Longitudinal Constraint Research Articles

Multiobjective Optimal Control of Longitudinal Seismic Response of a Multitower Cable-Stayed Bridge

The dynamic behavior of a multitower cable-stayed bridge with the application of partially longitudinal constraint system using viscous fluid dampers under real earthquake ground motions is presented. The study is based on the dynamic finite element model of the Jiashao Bridge, a six-tower cable-stayed bridge in China. The prime aim of the study is to investigate the effectiveness of viscous fluid dampers on the longitudinal seismic responses of the bridge and put forth a multiobjective optimization design method to determine the optimized parameters of the viscous fluid dampers. The results of the investigations show that the control objective of the multitower cable-stayed bridge with the partially longitudinal constraint system is to yield maximum reductions in the base forces of bridge towers longitudinally restricted with the bridge deck, with slight increases in the base forces of bridge towers longitudinally unrestricted with the bridge deck. To this end, a multiobjective optimization design method that uses a nondominating sort genetic algorithm II (NSGA-II) is used to optimize parameters of the viscous fluid dampers. The effectiveness of the proposed optimization design method is demonstrated for the multitower cable-stayed bridge with the partially longitudinal constraint system, which reveals that a design engineer can choose a set of proper parameters of the viscous fluid dampers from Pareto optimal fronts that can satisfy the desired performance requirements.

Longitudinal force in continuously welded rail on long-span tied arch continuous bridge carrying multiple tracks

Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube (CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a (77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail (CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load. Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.

Passive control system for seismic protection of a multi-tower cable-stayed bridge

The performance of passive control system for the seismic protection of a multi-tower cable-stayed bridge with the application of partially longitudinal constraint system is investigated. The seismic responses of the Jiashao Bridge, a six-tower cable-stayed bridge using the partially longitudinal constraint system are studied under real earthquake ground motions. The effects of the passive control devices including the viscous fluid dampers and elastic cables on the seismic responses of the bridge are examined by taking different values of parameters of the devices. Further, the optimization design principle of passive control system using viscous fluid dampers is presented to determine the optimized parameters of the viscous fluid dampers. The results of the investigations show that the control objective of the multi-tower cable-stayed bridge with the partially longitudinal constraint system is to reduce the base shears and moments of bridge towers longitudinally restricted with the bridge deck. The viscous fluid dampers are found to be more effective than elastic cables in controlling the seismic responses. The optimized parameters for the viscous fluid dampers are determined following the principle that the peak displacement at the end of bridge deck reaches to the maximum value, which can yield maximum reductions in the base shears and moments of bridge towers longitudinally restricted with the bridge deck, with slight increases in the base shears and moments of bridge towers longitudinally unrestricted with the bridge deck.

Seismic performance and its favorable structural system of three-tower suspension bridge

Due to the lack of effective longitudinal constraint for center tower, structural stiffness of three-tower suspension bridge becomes less than that of two-tower suspension bridge, and therefore it becomes more susceptible to the seismic action. By taking a three-tower suspension bridge-the Taizhou Highway Bridge over the Yangtze River with two main spans of 1080 m as example, structural dynamic characteristics and seismic performance of the bridge is investigated, and the effects of cable\'s sag to span ratio, structural stiffness of the center tower, and longitudinal constraint of the girder on seismic response of the bridge are also investigated, and the favorable structural system is discussed with respect to seismic performance. The results show that structural response under lateral seismic action is more remarkable, especially for the side towers, and therefore more attentions should be paid to the lateral seismic performance and also the side towers. Large cable\'s sag, flexible center tower and the longitudinal elastic cable between the center tower and the girder are favorable to improve structural seismic performance of long-span three-tower suspension bridges.

Longitudinal Vibration Control of Long-Span Railway Cable-Stayed Bridge

As the floating type cable-stayed bridge has no longitudinal constraint between the main girder and the pylon, it may cause the main girder a large longitudinal displacement and the root of tower a large longitudinal bending moment, and affect the normal use and safety of the bridge under the earthquake or the train braking. It is an important part of the design to select an appropriate vibration control scheme. Taking a long-span railway bridge for example, this paper build the finite element model and analyses the damping effect in the view of train braking, moreover, the present study also examines the dynamic behavior with focus on two parameters of damping coefficient C and damping exponent αof the viscous dampers through dynamic time-history analysis. The results show that setting viscous dampers with the reasonable parameters can reduce the vibration and the response of the bridge by train braking and have a good energy dissipation effect.

