Dynamic Stiffness and Damping of Piles

1974 ◽  
Vol 11 (4) ◽  
pp. 574-598 ◽  
Author(s):  
Milos Novak
Keyword(s):  
Dynamic Response ◽  
Closed Form ◽  
Linear Elasticity ◽  
Analytical Approach ◽  
Dynamic Stiffness ◽  
Vertical Plane ◽  
Shallow Foundations ◽  
Pile Head ◽  
Pile Interaction ◽  
Stiffness And Damping

Dynamic response of footings and structures supported by piles can be predicted if dynamic stiffness and damping generated by soil–pile interaction can be defined. An approximate analytical approach based on linear elasticity is presented, which makes it possible to establish the dimensionless parameters of the problem and to obtain closed-form formulas for pile stiffness and damping. All components of the motion in a vertical plane are considered; that is, horizontal as well as vertical translations and rotation of the pile head. The stiffness and damping of piles are defined in such a way that the design analysis of footings and structures resting on piles can be conducted in the same way as is applied in the case of shallow foundations.

Foundations for shock-producing machines

1983 ◽  
Vol 20 (1) ◽  
pp. 141-158 ◽  
Author(s):  
M. Novak
Keyword(s):  
Analytical Approach ◽  
Response Prediction ◽  
Shallow Foundations ◽  
Pile Foundations ◽  
Complex Eigenvalue ◽  
Eigenvalue Approach ◽  
Energy Consideration ◽  
Stiffness And Damping

The principal criteria for the design of hammer foundations are specified and the methods of defining stiffness and damping constants for shallow foundations and pile foundations are reviewed. An analytical approach to the prediction of damped vibration is presented. The incorporation of damping is based on an energy consideration and verified by comparison with results obtained using the complex eigenvalue approach. The inclusion of damping makes the response prediction more realistic and may prevent considerable overestimation of the response and overdesign of the foundation. Keywords: damping, dynamics, foundations, hammers, shock, vibration.

An Exact Solution to the Free Vibration Analysis of a Uniform Timoshenko Beam Using an Analytical Approach

2021 ◽  
Author(s):  
Valentin Fogang
Keyword(s):  
Exact Solution ◽  
Free Vibration ◽  
Closed Form ◽  
Timoshenko Beam ◽  
Vibration Analysis ◽  
Analytical Approach ◽  
Dynamic Stiffness ◽  
Free Vibration Analysis ◽  
Winkler Foundation ◽  
Mass System

This study presents an exact solution to the free vibration analysis of a uniform Timoshenko beam using an analytical approach, a harmonic vibration being assumed. The Timoshenko beam theory covers cases associated with small deflections based on shear deformation and rotary inertia considerations. In this paper, a moment-shear force-circular frequency-curvature relationship was presented. The complete study was based on this relationship and closed-form expressions of efforts and deformations were derived. The free vibration response of single-span systems, as well as that of spring-mass systems, was analyzed; closed-form formulations of matrices expressing the boundary conditions were presented and the natural frequencies were determined by solving the eigenvalue problem. Systems with intermediate mass, spring, or spring-mass system were also analyzed. Furthermore, first-order dynamic stiffness matrices in local coordinates were derived. Finally, second-order analysis of beams resting on an elastic Winkler foundation was conducted. The results obtained in this paper were in good agreement with those of other studies.

scholarly journals Finite Element Steady-State Vibration Analysis Considering Frequency-Dependent Soil-Pile Interaction

2019 ◽  
Vol 9 (24) ◽  
pp. 5371 ◽  
Author(s):  
Seung-Han Song ◽  
Sean Seungwon Lee
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Dynamic Stiffness ◽  
Time History ◽  
Full Spectrum ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
Pile Interaction ◽  
Soil Foundation ◽  
Stiffness And Damping

The vibration response of equipment foundation structures is not only affected by the structural stiffness and mass, but also greatly influenced by the degree of a soil-foundation structural interaction. Furthermore, the vibratory performance of equipment foundation structures supported by pile systems largely depends on the soil-pile dynamic stiffness and damping, which are variable in nature within the speed range that machines operate at. This paper reviews a method for evaluating effective soil-pile stiffness and damping that can be computed by Novak’s method or by commercial software (DYNA6, University of Western Ontario). A series of Finite Element (FE) time history and steady-state analyses using SAP2000 have been performed to examine the effects of dynamic soil-pile-foundation interaction on the vibration performance of equipment foundations, such as large compressor foundations and steam/gas turbine foundations. Frequency-dependent stiffness is estimated to be higher than frequency-independent stiffness, in general, and, thus, affects the vibration calculation. This paper provides a full-spectrum steady-state vibration solution, which increases the reliability of the foundation’s structural design.

