Effects Of Stiffness Ratio Research Articles

Seismic Response of Two-way Asymmetric building with Semi-Active Stiffness Damper Under Bi-Directional Excitations

This article presents a seismic response of a two-way asymmetric building installed with a semi-active stiffness damper (SASD). The seismic response analysis of asymmetric structure is studied in terms of peak responses subjected to bi-directional excitations. The responses are obtained by numerically solving the governing equation of motion using state-space method. The effect of stiffness ratio and lyapunov constant on peak response which includes lateral, torsional displacement, and acceleration. The responses of asymmetric controlled and uncontrolled systems are simulated through MATLAB. To study the effectiveness of dampers, the controlled response of the asymmetric system is compared with the corresponding uncontrolled response. The parametric study indicated that the semi-active stiffness damper is quite effective in reducing various responses. Furthermore, on the optimum value of stiffness ratio, effectiveness of semi-active stiffness damper is reduced for lateral and torsional acceleration.

Research on the Effect of Stiffness Ratio Between Frame and Core Tube on Seismic Response of Super High-rise Building Under Frequent Earthquake

The stiffness ratio of frame to core tube has an important influence on the seismic behavior of frame-core tube hybrid structure which is a high-rise building structure system widely used in the world. In this paper, nine models of concrete-filled steel tubular frame-concrete core tube super-high-rise hybrid structures with different stiffness ratios are established by using finite element method, and the effect of stiffness ratio on inter-story displacement angle, top displacement and base shear force of super high-rise buildings under frequent earthquakes is studied. The results show that, with the increase of stiffness ratio, the inter-story displacement angle, the top displacement and the base shear force change complicatedly, the maximum base shear force increase, and the maximum inter-story displacement angle and the maximum top displacement first increase then peak, and that the strengthening layer with outrigger obviously improves the deficiency of lateral stiffness caused by height. This study provides a reference for reasonable determination of stiffness ratio and optimization of structural seismic design.

Enhanced ride comfort using nonlinear seat suspension with high-static-low-dynamic stiffness

To attenuate the low-frequency vibration transmitted to the driver, a nonlinear seat suspension with high-static-low-dynamic stiffness is designed. First, the force and stiffness characteristics are derived. The nonlinear suspension can achieve the quasi-zero stiffness at the static equilibrium position when the structural parameters are properly designed. Then, a car-seat-human coupled model which consists of a quarter car model, a seat suspension, and a 4 degree-of-freedom human model is established to predict the biodynamic response of the driver. Finally, the isolation performance of the high-static-low-dynamic stiffness seat suspension under two typical road excitations is evaluated separately based on the numerical method. The effects of stiffness ratio, damping ratio, and vehicle speed on the ride comfort are investigated. The results showed that the nonlinear seat suspension outperforms the equivalent linear counterpart and can achieve the best ride comfort when the quasi-zero stiffness condition is satisfied.

Effective Negative Mass Nonlinear Acoustic Metamaterial with Pure Cubic Oscillator

Acoustic metamaterial, which can prohibit effectively the elastic wave propagation in the bandgap frequency range, has broad application prospects in the vibration and noise reduction areas. The Lindstedt–Poincaré method was utilized to analyze the dispersion curves of nonlinear metamaterial with a pure Duffing oscillator. The first-order perturbation solutions of acoustic and optical branches were obtained. Both the starting and cutoff frequencies of the bandgap are determined consequently. It was found that the soft/hard characteristics of pure Duffing oscillators could lead to the lower/upper movement of the starting and cutoff frequencies of the bandgap. By further researching the degraded linear system, the conclusion that actual nonlinear metamaterial bandgap region is wider than effective negative mass region is drawn and that both mass and stiffness ratio effect on the starting frequency is obtained. Effective positive mass can also lead to the vibration attenuation in bandgap. For nonlinear metamaterial, the translation effect of the external excitation amplitude on the bandgap range and the zero mass at the nonlinear bandgap cutoff frequency were discussed, and all above conclusion are identified by numerical analysis.