Model of the Jovian magnetic field topology constrained by the Io auroral emissions

[1] The determination of the internal magnetic field of Jupiter has been the object of many studies and publications. These models have been computed from the Pioneer, Voyager, and Ulysses measurements. Some models also use the position of the Io footprints as a constraint: the magnetic field lines mapping to the footprints must have their origins along Io's orbit. The use of this latter constraint to determine the internal magnetic field models greatly improved the modeling of the auroral emissions, in particular the radio ones, which strongly depends on the magnetic field geometry. This constraint is, however, not sufficient for allowing a completely accurate modeling. The fact that the footprint field line should map to a longitude close to Io's was not used, so that the azimuthal component of the magnetic field could not be precisely constrained. Moreover, a recent study showed the presence of a magnetic anomaly in the northern hemisphere, which has never been included in any spherical harmonic decomposition of the internal magnetic field. We compute a decomposition of the Jovian internal magnetic field into spherical harmonics, which allows for a more accurate mapping of the magnetic field lines crossing Io, Europa, and Ganymede orbits to the satellite footprints observed in UV. This model, named VIPAL, is mostly constrained by the Io footprint positions, including the longitudinal constraint, and normalized by the Voyager and Pioneer magnetic field measurements. We show that the surface magnetic fields predicted by our model are more consistent with the observed frequencies of the Jovian radio emissions than those predicted by previous models.

SU‐GG‐T‐523: A Creative Measure to Ensure the Accuracy of Removable SRS Mask

Purposes: To analyze geometrical uncertainties of Brainlab SRS head mask system during clinical practice, and evaluate the effectiveness in limiting the uncertainty by introducing a special longitudinal restraint. Material and Method: From June, 2009 to February, 2010, total 24 intracranial lesions were treated with Brainlab SRS mask system on Varian NTX at our center. All patients were immobilized with Brainlab head mask system, which was made about 15 minutes prior to simulation. The removable frame consists of a back and front thermoplastic mashes; reinforcing pieces cross the forehead and upper lip attached by a nose bridge and bite pieces. In the test group, a longitudinal restraint was extended cross the top of head. The mask is attached to a U shaped base ring for rigid geometric registration of simulation CT. During the treatment the setup of Brainlab's localizer was compared with CBCT. Results: The mean 3D displacement of 16 cases with Brainlab SRS mask was 4.1 ±1.5mm. Their vertical, longitudinal, and lateral shifts were 1.6 ±1.0mm, 3.2 ±1.9mm (p < 0.01), and 1.1 ±0.9mm respectively. Averaging all 8 cases in the test group using the longitudinal constraint, the shift was reduced to 0.3 ±0.5 mm (p<0.01). The only 2 cases were shifted, only by 1mm, and identified after CBCT to be caused by operator's oversight. Conclusion: During treatment setups for less cooperative patients, the accuracy of commercial Brainlab SRS head mask system can be easily compromised due to altered the pitch angle or longitudinal position of the head inside the mask. Due to this reason, we found greater variations in our practice for SRS setups using Brainlab's removable frame. The introduction of longitudinal restraint has demonstrated its effectiveness in ensuring the accuracy of this system.

Excess energy and deformation along free edges of graphene nanoribbons

Change of the bonding environment at the free edges of graphene monolayer leads to excess edge energy and edge force, depending on the edge morphology (zigzag or armchair). By using a reactive empirical bond-order potential and atomistic simulations, we show that the excess edge energy in free-standing graphene nanoribbons can be partially relaxed by both in-plane and out-of-plane deformation. The excess edge energy and edge force are calculated for graphene nanoribbons with parallel zigzag or armchair edges. Depending on the longitudinal constraint, the compressive edge force leads to either in-plane elongation of the ribbon or out-of-plane buckling deformation. In the former case, the longitudinal strain is inversely proportional to the ribbon width. In the latter case, energy minimization predicts an intrinsic wavelength for edge buckling to be 6.2 nm along the zigzag edge and 8.0 nm along the armchair edge. For graphene nanoribbons of width less than the intrinsic wavelength, interaction between the two free edges becomes significant, leading to anti-phase correlation of the buckling waves.

