have not been considered in current bridge seismic isolation designs yet. In order to establish a constitutive model of seismic isolation bearings considering shear pin fracture effects, shear fracture tests of shear pins were conducted and an equivalent linear model was established. Ultimate deformation and equivalent stiffness of the equivalent linear model are approximately proportional to the diameter of the shear pin, and load capacity is approximately proportional to the square of the diameter of the shear pin. A series of shaking table tests were conducted, and then test results were compared with numerical results calculated with the equivalent linear model. It was found the equivalent linear model was accurate enough and suggested to simulate the effects of shear pin fractures in bridge seismic designs.

지진하중을 고려한 장대레일교량의 궤도-교량 상호작용에 대한 안전성 평가

To observe the rail-slab interaction in continuous welded railway(CWR) bridge when earthquake occurs, additional axial rail stresses and relative longitudinal displacements between rail and bridge deck were calculated with input of various load combinations and 3 different types of seismic loads to an analytical model. As results of analysis, it can be found that standard response spectrum proposed by Korea Rail(KR) network authority for earthquake design showed less additional axial rail stresses than allowable levels, but greater relative longitudinal displacement between rail and bridge deck, which means that adjustment of relative longitudinal displacement within a standard level is much more difficult than axial train stress. Additionally, if a large-scaled earthquake as occurred at Kobe, Japan comes up, then both of additional axial rail stress and relative displacement in rail-bridge deck may exceed allowable levels, which indicates to make proper design guides against sudden earthquake occurrence.

Validation of color Doppler sonography for evaluating relative displacement between the flexor tendon and subsynovial connective tissue.

A common pathologic finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue. This finding suggests an etiology of excessive shear forces, with relative longitudinal displacement between the flexor tendon and adjacent subsynovial connective tissue. The purpose of this study was to validate color Doppler sonography for measurement of tendon displacement over time. Eight unmatched fresh frozen cadaver arms were used to evaluate color Doppler sonography for measurement of tendon displacement. The middle flexor digitorum superficialis tendon was moved through a physiologic excursion of 20 mm at 3 different tendon velocities (50, 100, and 150 mm/s). We found that color Doppler sonography provided accurate measurement of tendon displacement, with absolute errors of -0.05 mm (50 mm/s), -1.24 mm (100 mm/s), and -2.36 mm (150 mm/s) on average throughout the tendon excursion range. Evaluating relative displacement between the tendon and subsynovial connective tissue during finger flexion-extension movements also offered insight into the gliding mechanism of the subsynovial connective tissue. During flexion, we observed a curvilinear increase in relative displacement, with greater differential motion at the end range of displacement, likely due to the sequential stretch of the fibrils between successive layers of the subsynovial connective tissue. In extension, there was a linear return in relative displacement, suggesting a different unloading mechanism characterized by uniform relaxation of fibrils. We demonstrated the validity of color Doppler displacement for use in the evaluation of relative motion. Color Doppler sonography is useful in our understanding of the behavior of the subsynovial connective tissue during tendon excursion, which may elucidate the role of finger motion in the etiology of shear injury.

Loading-history-based track–bridge interaction analysis with experimental fastener resistance

Track–bridge interaction (TBI) analysis is usually required to determine the longitudinal stresses and displacements of a coupled system under various temperatures and trainloads and to guarantee the serviceability and safety of track structures. Its results can be used to determine the installation of rail expansion devices and even the structural designs of bridges. To improve calculation accuracy and assist with bridge design and construction investment decisions, this study proposed a nonlinear TBI analysis framework that accounted for the loading-history effects and changes in the longitudinal resistance of rail fasteners in various load cases. Laboratory experiments were conducted to determine the accurate nonlinear features of a kind of rail fastener commonly used in elevated urban rail transit traffic in China. The proposed method was applied in a case study to calculate the longitudinal stresses and displacements of a seven-span track–bridge system in comparison with the conventional linear superposition method. The results obtained using experimental longitudinal resistance displacement curves (RDCs) were also compared with those obtained using curves in the Eurocode. Both the calculation methods and the RDCs of rail fasteners were found to have considerable effects on longitudinal additional rail stresses and the relative longitudinal displacements between beam ends.