Residual displacement demands of conventional and dual oscillators subjected to earthquake ground motions characteristic of the soft soils of Mexico City

This paper presents a statistical evaluation of residual displacement (RDs) demands in conventional and dual single-degree-of-freedom (SDOF) oscillators subjected to a set of 220 earthquake ground motions recorded at soft soil sites of Mexico City. A dual SDOF oscillator represents a highly-dissipating energy system (e.g. buckling-restrained braces, BRBs) acting in parallel with a conventional system (e.g. flexible moment-resisting frames). To provide a context, RDs were normalised with respect to the corresponding: a) maximum transient displacements, and b) elastic spectral displacement. The effects of post-yield stiffness ratio (as affected by P-Δ effects), normalised period of vibration with respect to the predominant period of the ground motion, the type of hysteretic response, maximum displacement ductility, lateral strength ratio, type of transition (from elastic-to-plastic response), and damping ratio on normalised RDs were examined for the conventional oscillators. In addition, the effects of the stiffness ratio, lateral strength ratio, displacement ductility, post-yielding stiffness ratio, and type of hysteretic response of the primary and secondary parts of dual SDOF oscillators on normalised RDs were also evaluated. From the results of this investigation, it was observed that for dual SDOF systems the amplitude of normalised RDs is small when the primary part remains elastic. On the contrary, if the primary part exhibits inelastic response, normalised RDs might increase significantly and the post-yielding stiffness ratio of the secondary part plays a key role for constraining them (i.e. while a positive value reduces RDs significantly; a negative value is highly detrimental). Also, it was found that the type of hysteretic response of the primary part of a dual system has a significant effect on normalised RDs (e.g. it was found that a primary part with self-centring capacity, acting in parallel with a highly dissipation system (e.g. BRBs) as secondary part, is very effective for diminishing RDs). A discussion section is also offered to highlight the new findings of this study and differences on normalised RD demands between soft and stiff soils.

Effect of stiffness and thickness ratio of host plate and piezoelectric patches on reduction of the stress concentration factor

This paper focuses on the effects of stiffness ratio and thickness ratio on reducing stress concentration factor using piezoelectric patches in a rectangular plate with a hole, as a classical shape. Various locations of actuators and induction of positive/negative strains into the host plate are investigated and the best location of patches is presented. The study investigated the ratio effects and piezoelectric patches bounded on a rectangular host plate having various thicknesses and materials. Results show that the best position of actuators varies based on values of thickness and stiffness ratios of the host plate and piezoelectric patches. Also, the location of maximum stress concentration is transmitted from top and bottom of the hole to another point around the edge by changing the location of the piezoelectric actuators. To verify the results, some experimental tests are applied. The results show good agreement between the finite element analysis and experimental tests.

Effect of variable particle stiffness on force propagation and mechanical response of a composite granular material.

The force propagation and mechanical response are important for understanding the elasticity and deformation of a composite granular packings. In this paper, a 2D composite granular layers composed of particles with variable stiffness is proposed, and the effect of stiffness ratio between component particles on mechanical response is mainly considered. The results show that the decrease of stiffness ratio broadens the linear range of mechanical response and enhances the elasticity of the response in a composite granular system, showing a role similar with the friction in a monodisperse granular packings. Furthermore, a phase diagram for the crossover between a single-peaked and a double-peaked response is proposed, in which the critical stiffness ratio corresponding to the occurrence of the crossover decreases with the magnitude of external loading and increases with the friction. Finally, the microscopic mechanism of the crossover of the response is further discussed based on changes in contact network and force network.

Effect of Stiffness Ratio of Piecewise-Linear Spring on the Occurrence of Subharmonic Nonlinear Vibration in Automatic Transmission Powertrain

In the torque converter, a damper with a piecewise-linear spring is used to reduce the forced vibration, and the subharmonic vibration occurs when the spring restoring torque characteristics approach the switching point. This research analyzed the effect of stiffness ratio between the neighboring piecewise-linear springs on the occurrence of the subharmonic nonlinear vibration in automatic transmission powertrain. The powertrain is modeled with multi degree-of-freedom nonlinear system as an actual vehicle. The result shows higher value of the stiffness ratio between the neighboring springs creates larger value of the subharmonic vibration.

Performance Analysis of Functionally Graded Coatings in Contact with Cylindrical Rollers

This work presents finite element analysis (FEA) and results for rolling contact of a cylindrical roller on an elastic substrate coated by functionally graded material (FGM). The rolling process and the graded coating material property and layers arrangement are modeled using finite element codes which lead to a new methodology. This novel methodology provides a trend in determining surface contact stresses, deformations, contact zones, and energy dissipation through the contact area. Effects of stiffness ratio, friction, and exponentially variation of material property on the contact stresses and deformations are studied. Some of the results are verified with analytical solutions. The study results may be beneficial in graded coated cylindrical components analysis against rolling contact failure and wear.