Analysis of the internal structure of a carbonate damage zone: Implications for the mechanisms of fault breccia formation and fluid flow

A segment of the Salzach-Ennstal fault zone (Talhof fault, Eastern Alps) shows evidence for joint nucleation by layer-parallel shear, causing the formation of joint-bounded slices oriented at high angles (65–85°) with respect to the shear zone boundary (SZB). Subsequent slice rotation resulted in joint reactivation as antithetic shears, slice kinking, and breaking-up of the individual slices into smaller fragments. The latter process, due to the longitudinal constraint of slices with impeded shear zone widening, marked the transition to cataclasite formation and fault core evolution during shear localization. Cataclasites were subsequently cemented and underwent continuous shear deformation by re-fracturing. Cement precipitation from fluids therefore played a fundamental role in the evolution of the fault zone, with a cyclic change between an open and a closed permeability system during fault evolution. Stable isotope compositions (δ 13C, δ 18O) of fault rock cements indicate a continuous equilibration between protolith-derived fragments and cements precipitated from those fluids. This points to limited fluid amounts, only temporally replenished by meteoric water, and a hydraulic gradient that directed fluid flow from the damage zone towards the fault core.

Limit of axial force ratio and requirement for stirrups of RC columns with special shape

Thousands of columns with special shape are analyzed by nonlinear numerical methods. The ductility is calculated to investigate the limit of the axial force ratio and circumstantial requirement for stirrups of an reinforced concrete (RC) column with special shape, in the point of view of the characteristic value for providing stirrup. The limit of the axial force ratio of columns with special shape in relation to the characteristic value of the stirrup is obtained. Then, the effect of stirrup arrangement on the ductility of the RC column is discussed in case of buckling of the longitudinal reinforcement and constraint concrete columns. The complete requirement for stirrups of RC column with special shape is given.

3D phase diversity: a myopic deconvolution method for short-exposure images: application to retinal imaging

3D deconvolution is an established technique in microscopy that may be useful for low-cost high-resolution imaging of the retina. We report on a myopic 3D deconvolution method developed in a Bayesian framework. This method uses a 3D imaging model, a noise model that accounts for both photon and detector noises, a regularization term that is appropriate for objects that are a mix of sharp edges and smooth areas, a positivity constraint, and a smart parameterization of the point-spread function (PSF) by the pupil phase. It estimates the object and the PSF jointly. The PSF parameterization through the pupil phase constrains the inversion by dramatically reducing the number of unknowns. The joint deconvolution is further constrained by an additional longitudinal support constraint derived from a 3D interpretation of the phase-diversity technique. This method is validated by simulated retinal images.

A HYBRID FINITE SEGMENT/FINITE ELEMENT MODELLING AND EXPERIMENT ON A FLEXIBLE DEPLOYMENT SYSTEM

This paper focuses on the dynamic responses of a flexible deployment system that has a central rigid body and four articulated flexible beams and undergoes locking impact. A hybrid finite segment/finite element model and an experiment are presented for the deploy-ment system. The flexible beam components in the system are modelled with the finite segments connected by massless beam elements, wherein the finite segments describe the inertia of the large rotation flexible beam and the massless elastic elements describe the elas-ticity of the flexible beam by taking the advantage of small deformation in the relative co-ordinate system. To model the internal impacts in the articulate joints due to clearances, a continuous contact force model of locking joint is also proposed. The governing differential–algebraic equations of the system are established by the Newton–Euler method with Lagrange multipliers and are solved with the method of generalized co-ordinate partitioning. To accelerate the numerical integration, a “longitudinal constraint” is suggested to alleviate the stiff problem of the dynamic equations. In addition, a physical model of the deployment system is constructed. The deployment is released by the compressed springs in the joints. A position measuring system of linear CCD cameras is used to measure the large displacement of the system. Correlations between the mathematical model and the experiments are also presented. Reasonable results are obtained.

Delamination energy release rates under thermal loading in fiber-reinforced composite laminates

Free-edge delaminations of fiber-reinforced composite laminates under thermal loading are theoretically investigated. The weak form equilibrium equations are derived for a quasi-three-dimensional problem of laminates and an associated finite element method is used. The strain energy release rate due to the delamination growth is calculated from the finite element method and a newly developed simplified method which is an extension of the method formerly developed by the authors for laminates under mechanical loading. Attention is paid to the longitudinal constraint conditions of laminates, which have significant effects on the energy release rate. Numerical examples are shown for ( 90° 0° ) s cross-ply and ( 45° -45° ) s angle-ply laminates.

