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.

A numerical study on the influences of underlying soil and backfill characteristics on the dynamic behaviour of typical integral bridges

Bauingenieur ◽  
2020 ◽  
Vol 95 (11) ◽  
pp. S 2-S 11
Author(s):  
H. D. B. Aji ◽  
M. B. Basnet ◽  
Frank Wuttke
Keyword(s):  
Soil Structure ◽  
Dynamic Behaviour ◽  
Numerical Study ◽  
Coupled System ◽  
Soil Structure Interaction ◽  
Dynamic Resistance ◽  
Soil Characteristic ◽  
Structure Interaction ◽  
Integral Bridges ◽  
Underlying Soil

Abstract The identification of the dynamic behaviour of a structure is one of the crucial steps in the design of the dynamic resistance of the structure. The dynamic behaviour is represented by the natural frequencies and damping which are subsequently used along with the considered dynamic actions in the design process. In regard of integral bridge concept, one of the consequences of the omission of joints and bearings is the substantial soil-structure interaction which in turn increases the sensitivity of the dynamic behaviour of the bridges to the surrounding soil characteristic. In this article, we extended our hybrid BEM-FEM steady-state dynamic numerical tool to the 3D regime, developed by utilizing an in-house BEM and the commercial FEM software ABAQUS and use it to analyse the dynamic interaction between the bridge and the underlying soil as well as the backfill. The numerical results from four typical integral bridges show that underlying soil characteristic has great effect on the resonant frequencies and the damping. The backfill material properties tend to have less significant role due to the abutment wingwalls dominating the force transfer between the soil and the superstructure. The results also show that the degree of influence of the soil-structure interaction on the coupled system is affected by the type of load pattern in addition to the flexural stiffness of the superstructure.

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.

Seismic response of sands in centrifuge tests

2008 ◽  
Vol 45 (4) ◽  
pp. 470-483 ◽  
Author(s):  
Mohammad H.T. Rayhani ◽  
M. Hesham El Naggar
Keyword(s):  
Shear Modulus ◽  
Seismic Response ◽  
Soil Structure ◽  
Site Response ◽  
Damping Ratio ◽  
Soil Structure Interaction ◽  
Response Analysis ◽  
Structure Interaction ◽  
Centrifuge Tests ◽  
Seismic Site Response

Seismic site response of sandy soils and seismic soil–structure interaction are investigated using an electrohydraulic earthquake simulator mounted on a centrifuge container at an 80g field. The results of testing uniform and layered loose to medium-dense sand models subjected to 13 simulated earthquakes on the centrifuge are presented. The variation of shear modulus and damping ratio with shear strain amplitude and confining pressure was evaluated and their effects on site response were assessed. The evaluated shear modulus and damping ratio agreed reasonably with laboratory tests and empirical relationships. Site response analysis using the measured shear wave velocity and estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured site response. The effect of soil–structure interaction for structures situated on dry sand is also investigated. These tests have revealed many important insights with regard to the characteristics of seismic site response and seismic soil–structure behaviour. The tests showed that the seismic response of soil deposits, input motions, and overall behaviour of the structure are affected by soil stratification. The results showed that the seismic kinematic soil–structure interaction is not very significant for structures situated on loose sand.

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.

Study of Responses of 64-Story Rincon Building to Napa, Fremont, Piedmont, San Ramon Earthquakes and Ambient Motions

2017 ◽  
Vol 33 (3) ◽  
pp. 1125-1148 ◽  
Author(s):  
Mehmet Çelebi ◽  
John Hooper ◽  
Ron Klemencic
Keyword(s):  
San Francisco ◽  
Soil Structure ◽  
Nonlinear Behavior ◽  
Shear Wall ◽  
Soil Structure Interaction ◽  
Concrete Core ◽  
Structure Interaction ◽  
Fundamental Frequencies ◽  
Ambient Data ◽  
Liquid Dampers

We analyze the recorded responses of a 64-story, instrumented, concrete core shear wall building in San Francisco, California, equipped with tuned sloshing liquid dampers (TSDs) and buckling restraining braces (BRBs). Previously, only ambient data from the 72-channel array in the building were studied ( Çelebi et al. 2013 ). Recently, the 24 August 2014 Mw 6.0 Napa and three other earthquakes were recorded. The peak accelerations of ambient and the larger Napa earthquake responses at the basement are 0.12 cm/s/s and 5.2 cm/s/s respectively—a factor of ∼42. At the 61st level, they are 0.30 cm/s/s (ambient) and 16.8 cm/s/s (Napa), respectively—a factor of ∼56. Fundamental frequencies (NS ∼ 0.3, EW ∼ 0.27 Hz) from earthquake responses vary within an insignificant frequency band of ∼0.02–0.03 Hz when compared to those from ambient data. In the absence of soil-structure interaction (SSI), these small and insignificant differences may be attributed to (1) identification errors, (2) any nonlinear behavior, and (3) shaking levels that are not large enough to activate the BRBs and TSDs to make significant shifts in frequencies and increase damping.

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.

Sign in / Sign up

Export Citation Format

Share Document