Magnetostatic waves in the gap between two ferromagnetic films that move relative to each other

The propagation of a magnetostatic gap wave in a gap between two ferromagnetic films with opposite magnetizations is considered under the conditions for relative longitudinal displacement. When the velocity of one film is reversed, the transformation of spectra is similar to the transformation in which each spectrum of magnetostatic wave with corresponding symmetry is split into two branches. It is demonstrated that significant modification of the magnetic field distribution in the gap structure occurs when the film moves along the energy propagation direction of the gap-wave mode.

A Simple Technique to Determine Interface Slip of Stud Connected SCC Girders

A simple technique is proposed to compute interface slip of stud connected steel-concrete composite (SCC) girders based on the results of a flexure test. The technique makes use of relative longitudinal displacement of the concrete slab and steel beam to calculate the interface slip. In the flexure test of a SCC girder, a cost-effective instrumentation arrangement consisting of mechanical dial gauges is used to measure the relative longitudinal displacement. Responses measured from experiments on SCC girders conducted by the authors are used for numerical implementation and validation of the technique. Alternatively, interface slip is also evaluated by applying an analytical model which is based on first principles of mechanics. The values of interface slip computed by using the proposed technique are found to have close correlation with those of the analytical model. The effect of edge restraint on slip due to friction between steel and concrete is also studied.

Тunneling of Acoustic Waves through the Gap between Two Ferromagnetic Crystals with the Relative Longitudinal Motion

The tunneling of a plane monochromatic acoustic wave through a gap between two ferromagnets under conditions of their relative longitudinal displacement has been considered. It has been shown that, the inclusion of the longitudinal displacement of one of the crystals, in all cases, leads to the violation of resonance conditions and, consequently, to a noticeable decrease in the coefficient of transmission of the acoustic wave through the gap between two ferromagnets; this effect is more pronounced, the higher is the velocity of motion of the crystal. It has been demonstrated that there is a possibility of the wave front reversal occurring with the amplification of the reflected magnetoacoustic wave.

Compensation of motion artifacts in intracoronary optical frequency domain imaging and optical coherence tomography

Intracoronary optical coherence tomography and optical frequency domain imaging (OFDI) have been utilized for two-dimensional and three-dimensional imaging of vascular microanatomy. Image quality and the spatial accuracy of multidimensional reconstructions, however, can be degraded due to artifacts resulting from relative motion between the intracoronary catheter and the vessel wall. To track the relative motion of a catheter with regard to the vessel, a motion tracking system was incorporated with a standard OFDI system by using wavelength division multiplexing techniques. Motion of the vessel was acquired by a frequency shift of the backscattered light caused by the Doppler effect. A single monochromatic beam was utilized for tracking the relative longitudinal displacements of a catheter-based fiber probe with regard to the vessel. Although two tracking beams are, in general, required to correct for longitudinal motion artifacts, the accurate reconstruction in a longitudinal view was achieved by the Doppler frequency information of a single beam. Our results demonstrate that the single beam based motion tracking scheme is a cost-effective, practical approach to compensating for longitudinal distortions due to cardiac dynamics, thus leading to accurate quantitative analysis of 3D intracoronary OFDI.

Displacement of conjugate points during a substorm in a global magnetohydrodynamic simulation

[1] We reproduce a magnetospheric reconfiguration under southward interplanetary magnetic field (IMF) conditions using numerical magnetohydrodynamic simulations. To investigate the relative displacements of the geomagnetic conjugate points, we trace both footprints of the geomagnetic field lines during the magnetospheric reconfiguration under positive and negative IMF By conditions. Several substormlike features, namely, the formation of a near-Earth neutral line, a fast earthward flow, and tailward releases of the plasmoid, occur about 1 h after a southward turning of the IMF. The surveyed field line traced from the near-Earth magnetotail was strongly distorted duskward in the north and south after the substorm onset for positive and negative IMF By, respectively. The maximum of the relative longitudinal displacement of both footprints is 4.5 and 5.5 h in magnetic local time for positive and negative IMF By, respectively. While observational studies have indicated that the IMF orientation is the main factor controlling the relative displacement of the conjugate points, the present simulation-based study with a constant IMF orientation shows for the first time that the combined effects of plasma pressure, magnetic field intensity, and the field-aligned current density distribution along the field line are likely to be major factors controlling the relative displacement of conjugate points.