An experimental test of the theory of waves in fluid-filled deformable tubes

It seems that no treatment of pulsating flow in deformable tubes is complete without a reference to the work of Womersley (1955) which for an infinitely long tube deals with the waves of axismmetric transverse motion and of longitudinal motion of the walls. This theory has so far been subjected to experimental test only for tethered tubes in which longitudinal wall motion is absent.A series of measurements of the longitudinal motion has been made on horizontal water-filled latex tubes suspended by an array of strings so that there is minimal longitudinal constraint except at the ends, which are fixed. One end of the tube is driven by oscillating flow produced by a piston; the other end is closed. Theory and experiment agree when the tube is long provided an entrance length greater than a wavelength is included. Tubes which are short enough for reflection from the closed end to be significant present a more complicated problem. It is found that in the entrance length the theory of Womersley cannot be applied. A more refined theory is required which takes into account a distributed end constraint more completely than as a simple boundary condition.Experiments on tethered tubes in which longitudinal wall motion is absent are also presented. These serve to demonstrate that the theory for such tubes agrees with measurements without any appreciable end effect and also shows that the small viscoelasticity of the latex rubber is correctly included.

Pulsatile flow in arteries with external restraint of visco-elastic tissue

The presence of a longitudinal constraint must be conceived physiologically as due largely to the connective tissue attachments on the outside of the artery. Living tissues are viscoelastic bodies. In order to analyse the effect of external viscoelastic tissue to pulsatile flow in arteries, in this paper the external connective tissue of artery will be considered as a Voigt visco-elastic body, and the expressions of pulse wave velocity and the velocity of pulsatile flow will be found by the velocity of pulsatile flow will be found by the blood motion equations (Navier-Stokes equation) as well as wall motion equations (Lamb equation). The results of free elastic tube[4] and those of external elastic restraint[6] by Womersley can be considered as a particular case and can be covered in this paper.

Hemodynamic Flow in Anisotropic, Viscoelastic Thick-Wall Vessels

Hemodynamic flow in anisotropic, viscoelastic thick-wall vessels is analyzed. For small amplitude harmonic waves, the wavelengths of which are large compared to the vessel radius, the fluid motion is governed by the linearized form of the Navier-Stokes equations and the vessel motion is described by the classical Navier equations for solids. Compressible and incompressible transversely isotropic vessels with frequency dependent material moduli are considered. Longitudinal constraints are also incorporated. The quantities calculated are: the velocities of propagation, transmission per wavelength, fluid impedance, and the displacements and stresses at the fluid-vessel interface. The results indicate that the earlier anisotropic analyses, which incorporate membrane or thick shell theories, agree qualitatively with the present thick-wall analysis. However, quantitative differences among the analyses do occur, especially as the compressibility of the vessel material decreases. For the thick-wall analysis, the effects of anisotropy on the various quantities of interest are established. In particular, it is shown that the fluid impedance is relatively insensitive to the degree of anisotropy, but the resistance and inductance are very sensitive to anisotropy at the high and low values of frequency respectively. In general, anisotropy significantly affects the first mode transmission per wavelength and second mode phase velocity. The displacements and stresses at the fluid-vessel interface are also altered by anisotropy. In addition, the arterial system was found to be essentially independent of moderate variations in the axial shear modulus of the material. Furthermore, it is demonstrated that the degree of viscoelasticity associated with the vessel material substantially alters the transmission per wavelength but affects the phase velocity to a much lesser degree. For the suggested value of the spring parameter associated with the longitudinal constraint, it is found that the additional mass and the viscous parameters have little effect on the system behavior. The overall effect of the longitudinal constraint is to completely subdue the second mode of transmission, increase the first mode phase velocity, decrease the first mode transmission per wavelength and axial displacement, and to increase the modulus and decrease the phase of the first mode fluid impedance. In addition to confirming the importance of anisotropy, viscoelasticity, and the longitudinal constraint, the investigation demonstrates that an appropriate thick-wall analysis is required in order to adequately describe the fluid-vessel behavior.

A Study of the Effects of Cyclic Thermal Stresses on a Ductile Metal

Abstract The results of a study of cyclic strain and fatigue failure arising from cyclic thermal stresses are reported. By means of a test apparatus described in a companion paper, a cyclic temperature is imposed on a thin tubular test specimen subjected to complete longitudinal constraint. Hence, the cyclic strain is the independent variable. The following studies are reported: (a) Effect of thermal-stress cycling on strain hardening and life-to-failure for a fixed mean temperature, (b) effect of degree and kind of previous cold work on strain hardening and cycles-to-failure, (c) effect of mean temperature on thermal-stress cycling, (d) effect of period of cycle on cycles-to-failure, and (e) effect of prior strain cycling on stress-strain characteristics. The significance of factors such as hysteresis, Bauschinger effect, strain hardening, strain aging, and fatigue-crack formation is discussed, and a mechanism is described to relate these factors. Evidence is presented to show that strain hardening is not an important factor in the problem. The concept of total plastic strain is discussed.