Analytical Solution of Interface Effect on the Strength of Combined Model Composed of Different Geologic Bodies

According to the special combined structure of surrounding rock in western mining area of China, a micromechanical model with variable parameters containing contact interface was proposed firstly. Then, the derived stresses in coal and rock near the interface were analyzed on the basis of the harmonized strain relation, and the analytical solutions with respect to stress states near the interface were drawn up. The triaxial compressive strength of coal and rock was further determined in case the contact interface was in the horizontal position. Moreover, effects of stiffness ratio, interface angle, and stress level on the strength of two bodies near the contact area were expounded in detail. Results indicate that additional stresses which have significant effect on the strength of combined model are derived due to the adhesive effect of contact interface and lithological differences between geologic bodies located on both sides. The interface effect on the strength of combined body is most associated with the stiffness, interface angle, and the stress level. These conclusions are also basically valid for three-body model and even for the multibody model and lay important theory foundation to guide the stability study of soft strata composed of different geologic bodies.

Dynamic Analysis of Slanting Type Five-Span Continuous CFST Arch Bridge without Wind Tied-Bracing

The concrete-filled steel tube (CFST) member has many advantages compared with the ordinary structural member made of steel or reinforced concrete. Continuous confinement provided by the steel tubes prevents excessive spalling of concrete and the concrete filled inside the steel tubes prohibits local inward buckling of the steel tube wall. This paper presents the dynamic response of a slanting type CFST arch bridge without wind tied-bracing. Effect of stiffness ratio between slanting arch and vertical arch on seismic performance was discussed.

VERTICAL VIBRATIONS OF BASE ISOLATED MACHINEFOUNDATIONS

Vibration of base isolated machine foundations has been studied using the ScaledBoundary Finite Element Method (SBFEM) and the cone model method. Thedynamic stiffness of soil supporting rigid massless foundation was determined. Thisstiffness is of complex value. The real part represents the reflected energy of therestoring and inertial forces while the imaginary part represents the energy dissipatedwithin the endless extent of the soil as a geometric damping. The effect of geometricand material properties of soil upon the real and imaginary parts of the dynamicstiffness was determined and represented in terms of dimensionless charts for thefrequency range of interest. Results have shown that increasing the embedment ratiohas a significant effect on the dynamic stiffness, it increases the dynamic stiffnessconsiderably. The effect of stiffness ratio(stiffness of isolator/ stiffness of soil) wasdemonstrated for isolated machine foundations. The use of soft isolators reduces thedynamic response of foundation and the soil reaction

On some aspects of pin-loaded laminates

Some aspects of pin loaded laminates, including basic kinematics related to the contact angle and moving boundary, validity and applicability of cosine distribution of contact stress, effects of stiffness ratios as well as clearance and friction are presented. Numerical results on the basis of a previously developed direct boundary element procedure, with a refined and improved computational algorithm with additional capabilities are given and used for discussing various aspects of pin-loaded orthotropic laminates. Empirical formulas based on generated computer results are suggested.

Discussion of “ Pipe/Soil Stiffness Ratio Effect on Flexible Pipe Buckling Threshold ” by Kenneth K. Kienow and Robert C. Prevost (March, 1989, Vol. 115, No. 2)

Discussion of “ <i>Pipe/Soil Stiffness Ratio Effect on Flexible Pipe Buckling Threshold</i> ” by Kenneth K. Kienow and Robert C. Prevost (March, 1989, Vol. 115, No. 2)

Closure to “ Pipe/Soil Stiffness Ratio Effect on Flexible Pipe Buckling Threshold ” by Kenneth K. Kienow and Robert C. Prevost (March, 1989, Vol. 115, No. 2)

Closure to “ <i>Pipe/Soil Stiffness Ratio Effect on Flexible Pipe Buckling Threshold</i> ” by Kenneth K. Kienow and Robert C. Prevost (March, 1989, Vol. 115, No. 2)

Pipe/Soil Stiffness Ratio Effect on Flexible Ipe Buckling Threshold

This paper reports a study of the buckling aspect of various defects such as flattening or squaring of pipe. The paper discusses pipe stiffness definitions, buckling number, Spangler's model instability, changes in curvature with deflection, time factor, the Luscher model, pipe shape effects on buckling, buckling data, and failure data plot. None of the current buckling models can be used with any degree of reliability to predict the buckling resistance of a flexible pipe because the models allow very weak pipes which actually buckle in the field. There is evidence that a minimum pipe stiffness is required to prevent buckling, through apportioning the pipe stiffness to the loading. The principal determining buckling factor for low stiffness may be the installation procedure which often results in shape defects.