Search

According to the nonlocal theory, the dynamic instability and vibration of functionally graded (FG) porous sandwich nanobeams resting on a visco-elastic foundation under axial harmonic load are studied. In this paper the Timoshenko and nonlocal continuum theory are employed to take shear deformation, rotational bending and small-scale effects into account. The governing equations of motion are extracted using the nonlinear Von-Karman, and Hamilton approaches. Then, to turn the partial differential equations (PDEs) into ordinary differential equations (ODEs) in the case of equations of motion, the method of Galerkin is employed, followed by the use of the multiple time scale method to solve the resulting equations. According to the results of this study, it can be claimed that the porosity ratio is more effective than porosity distribution and nonlocal parameters on the amplitude response and dynamic instability regions. Moreover, to examine thermal increments, foundation characteristics, slenderness, and thickness ratios, the bifurcation diagrams are drawn and discussed. It is found that foundation and geometric characteristics are of the highest significance in the nonlinear response of the Timoshenko nanobeams. The main intention of this study is to present a holistic idea about the porous materials used in sandwich structures which can be used in many composite structures in aircraft and automobiles. [ABSTRACT FROM AUTHOR]

Steel plate shear walls (SPSWs) often need to accommodate rectangular openings in their infill plates. When subjected to lateral loadings, such as wind and earthquake, unstiffened SPSWs with rectangular openings may experience large deformations around the openings. This paper presents a stiffener layout to limit the deformations around the rectangular openings in the SPSW system. The effectiveness of the proposed stiffener layout is investigated by conducting experimental tests on two one-third-scale single-story SPSWs with rectangular openings at the center of the infill plates. The two specimens have the same aspect ratio but have different rectangular opening sizes. To prevent deformations around the rectangular openings, the infill plates of the two test specimens are stiffened with the proposed stiffener layout. Quasi-static cyclic loading tests are performed on the specimens, and the deformations around the openings are measured at different loading stages. Tests showed that the proposed stiffener layout can successfully restrain the deformations around the rectangular openings. The specimens also showed stable hysteresis curves and good energy-dissipation capacity. To further examine the inelastic performance of the proposed stiffener layout, finite-element analysis of stiffened SPSWs is conducted. Seismic analyses are also performed for 4-story stiffened and unstiffened SPSWs with rectangular openings to investigate the seismic response of SPSWs with the proposed stiffener layout around the openings. Seismic analyses showed that the proposed stiffener layout around the rectangular openings can prevent the out-of-plane and in-plane deformations around the openings in the SPSW system. [ABSTRACT FROM AUTHOR]

This article studies parametric vibration and dynamic instability of a rectangular and symmetric magnetostrictive sandwich composite plate (MSCP) on a visco-Pasternak medium. The MSCP consists of three layers; a magnetostrictive layer considers the core and composites as its upper and lower faces. The MSCP subjected to temperature change, parametrically exciting force, and magnetic load is studied with consideration to geometrical von Karman nonlinearity. Based on the energy method and first shear deformation theory (FSDT), Hamilton's principle is used to achieve the system's governing equations and boundary conditions. In the next step, the partial differential equation is transformed into ordinary differential equations by applying the Galerkin technique. Then the equation of motion is solved using the multiple-scale method. Numerical results illustrate the stability of the sandwich plate is significantly related to the magnetostrictive parameters. In addition, the effects of significant parameters, such as the effect of amplitude response and parametric excitation or detuning parameter, coupled with the effect of foundation, thickness ratio, aspect ratio, and temperature increment on vibration characteristics, bifurcation points behavior and stability of the systems are charted, plotted and discussed. The innovation of this article is the use of magnetostrictive material in sandwich plates and the development of its mathematical relationships. It is anticipated that the results of this research can contribute to the development of future smart structural applications subjected to in-plane axial forces. [ABSTRACT FROM AUTHOR]

During the last 3 decades interest has grown globally in the application of ductile steel plate walls (DSPWs) (or steel plate shear walls) for building lateral load resistance. The supporting theory has evolved from both analytical and experimental research conducted in several countries around the world. The advantages of using DSPWs as the lateral force resisting system in buildings include stable hysteretic characteristics, high plastic energy absorption capacity, and enhanced stiffness, strength and ductility. A significant number of experimental and analytical studies have been carried out to establish analysis and design methods for such lateral resisting systems. Despite these efforts there is still a need for a general analysis and design methodology that not only accounts for the interaction of the plates and the framing system but also can be used to better understand the linear and nonlinear behavior of different DSPW configurations. These configurations include DSPWs with thin or thick steel plates, and with or without stiffeners and openings. In this paper an analytical model of the DSPW that responds to this need and characterizes the structural behavior of these configurations is presented and discussed. The proposed model provides a good understanding of how the different components of the system interact, and is able to properly represent the system's overall hysteretic characteristics, which can be readily incorporated in practical nonlinear analyses of buildings with DSPWs. The effectiveness of the method is demonstrated by comparing the predicted response with results from experimental studies performed by different researchers. DOI: 10.1061/(ASCE)0733-9445(2005)l31:6(878) CE Database subject headings: Steel plates; Shear walls; Shear properties; Cyclic tests: Hysteresis; Energy dissipation; Shear strength.

SUMMARY Yielding damped braced core (YDBC) consists of a central-framed steel plate (damper) located at the intersection of X bracing members. In severe earthquakes, the damper would yield and will result in spindle hysteresis cycles. YDBC is capable of dissipating large amounts of energy. In the present paper, an investigation is made on how individual components of the system affect the overall strength and stiffness of the system. The results are verified by a sample problem. It is calculated that the stiffness of braces, as well as the central core, play a major role in system overall stiffness. And finally, using properly designed braces, the energy absorption mechanism could be transferred to the central core. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To improve buckling stability and to prevent early elastic buckling of infill plates, vertical and horizontal plate stiffeners are designed for steel plate shear wall (SPSW) systems. Furthermore, effective design of stiffeners for SPSW systems results in improved structural behavior, such as increase of stiffness, capacity and energy absorption. In this paper, the effect of stiffeners is studied on SPSW structural behavior and consequently a rational method is proposed to determine the minimum required moment of inertia for stiffeners resulting in local buckling mode of the infill plate. The proposed requirement is then compared to results obtained from tests previously conducted, as well as those gained from finite element (FE) analyses performed for this study. [ABSTRACT FROM AUTHOR]