The second-order nonlinear transport illuminates a frequency-doubling response emerging in quantum materials with a broken inversion symmetry. The two principal driving mechanisms, the Berry ...curvature dipole and the skew scattering, reflect various information including ground-state symmetries, band dispersions, and topology of electronic wave functions. However, effective manipulation of them in a single system has been lacking, hindering the pursuit of strong responses. Here, we report on the effective manipulation of the two mechanisms in a single graphene moiré superlattice, AB-BA stacked twisted double bilayer graphene. Most saliently, by virtue of the high tunability of moiré band structures and scattering rates, a record-high second-order transverse conductivity ∼ 510 μm S V–1 is observed, which is orders of magnitude higher than any reported values in the literature. Our findings establish the potential of electrically tunable graphene moiré systems for nonlinear transport manipulations and applications.
A material model to predict kink-band formation and growth under a 3D stress state is proposed. 3D kinking theory is used in combination with a physically based constitutive law of the material in ...the kink-band, accounting for friction on the microcracks of the damaged material. In contrast to existing models, the same constitutive formulation is used for fibre kinking and for the longitudinal shear and transverse responses, thereby simplifying the material identification process. The full collapse response as well as a crush stress can be predicted. The model is compared with an analytical model, a micromechanical finite element analysis and crushing tests. In all cases the present model predicts well the different stages of kink-band formation and crushing.
Recent Italian earthquakes have shown the seismic vulnerability of many typical historical masonry churches characterized by one nave and wooden roofs. Under transverse earthquake, the nave ...transverse response of this kind of churches can be influenced by the geometrical and material features. To increase the seismic performance, strengthening interventions aimed to pursue the global box-behavior by the realization of dissipative roof-structure represent a valid strategy, especially to avoid out-of-plane mechanisms. In this way, the roof structure must be able to represent a tool for the damped rocking of the perimeter walls. Cross-laminated timber (CLT) panels with calibrated metal connections have been recently adopted in experimental tests as a valid solution to obtain a roof-diaphragm with ductile behavior, satisfying the conservative restoration criteria at the same time. In this paper, after a description of the numerical approach for the damped rocking mechanism for one nave configuration church, the effectiveness of different CLT based roof-diaphragms in the nave transverse response is investigated for four historical churches. The seismic responses are performed by comparative dynamic nonlinear analyses and the results are shown in terms of displacements and shear actions transferred to the façade. The influence of the geometrical features of the churches on the nave transversal response is deepened by sensitivity analyses with the aim to predict the displacements and shear variations under the same earthquake excitation.
Multiple shaking table tests on an integral long-span cable-stayed bridge model were carried out to study the transverse response of pile group foundations. An elaborate bridge model was fabricated ...according to an assumed bridge with a total length of 2672 m and a geometric similarity ratio of 1/70. The superstructure of the bridge model consisted of a bridge girder, cables, two transition piers, four auxiliary piers and two pylons. The substructure of the model consisted of eight groups of piles embedded in synthetic soil. Accelerations, displacements and bending moments of the piles that supported the transition piers, auxiliary piers and pylons, respectively, were analyzed when the bridge was excited uniformly and nonuniformly in the transverse direction. The nonuniform excitation test was implemented by inputting the same motion to different shaking tables at different times. Three types of earthquake waves with different predominant frequencies were applied to the integral bridge model from low to high intensity. The test results indicated that distinct differences arose between the motions at the top of the pile groups supporting different parts of the superstructure despite the integral bridge model being subjected to uniform excitation. The large displacement difference between pile groups may be one of the origins of damage or even collapse of the superstructure. The amplification ratio of acceleration at the top of the pile group supporting the transition piers increased when the bridge model was excited by waves of low predominant frequency with increasing intensity. The transfer functions of accelerations (Fourier spectra of output accelerations over that of shaking table accelerations) at the top of the pile groups supporting the auxiliary piers were bimodal, which is different from the results of shaking table tests simulating the superstructure with a single degree of freedom (SDOF) system, in which only unimodal transfer functions can be obtained. The influence of the wave passage effect on the seismic response of the pile groups is detectable when the bridge model is excited longitudinally, while the influence is undetectable when the bridge model is excited transversely.
•An integral bridge model including superstructure and pile groups was fabricated.•The acceleration of piles may rise at faster rate with increasing input intensity.•Transfer functions of acceleration for pile group under auxiliary piers are bimodal.•The motions of pile groups under different parts of the superstructure are different.
This study focuses on the nonlinear vibration of a small-size beam hosted in a high-speed moving structure. The equation of the beam's motion is derived using the coordinate transformation. The ...small-size effect is introduced by applying the modified coupled stress theory. The equation of motion involves quadratic and cubic terms due to mid-plane stretching. Discretization of the equation of motion is achieved via the Galerkin method. The impact of several parameters on the non-linear response of the beam is investigated. Bifurcation diagrams are used to investigate the stability of the response, whereas softening/hardening characteristics of the frequency curves are used as an indication of nonlinearity. Results indicate that increasing the magnitude of the applied force tends to signify the nonlinear hardening behavior. In terms of the periodicity of the response, at a lower amplitude of the applied force, the response appears to be a one-period stable oscillation. Increasing the length scale parameter, the response moves from chaotic to period-doubling to the stable one-period response. The impact of the axial acceleration of the moving structure on the stability as well as on the nonlinearity of the response of the beam is also investigated.