scholarly journals Fast simulation of railway bridge dynamics accounting for soil–structure interaction

2021 ◽  
Author(s):  
P. Galvín ◽  
A. Romero ◽  
E. Moliner ◽  
D. P. Connolly ◽  
M. D. Martínez-Rodrigo
Keyword(s):  
Dynamic Response ◽  
Soil Structure ◽  
Dynamic Stiffness ◽  
Computational Cost ◽  
Soil Structure Interaction ◽  
Fe Model ◽  
Structure Interaction ◽  
Railway Traffic ◽  
Soil Foundation ◽  
Stiffness And Damping

AbstractA novel numerical methodology is presented to solve the dynamic response of railway bridges under the passage of running trains, considering soil–structure interaction. It is advantageous compared to alternative approaches because it permits, (i) consideration of complex geometries for the bridge and foundations, (ii) simulation of stratified soils, and, (iii) solving the train-bridge dynamic problem at minimal computational cost. The approach uses sub-structuring to split the problem into two coupled interaction problems: the soil–foundation, and the soil–foundation–bridge systems. In the former, the foundation and surrounding soil are discretized with Finite Elements (FE), and padded with Perfectly Match Layers to avoid boundary reflections. Considering this domain, the equivalent frequency dependent dynamic stiffness and damping characteristics of the soil–foundation system are computed. For the second sub-system, the dynamic response of the structure under railway traffic is computed using a FE model with spring and dashpot elements at the support locations, which have the equivalent properties determined using the first sub-system. This soil–foundation–bridge model is solved using complex modal superposition, considering the equivalent dynamic stiffness and damping of the soil–foundation corresponding to each natural frequency. The proposed approach is then validated using both experimental measurements and an alternative Finite Element–Boundary Element (FE–BE) methodology. A strong match is found and the results discussed.

Dynamic response of cylindrical cavity to anti-plane impact load by using analytical approach

2014 ◽  
Vol 21 (1) ◽  
pp. 405-415 ◽  
Author(s):  
Chao-jiao Zhai ◽  
Tang-dai Xia ◽  
Guo-qing Du ◽  
Zhi Ding
Keyword(s):  
Dynamic Response ◽  
Cylindrical Cavity ◽  
Analytical Approach ◽  
Impact Load

Design and structural performance measurements of a novel multi-cantilever foil bearing

2014 ◽  
Vol 229 (10) ◽  
pp. 1830-1838 ◽  
Author(s):  
Kai Feng ◽  
Xueyuan Zhao ◽  
Zhiyang Guo
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Load ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Foil Bearing ◽  
Load Tests ◽  
Stiffness And Damping ◽  
Motion Amplitude

With increasing need for high-speed, high-temperature, and oil-free turbomachinery, gas foil bearings (GFBs) have been considered to be the best substitutes for traditional oil-lubricated bearings. A multi-cantilever foil bearing (MCFB), a novel GFB with multi-cantilever foil strips serving as the compliant underlying structure, was designed, fabricated, and tested. A series of static and dynamic load tests were conducted to measure the structural stiffness and equivalent viscous damping of the prototype MCFB. Experiments of static load versus deflection showed that the proposed bearing has a large mechanical energy dissipation capability and a pronounced nonlinear static stiffness that can prevents overly large motion amplitude of journal. Dynamic load tests evaluated the influence of motion amplitude, loading orientation and misalignment on the dynamic stiffness and equivalent viscous damping with respect to excitation frequency. The test results demonstrated that the dynamic stiffness and damping are strongly dependent on the excitation frequency. Three motion amplitudes were applied to the bearing housing to investigate the effects of motion amplitude on the dynamic characteristics. It is noted that the bearing dynamic stiffness and damping decreases with incrementally increasing motion amplitudes. A high level of misalignment can lead to larger static and dynamic bearing stiffness as well as to larger equivalent viscous damping. With dynamic loads applied to two orientations in the bearing midplane separately, the dynamic stiffness increases rapidly and the equivalent viscous damping declines slightly. These results indicate that the loading orientation is a non-negligible factor on the dynamic characteristics of MCFBs.

Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 57-63 ◽  
Author(s):  
M. J. Goodwin ◽  
P. J. Ogrodnik ◽  
M. P. Roach ◽  
Y. Fang
Keyword(s):  
Experimental Data ◽  
Dynamic Stiffness ◽  
Perturbation Technique ◽  
The Novel ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Damping Coefficients ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Novel Design

This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

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