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Showing 9 results for Soil-Structure Interaction

M.h. Baziar, A. Ghorbani, R. Katzenbach,
Volume 7, Issue 3 (9-2009)
Abstract

The pile-raft foundation is a combination of a raft foundation with piles. Pile-raft foundation has been widely designed, assuming all structure loads to be transferred to piles without considering contribution of the load taken by contact surface between raft and soil. Methods of analysis currently used in practice are based upon relatively conservative assumptions of soil behavior or on the less realistic soil-structure interaction. In this study the bearing -settlement behavior of combined pile-raft foundations on medium dense sand was investigated. 1g physical model test was performed on a circular rigid raft underpinned with four model piles. Numerical simulation was also carried out on the model test, using FLAC-3D, to show compatibility of the numerical analysis with the test. The obtained results showed very good accuracy of the numerical method used in this study as long as the applied load does not exceed the working load, while the performance of numerical model was relatively good for the loads beyond working load.
A. Ghanbari, E. Hoomaan, M. Mojallal,
Volume 11, Issue 1 (5-2013)
Abstract

For calculating the natural frequency of structures such as buildings, chimneys, bridges and silos appropriate analytical

formulas exist. However, in the case of retaining walls undergoing the soil pressure at one side, calculating the natural frequency

is not a straightforward task and requires the effects of soil-structure interactions to be considered. By modeling the soil as series

of linear springs, a new formulation is presented in this article, to calculate the natural frequency of retaining walls. This formula

considers the vertical cross sectional width change, and hence, enables us to calculating the natural frequency of retaining walls

with different types of backfill. The geometrical properties of the retaining walls and its bending rigidity together with the soil’s

modulus of elasticity and its Poisson’s ratio are the most important parameters to calculate. A comparison of the results for

retaining walls with constant cross section obtained from the suggested method with those of the software analyses was carried

out and good agreement was detected. A second comparison of the results with those of other researchers revealed that the natural

frequency of flexible retaining wall is an upper bound for natural frequency of rigid walls. The Selected shape function is also

very close to the real shape mode.


H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)
Abstract

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
Amir Hossein Jafarieh, Mohammad Ali Ghannad,
Volume 12, Issue 2 (6-2014)
Abstract

It is well-known that the behavior of soil-structure systems can be well described using a limited number of non-dimensional parameters. This is the outcome of researches based on the premise that the foundation is bonded to the ground. Here, it is shown the concept can be extended to systems with foundation uplift. A set of non-dimensional parameters are introduced which controls the main features of uplifting systems. The effect of foundation uplift on response of soil-structure systems are investigated parametrically through time history analysis for a wide range of systems subjected to ground motions recorded on different soil types. In particular, the effects of uplift on displacement ratio, defined as the ratio of maximum displacement of the uplifting system to that of the elastic system without uplifting and drift ratio, defined as the ratio of maximum drift of the structure as a part of uplifting soil-structure system to that of the elastic system without uplifting, are investigated. It is observed that in general foundation uplift reduces the drift response of structures, which in turn, results in lower base shear. The reduction reaches about 35 percent for slender structures located on relatively soft soils subjected to strong ground motions. Simplified expressions are suggested to estimate this reduction in the base shear.
M.a. Rahgozar,
Volume 13, Issue 3 (12-2015)
Abstract

The interactive effects of adjacent buildings on their seismic performance are not frequently considered in seismic design. The adjacent buildings, however, are interrelated through the soil during seismic ground motions. The seismic energy is redistributed in the neighboring buildings through multiple structure-soil-structure interactions (SSSI). For example, in an area congested with many nearby tall and/or heavy buildings, accounting for the proximity effects of the adjacent buildings is very important. To solve the problem of SSSI successfully, researchers indicate two main research areas where need the most attention: 1) accounting for soil nonlinearity in an efficient way, and 2) spatial analysis of full 3D soil-structure models. In the present study, three-dimensional finite element models of tall buildings on different flexible foundation soils are used to evaluate the extent of cross interaction of adjacent buildings. Soil nonlinearity under cyclic loading is accounted for by Equivalent Linear Method (ELM) as to conduct large parametric studies in the field of seismic soil-structure interaction, the application of ELM is preferred over other alternatives (such as application of complicated constitutive soil models) due to the efficiency and reliability of its results. 15 and 30 story steel structures with pile foundations on two sandy and clayey sites are designed according to modern codes and then subjected to several actual earthquake records scaled to represent the seismicity of the building sites. Results show the cross interaction of adjacent buildings on flexible soils, depending on their proximity, increases dynamic displacements of buildings and reduces their base shears. 