In this study, vibration characteristics of a tapered laminated thick composite plate have been investigated using finite element method by including the shear deformation and rotary inertia effects. ...The governing differential equations of motion of a tapered laminated thick composite plate are presented in the finite element formulation based on first-order shear deformation theory for three types of taper configurations. The effectiveness of the developed finite element formulation in identifying the various dynamic properties of a tapered laminated thick composite plate is demonstrated by comparing natural frequencies evaluated using the present FEM with those obtained from the experimental measurements and presented in the available literature. Various parametric studies are also performed to investigate the effect of taper configurations, aspect ratio, taper angle, angle ply orientation and boundary conditions on free and forced vibration responses of the structures. The comparison of the transverse free vibration mode shapes of the uniform and tapered composite plates under various boundary conditions is also presented. The forced vibration response of a composite plate is investigated to study the dynamic response of tapered composite plate under the harmonic force excitation in various tapered configurations. It is concluded that the dynamic properties of laminated thick composite plates could be tailored by dropping off the plies to yield various tapered composite plate.
This study investigates the dynamic properties of the thickness tapered laminated composite plate. The governing differential equations of motion of the various configurations of a thickness tapered ...composite plate are presented in the finite element formulation using classical laminated plate theory. The validity of the developed finite element formulation is demonstrated by comparing the natural frequencies evaluated using the present finite element method with those derived from the experimental measurements and presented in available literature. Various parametric studies are also performed to investigate the effect of taper configuration, aspect ratio, taper angle and ply orientation on free vibration responses of the structures. The comparison of the free vibration mode shapes of uniform and various tapered configurations of tapered laminated composite plates are also presented. Influences of taper angle on the free vibration fundamental mode shapes under various boundary conditions and various ply configurations are also presented. The forced vibration response of a composite plate is also investigated to study the dynamic response of tapered composite plate under the harmonic force excitation in various tapered configurations. It is concluded that the dynamic properties of a composite plate could be tailored by dropping of the plies to yield various tapered composite plate.
The Sutong Bridge in China opened to traffic in 2008, and is an arterial connection between the cities of Nantong and Suzhou. It is a cable-stayed bridge with a main span of 1,088 m. Due to a tight ...construction schedule and lack of suitable seismic devices at the time, fixed supports were installed between the piers and the girder in the transverse direction. As a result, significant transverse seismic forces could occur in the piers and foundations, especially during a return period of a 2500-year earthquake. Therefore, the piers, foundations and fixed bearings had to be designed extraordinarily strong. However, when larger earthquakes occur, the bearings, piers and foundations are still vulnerable. The recent rapid developments in seismic technology and the performance-based design approach offer a better opportunity to optimize the transverse seismic design for the Sutong Bridge piers. The optimized design can be applied to the Sutong Bridge(as a retrofit), as well as other bridges. Seismic design alternatives utilizing viscous fluid dampers(VFD), or friction pendulum sliding bearings(FPSB), or transverse yielding metallic dampers(TYMD) are thoroughly studied in this work, and the results are compared with those from the current condition with fixed transverse supports and a hypothetical condition in which only sliding bearings are provided on top of the piers(the girder can move "freely" in the transverse direction during the earthquake, except for frictional forces of the sliding bearings). Parametric analyses were performed to optimize the design of these proposed seismic devices. From the comparison of the peak bridge responses in these configurations, it was found that both VFD and TYMD are very effective in the reduction of transverse seismic forces in piers, while at the same time keeping the relative transverse displacements between piers and the box girder within acceptable limits. However, compared to VFD, TYMD do not interact with the longitudinal displacements of the girder, and have simpler details and lower initial and maintenance costs. Although the use of FPSB can also reduce seismic forces, it generally causes the transverse relative displacements to be higher than acceptable limits.
A new mathematical model and its analytical solution for the analysis of the stress–strain state of a linear elastic beam cracked in flexure and strengthened with plates on its lateral sides is ...presented. Both the longitudinal and the transversal interactions at the side plate/beam interface are considered. Linear behaviour of the contact connection is assumed. The method is based upon the linearised planar beam theory of Reissner. The weakening of the beam induced by the flexural crack is modelled conventionally as a rotational spring. The suitability of the theory is demonstrated in a case presentation involving the comparison between analytical results of the present beam (one-dimensional) model, the experiments and the numerical results of a full three-dimensional solid model created in the LUSAS finite element analysis software. An excellent agreement between the results is observed and the proposed formulation is found to be accurate and reliable. Finally, the solution is employed in an engineering analysis, discussing the effects of the material and the geometric properties of selected characteristic cases of the observed beams on the static and kinematic quantities, including the boundary conditions of the side plates, the longitudinal and the transversal stiffness of the connection, the size of the cracks, the span of the beam, and the length and the stiffness of the side plates. For the cracked cantilever beam, a substantial effect of any of these parameters is found. In contrast, for the cracked two-span continuous beam, only the effect of the stiffness of the side plates and the effect of the length of the beam spans are noticeable.
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