Bounds for natural frequencies, Dunkerley's formula and application to soil–structure interaction

2013 ◽  
Vol 47 ◽  
pp. 32-37 ◽  
Author(s):  
J. Enrique Luco
Keyword(s):  
Soil Structure ◽  
Natural Frequencies ◽  
Soil Structure Interaction ◽  
Structure Interaction

Seismic Response Analysis of Liaocheng Guangyue Tower

2015 ◽  
Vol 744-746 ◽  
pp. 911-914
Author(s):  
Zhao Bo Meng ◽  
Guan Dong Qiao ◽  
Jie Jin
Keyword(s):  
Seismic Response ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Timber Structure ◽  
Soil Structure Interaction ◽  
Response Analysis ◽  
Actual Situation ◽  
Seismic Response Analysis ◽  
Structure Interaction ◽  
Rare Earthquake

This paper establishes three models using ANSYS, which were timber structure of Guangyue Tower, timber structure-tower base and timber structure-tower base-foundation. The first 3 natural frequencies of timber structure respectively were 0.8524Hz、1.1273 Hz and 1.7426 Hz through modal analysis, which were compared with calculations from code. Lanzhou Wave was chosen to analyze the seismic response of Guangyue Tower, and the amplitudes were adjusted to 55gal and 310gal respectively according to the frequent earthquake and rare earthquake, which were inputted to the above models. As can be seen from the calculations, the maximum displacements of the three models were in the top nodes, and tower base had a greater impact on vibration of timber structure, which could not be ignored in seismic response analysis; considering soil-structure interaction in seismic response analysis could better reflect the actual situation of Guangyue Tower.

scholarly journals Effects of Soil-Structure Interaction on Torsionally Coupled Base Isolated Machine Foundation under Earthquake Load

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Karmegam Rajkumar ◽  
Ramanathan Ayothiraman ◽  
Vasant A. Matsagar
Keyword(s):  
Soil Structure ◽  
Natural Frequencies ◽  
Ground Motions ◽  
Soft Soil ◽  
Soil Structure Interaction ◽  
Structure Interaction ◽  
Machine Foundation ◽  
Earthquake Ground Motions ◽  
Torsional Coupling ◽  
Base Isolators

In this paper, the influence of soil-structure interaction (SSI) on a torsionally coupled turbo-generator (TG) machine foundation is studied under earthquake ground motions. The beneficial effects of base isolators in the TG foundation under earthquake ground motions are also studied duly, considering the effects of SSI. A typical TG foundation is analyzed using a three-dimensional finite element (FE) model. Two superstructure eccentricity ratios are considered to represent the torsional coupling. Soft soil properties are considered to study the effects of SSI. This research concludes that the effects of torsional coupling alter the natural frequencies, if ignored, could lead to unsafe design. The deck accelerations and displacements are increased with an increase in superstructure eccentricity. On the other hand, the deck accelerations and displacements are greatly reduced with the help of base isolators, thus confirming the beneficial use of base isolators in machine foundations to protect the sensitive equipment from the strong earthquake ground motions. However, the effects of SSI reduce the natural frequencies of the TG foundation resting on soft soil conditions and activate the higher mode participation, resulting in amplifying the response.

Buckling and Free Vibration of a Single Pile Considering the Effect of Soil–Structure Interaction

2018 ◽  
Vol 18 (04) ◽  
pp. 1850061 ◽  
Author(s):  
Jianjun Ma ◽  
Fengjun Liu ◽  
Xiaojuan Gao ◽  
Mengqiang Nie
Keyword(s):  
Critical Load ◽  
Elastic Foundation ◽  
Axial Load ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Soil Structure Interaction ◽  
Single Pile ◽  
Structure Interaction ◽  
Post Buckling ◽  
Foundation Parameter

The buckling response and free vibration characteristics of a single pile in the elastic foundation are investigated. Considering the effect of soil–structure interaction and geometric nonlinearity, the nonlinear equation of motion for a single pile is derived by Hamilton’s principle. Then, closed-form solutions of the critical load and buckled configuration of the pile are obtained analytically, and the natural frequencies of the pre- and post-buckling pile are examined. Finally, the effect of elastic foundation parameter on the critical load of the pile is discussed, and the effect of axial load on the natural frequencies of the pile is also explored. Numerical results show that the effect of elastic foundation parameter plays a dominant role on the critical load and buckled configuration of the pile, and the shear parameter affects the critical load directly. The axial load effect on the dynamic characteristics of the pre-buckling pile is significant, meanwhile, it may contribute very small to the post-buckling pile when the axial load exceeds some specific values.

