Showing papers on "Bending moment published in 2009"

A semi‐discrete shell finite element for textile composite reinforcement forming simulation

Abstract: A triangular shell element for the simulation of textile composite reinforcements forming is proposed. This element is made up of unit woven cells. The internal virtual works are added on all woven cells of the element. They depend on tensions, in-plane shear and bending moments that are directly those given by the experimental tests that are specific to textile composite reinforcement. The element has only displacement degrees of freedom; the bending curvatures are obtained from the displacement of the neighbouring elements. A set of example shows the efficiency of the approach and the relative roles of the tensile, in-plane shear and bending rigidities. Especially their influence on the appearance and the development of wrinkles in draping and forming tests is analysed. Copyright © 2009 John Wiley & Sons, Ltd.

Mitigation of Higher Mode Effects in Base-Rocking Systems by Using Multiple Rocking Sections

Abstract: Base-rocking systems have been proposed as a way to limit the seismic forces experienced by a structure without accepting structural damage. However, structural forces can increase significantly, even when the base moment is limited, because of higher mode effects. This article suggests that these effects may be substantially reduced by designing to allow rocking to occur at multiple locations over the height of a base-rocking system. This is confirmed by a statistical study of the response of 24 systems of varying height and joint configuration to two suites of 20 earthquakes, as well as by a case study of the response of five 12-story systems designed using a displacement-based procedure. The bending moment envelope above the base of the wall is shown to be greatly reduced by providing multiple rocking sections, while the peak displacements do not increase in magnitude or in variability.

Finite element modelling of dielectric elastomer minimum energy structures

Abstract: This paper presents an experimentally validated finite element model suitable for simulating the quasi-static behaviour of Dielectric Elastomer Minimum Energy Structure(s) (DEMES). A DEMES consists of a pre-stretched Dielectric Elastomer Actuator (DEA) adhered to a thin, flexible frame. The tension in the stretched membrane causes the frame to curl up, and when a voltage is applied, the frame returns to its initial planar state thus forming a useful bending actuator. The simulation method presented here incorporates a novel strain energy function suitable for simulating general DEA actuator elements. When compared against blocked force data from our previous work, the new model provides a good fit with an order of magnitude reduction in computational time. Furthermore, the model accurately matched experimental data on the free displacement of DEMES formed with non-equibiaxially pre-stretched VHB4905 membranes driven by 2500 V. Non-equibiaxially pre-stretching the membranes allowed control of effective frame stiffness and bending moment, this was exploited by using the model to optimise stroke at 2500 V in a hypothetical case study. Dielectric constant measurements for non-equibiaxially stretched VHB4905 are also presented.

Bending of functionally graded cantilever beam with power-law non-linearity subjected to an end force

Abstract: A realistic beam structure often exhibits material and geometrical non-linearity, in particular for those made of metals. The mechanical behaviors of a non-linear functionally graded-material (FGM) cantilever beam subjected to an end force are investigated by using large and small deformation theories. Young's modulus is assumed to be depth-dependent. For an FGM beam of power-law hardening, the location of the neutral axis is determined. The effects of depth-dependent Young's modulus and non-linearity parameter on the deflections and rotations of the FGM beams are analyzed. Our results show that different gradient indexes may change the bending stiffness of the beam so that an FGM beam may bear larger applied load than a homogeneous beam when choosing appropriate gradients. Moreover, the bending stress distribution in an FGM beam is completely different from that in a homogeneous beam. The bending stress arrives at the maximum tensile stress at an internal position rather than at the surface. Obtained results are useful in safety design of linear and non-linear beams.

Simulation of the shaking table test of a seven-story shear wall building

Abstract: This paper presents the simulation of the nonlinear dynamic response of a full-scale seven-story reinforced concrete shear wall shaking table specimen under base excitations representing four earthquake records of increasing intensity. The study was motivated by the participation in the blind prediction contest of the shaking table specimen organized by University of California at San Diego (UCSD), NEES, and Portland Cement Association (PCA). Owing to the time constraints of the contest a relatively simple two-dimensional (2d) model was used for the shear wall specimen. In this model, the shear wall was represented by 2d beam-column elements with fiber discretization of the cross-section that account for the interaction of the axial force with the bending moment. Upon conclusion of the contest, the available experimental measurements permitted a thorough examination of the analytical results. While the measured data confirmed the excellent accuracy of the model predictions, some limitations also became apparent. The paper addresses the benefits and limitations of the selected modeling strategy and investigates the sensitivity of this type of model to parameter selection.

Kinematic response analysis of piled foundations under seismic excitation

Abstract: This paper presents the results of an extensive parametric study on single piles and pile groups embedded in a two-layer subsoil profile, and is aimed to evaluate kinematic bending moments developi...