Tunneling of magnetoacoustic waves through a gap in ferromagnetic crystals with a relative longitudinal displacement

The tunneling of a plane monochromatic acoustic wave through a gap between two ferromagnets under conditions of their relative longitudinal displacement has been considered. It has been shown that, when the gap thickness h is comparable to the wavelength, the complete transmission of the acoustic wave at the Damon-Eshbach frequency becomes possible. When the gap thickness is smaller than the wavelength, the complete transmission of the acoustic wave occurs but already at two resonant frequencies. The inclusion of the longitudinal displacement of one of the crystals, in all cases, leads to the violation of resonance conditions and, consequently, to a noticeable decrease in the coefficient of transmission of the acoustic wave through the gap between two ferromagnets; this effect is more pronounced, the higher is the velocity of motion of the crystal. It has been demonstrated that there is a possibility of the wave front reversal occurring with the amplification of the reflected magnetoacoustic wave.

Magnetostatic waves in the gap of ferromagnetic crystals with relative longitudinal displacement

The propagation of magnetostatic gap waves in the gap between two oppositely magnetized ferromagnets with a relative longitudinal displacement is considered. It is shown that the relative motion of the crystals has the form of the spectrum of magnetostatic waves. In particular, it is found that for certain values of the gap width, the velocity of relative motion of the crystals, and the magnetostatic wavelength, normal (anomalous) dispersion of the symmetric (antisymmetric) mode of the gap structure is transformed into the anomalous (normal) type of dispersion.

Magnetoelastic wave tunneling via a gap between ferroelectric crystals with relative longitudinal displacement

The tunneling of a plane monochromatic acoustic wave via a gap between two ferromagnetic crystals exhibiting relative longitudinal displacement has been studied. It is shown that, at a gap width comparable with the wavelength, the acoustic wave can exhibit complete transmission at the Damon-Eshbach mode frequency. If the gap width is much smaller than the wavelength, the complete transmission takes place at two resonance frequencies. Allowance for the longitudinal displacement of one crystal leads in all cases to violation of the resonance conditions, which results in a significant decrease in the transmission coefficient. The greater the velocity of crystal displacement, the stronger the decrease in the acoustic wave transmission though the gap between ferromagnetic crystals.

Interface guided modes in a photonic crystal heterostructure with a complete photonic band gap

In this paper, a new kind of photonic crystal heterostructure (PCH) with a complete photonic band gap, which is composed of two semi-infinite photonic crystals, consisting of a triangular array of circular air holes in homogeneous dielectric Si and a honeycomb array of circular dielectric Si rods in air, respectively, is proposed and demonstrated. The interface guided modes in the PCH are investigated by using the plane-wave expansion method. The influences of longitudinal sideslipping and transverse displacement of the lattices on interface guided modes are discussed. The simulation results show that the guided modes can exist in the heterostructure without any shift of the lattices and the number of guided modes strongly depends on the geometric parameters of the heterostructure. It is anticipated that the guided modes in this heterostructure can be achieved by adjusting the relative transverse or longitudinal displacement of the lattices.

Shear wave passage through a vacuum gap between piezoelectric crystals with relative longitudinal displacement

The influence of relative longitudinal displacements of two piezoelectric crystals separated by a vacuum gap on the reflection and transmission of shear waves through the gap between these crystals is considered. We predict the possibility of enhancing the reflected wave under conditions of wave front reversal for the wave transmitted through the gap.

Acoustic wave tunneling in a gap between hexagonal piezoelectric crystals with relative longitudinal displacement

The influence of relative longitudinal displacements of two hexagonal piezoelectric crystals on the refraction of acoustic waves in the gap between these crystals is considered.