Free Vibration Characteristics of Structures With Nonlinear Underlying Soil

1991 ◽  
Vol 113 (1) ◽  
pp. 95-99
Author(s):  
Kamal A. F. Moustafa ◽  
M. El-Gebeily
Keyword(s):  
Perturbation Theory ◽  
Shear Modulus ◽  
Free Vibration ◽  
Nonlinear Model ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Nonlinear Behavior ◽  
Soil Structure Interaction ◽  
Structure Interaction ◽  
Underlying Soil

Free vibration of structures is investigated by using a multidegree of freedom nonlinear model that allows for nonlinear behavior of the soil underlying the structure. The considered nonlinearity is due to the dependence of the soil shear modulus on vibration levels. The soil-structure interaction is modelled as nonlinear complex stiffness. The analysis is carried out by using mathematical perturbation theory. Modifications in the natural frequencies and existence of harmonics are demonstrated. The results are applied to an application example of massive deep water gravity structure.

scholarly journals Evaluation of Seismic Response Trends from Long-Term Monitoring of Two Instrumented RC Buildings Including Soil-Structure Interaction

2012 ◽  
Vol 2012 ◽  
pp. 1-18 ◽  
Author(s):  
Faheem Butt ◽  
Piotr Omenzetter
Keyword(s):  
Reinforced Concrete ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Free Field ◽  
Soil Structure Interaction ◽  
Rc Frame ◽  
Building Structures ◽  
Structure Interaction ◽  
Frame Building ◽  
Rc Frame Building

This paper presents analyses of the seismic responses of two reinforced concrete buildings monitored for a period of more than two years. One of the structures was a three-storey reinforced concrete (RC) frame building with a shear core, while the other was a three-storey RC frame building without a core. Both buildings are part of the same large complex but are seismically separated from the rest of it. Statistical analysis of the relationships between maximum free field accelerations and responses at different points on the buildings was conducted and demonstrated strong correlation between those. System identification studies using recorded accelerations were undertaken and revealed that natural frequencies and damping ratios of the building structures vary during different earthquake excitations. This variation was statistically examined and relationships between identified natural frequencies and damping ratios, and the peak response acceleration at the roof level were developed. A general trend of decreasing modal frequencies and increasing damping ratios was observed with increased level of shaking and response. Moreover, the influence of soil structure interaction (SSI) on the modal characteristics was evaluated. SSI effects decreased the modal frequencies and increased some of the damping ratios.

Changes of Natural Frequencies of Industrial Steel Hall due to Simplifications of Numerical Model

2013 ◽  
Vol 790 ◽  
pp. 16-20
Author(s):  
Joanna M. Dulinska ◽  
Pawel Boron
Keyword(s):  
Numerical Model ◽  
Dynamic Characteristics ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Soil Structure Interaction ◽  
Flexible Joints ◽  
Structure Interaction ◽  
Continuous Beams ◽  
Different Types ◽  
Main Frame

The paper presents changes of natural frequencies of industrial steel hall due to simplifications or changes of numerical model. Firstly, the natural frequencies were calculated for basic Variant A of the numerical model of the steel hall which consisted of the main frames, footings, roof purlins and girts. In this Variant columns were fixed at bases, both purlins and girts were rigidly connected to main frames and designed as continuous beams. Then, in Variant B of the model columns were pinned at bases. Next, in Variant C different types of connections (semi-flexible joints) of roof purlins and girts with the main frame were implemented. Finally, in Variant D, soil-structure interaction was taken into consideration. The calculations of the dynamic characteristics of four abovementioned Variants of the numerical model of the hall showed that simplifications or changes of some details of the structure could result in significant errors in values of natural frequencies.

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