M. Davoodi, M. Sadjadi,
Volume 13, Issue 3 (12-2015)
Abstract

The distinctive characteristics of near-field earthquake records can lead to different structural responses from those experienced in far-field ones. Furthermore, soil-structure interaction (SSI) can have a crucial influence on the seismic response of structures founded on soft soils however, in most of the time has been neglected nonchalantly. This paper addresses the effects of near-field versus far-field earthquakes on the seismic response of single degree of freedom (SDOF) system with considering SSI. A total 71 records were selected in which near-field ground motions have been classified into two categories: first, records with a strong velocity pulse, (i.e. forward-directivity) second, records with a residual ground displacement (i.e. fling-step). Findings from the study reveal that pulse-type near-field records generally produce greater seismic responses than far-field motions especially at high structure-to-soil stiffness ratios. Moreover, the importance of considering SSI effects in design of structures is investigated through an example. Finally, parametric study between Peak Ground Velocity to Peak Ground Acceleration ratio (PGV/PGA) of pulse-like ground motions and maximum relative displacement indicate that with increase in structure-to-soil stiffness ratios, earthquakes with higher PGV/PGA ratio produce greater responses.


Dongdong Zhang,
Volume 14, Issue 8 (12-2016)
Abstract

This paper compares the seismic load of a 5MW wind turbine supported by a 100-m-high prestressed concrete tower calculated via time history analysis and response spectrum analysis using elastic acceleration spectrum provided by the China Aseismic Code for Buildings. With 5% damping ratio, the fixed-based Multi-degree of freedom model and Finite element model considering soil structure interaction are used for response spectrum analysis and time history analysis, respectively. The results indicated that the seismic load calculated by response spectrum analysis is significantly larger than the results associated with the time history analysis method. It implies that the seismic load determined from common building code procedures along with other loads for wind turbine foundation design is too conservative. Within this paper, the effects of damping ratio, horizontal acceleration amplitude, spring stiffness and damping coefficient of foundation on the seismic load of the prestressed concrete wind turbine tower are discussed. It is shown that the seismic load with mode damping ratio for the prestressed concrete wind turbine tower is not significant when compared with traditional tubular steel designs. The maximum moment demand at the base of the tower may be controlled by earthquake loading as the seismic fortification intensity lever is more than seven. The foundation spring stiffness has a immensely impact on the base bending moment and the natural frequency. Finally, seismic load should be considered in more detail when designing wind turbines that are supported by concrete towers, particularly for turbine’s over 100-m tall and located in seismically active zones.


Alireza Darvishpour, Ali Ghanbari, Seyyed Ali Asghar Hosseini, Masoud Nekooei,
Volume 15, Issue 3 (5-2017)
Abstract

Most of the proposed methods for obtaining the free vibration natural frequency of the retaining wall have been presented, assuming the behavior of the wall in two-dimensional domain, and they are not able to express the three-dimensional behavior of these structures in a satisfying manner. In this paper, the plate theory is employed to analyze the free vibration of wall-soil system in three-dimensional domain. So the retaining wall is modeled as a clamped-free plate and the stiffness of the soil existing behind the wall is modeled as a set of springs. Using the approximate Rayleigh method, new analytical expression for obtaining the free vibration natural frequencies for the three first modes of the wall is represented. The results of the proposed model are compared with both the results of the other researchers and the ones from finite element method (FEM). They are also compared with the results of a full-scale experiment and it shows a good agreement. The comparison shows that modeling the wall in two-dimensional form is not accurate enough to calculate all the natural frequencies of the wall. The results of this paper show that there is a considerable difference between two- and three-dimensional behavior of the walls. The proposed method also gives the free vibration natural frequencies of the wall extensional modes with an acceptable accuracy. Finally, the effect of tensile and compressive behavior of the soil on the fundamental frequency is studied. This research can be considered as a new field in three-dimensional calculation of the retaining walls.


Farshad Homaei, Hamzeh Shakib, Masoud Soltani,
Volume 15, Issue 4 (6-2017)
Abstract

In this paper, the probabilistic seismic performance of vertically irregular steel buildings, considering soil-structure interaction effects, is evaluated. Various irregular distributions of structural properties, including mass, stiffness and strength along the height of three-dimensional moment resisting steel frames were intended. The finite element model of soil medium was created with solid elements below the structure. The nonlinear material behavior of soil was considered as well. Nonlinear incremental dynamic analysis was performed to evaluate the flexible-base structural performance in the framework of probabilistic performance-based earthquake engineering. According to the median curves of intensity-demand of structures, it is concluded that non-uniform height-wise distribution of lateral resistance properties of steel structures varies the displacement demand and the seismic capacity of the irregular frames, compare to the regular structure. The capacity variation of most irregular frames is more obvious at the nonlinear phase of structural behavior. Due to the foundation flexibility, the damage concentration raises in the bottom floor and the irregularity increase the seismic demands of the lower floors of the system. Among all the irregular steel frames, the average increase of the displacement demand and reduction of the seismic capacity are maximal for the strength and concurrent variation of stiffness and strength irregularity models, respectively. Additionally, mass irregularity shows minor influence in the seismic demand and capacity variations of the steel frames. The predominant influence of stiffness and strength irregularities (soft and weak story) is observed in reduction of the structural ductility factor and the mean annual frequency of exceeding limit states.



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