Static Analysis of Single Walled Carbon Nanotubes (Swcnt) Based on Eringen’s Nonlocal Elasticity Theory

Abstract: Static analysis of carbon nanotubes (CNT) is presented using the nonlocal Bernoulli-Euler beam theory. Differential quadrature (DQ) method is used for bending analysis of numerical solution of carbon nanotubes. Numerical results are presented and compared with that available in the literature. Deflection and bending moment are presented for different boundary conditions. It is shown that reasonable accurate results are obtained

Inelastic axial-flexure-shear coupling in a mixed formulation beam finite element

Abstract: In this paper a beam element that accounts for inelastic axial-flexure–shear coupling is presented. The mathematical model is derived from a three-field variational form. The finite element approximation for the beam uses shape functions for section forces that satisfy equilibrium and discontinuous section deformations along the beam. No approximation for the beam displacement field is necessary in the formulation. The coupling of the section forces is achieved through the numerical integration of an inelastic multi-axial material model over the cross-section. The proposed element is free from shear-locking. Examples confirm the accuracy and numerical robustness of the proposed element and showcase the interaction between axial force, shear, and bending moment.

Liquefaction-induced lateral load on pile in a medium dr sand layer

Abstract: One-g shake-table experiments are conducted to explore the response of single piles due to liquefaction-induced lateral soil flow. The piles are embedded in saturated Medium Relative Density (Dr) sand strata 1.7–5.0 m in thickness. Peak lateral pile displacements and bending moments are recorded and analyzed by uniform and triangular pressure distributions. On this basis, the observed levels of pile bending moment upon liquefaction suggest a hydrostatic lateral pressure approximately equal to that due to the total overburden stress. Using the experimental data, comparisons with current recommendations are made, and the Showa Bridge case history is briefly assessed.

Cooling Performance of Arrays of Vibrating Cantilevers

Abstract: A piezoelectric fan is a cantilever beam whose vibration is actuated by means of a piezoelectric element. This element is typically bonded near the clamped end of the beam and induces a bending moment at the interface between the cantilever beam and the piezo element when a voltage is applied. For an alternating voltage, the beam is set into an oscillatory motion, which in turn creates motion in the surrounding fluid. This fluid motion has been shown to provide heat transfer enhancements with low power consumption in an otherwise quiescent region. These devices can also be configured to meet the geometric constraints of applications where the limited available volume might preclude the use of traditional cooling techniques. The fan design can be tailored to operate at frequencies, which are inaudible to the human ear. Due to these attractive features, piezoelectric fans have been investigated in the literature for practical cooling applications. Vibrating cantilever-type structures have been commonplace in engineering for decades. However, detailed studies of the motion induced in the surrounding fluid, and more importantly its effect on heat transfer, have only been recently undertaken. Flow field measurements around a cantilever vibrating in quiescent air at relatively small vibration amplitudes less than 3 mm peak-topeak tip vibration were obtained by Kim et al. 1. They observed a pair of counter-rotating vortices from each oscillation cycle. These vortices were shed from the fan tip as it passed the position of zero displacement. The maximum velocity occurred in the region between these two vortices and just beyond the cantilever tip, and was measured to be approximately four times the maximum tip velocity. Kimber et al. 2 experimentally measured the local heat transfer characteristics of piezoelectric fans and developed heat transfer correlations based on applicable dimensionless numbers. Numerical modeling of the fluid flow and heat transfer induced

Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay

Abstract: A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement.

Elastic stability of plates with circular and rectangular holes subjected to axial compression and bending moment

Abstract: In this paper linear buckling analyses of square and rectangular plates with circular and rectangular holes in various positions subjected to axial compression and bending moment are developed. The aim is to give some practical indications on the best position of the circular hole and the best position and orientation of rectangular holes in steel plates, when axial compression and bending moment act together. Two different orientations are considered for rectangular holes: holes with major dimension parallel to the vertical plate axis (RS holes) and major dimension parallel to horizontal plate axis (RL holes). The effect of bending moment on the stability of the plate is studied and some differences with respect to the uniform compression load case are shown. Some design suggestions on the best orientation of rectangular for stability purposes are given. The influence of dimension and position of perforations on linear buckling behaviour and, in particular, on buckling coefficient of the plate is observed. Some practical design formulations for the calculation of the buckling coefficient, taking into account (a) dimensions and shape (square and rectangular) of the plate, (b) dimensions and shape (circular and rectangular) of the hole, (c) position of the hole (centre in the “maximum” and in the “nodal” point), (d) orientation (RS and RL) of the rectangular hole, and (e) load configuration (uniform compression, combinations of axial compression and bending and pure bending) are finally proposed.

An analytical solution for the magneto-electro-elastic bimorph beam forced vibrations problem

Abstract: Based on the Timoshenko beam theory and on the assumption that the electric and magnetic fields can be treated as steady, since elastic waves propagate very slowly with respect to electromagnetic ones, a general analytical solution for the transient analysis of a magneto-electro-elastic bimorph beam is obtained. General magneto-electric boundary conditions can be applied on the top and bottom surfaces of the beam, allowing us to study the response of the bilayer structure to electromagnetic stimuli. The model reveals that the magneto-electric loads enter the solution as an equivalent external bending moment per unit length and as time-dependent mechanical boundary conditions through the definition of the bending moment. Moreover, the influences of the electro-mechanic, magneto-mechanic and electromagnetic coupling on the stiffness of the bimorph stem from the computation of the beam equivalent stiffness constants. Free and forced vibration analyses of both multiphase and laminated magneto-electro-elastic composite beams are carried out to check the effectiveness and reliability of the proposed analytic solution.