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Showing 27 results for Damping

Kimiaei M., Shayanfar M.a., Hesham Ei Naggar M., Agha Kouchak A.a.,
Volume 2, Issue 2 (6-2004)

The seismic response of pile-supported offshore structures is strongly affected by the nonlinear behavior of the supporting piles. Nonlinear response of piles is the most important source of potentially nonlinear dynamic response of offshore platforms due to earthquake excitations. It is often necessary to perform dynamic analysis of offshore platforms that accountsfor soil nonlinearity, discontinuity condition at pile soil interfaces, energy dissipation through soil radiation damping and structural non linear behaviors of piles.In this paper, an attempt is made to develop an inexpensive and practical procedure compatible with readily available structural analysis software for estimating the lateral response of flexible piles embedded in layered soil deposits subjected to seismic loading. In the proposed model a BNWF (Beam on Nonlinear Winkler Foundation) approach is used consisting of simple nonlinear springs, dash pots and contact elements. Gapping and caving-in conditions at the pile-soil interfaces are also considered using special interface elements. This model was incorporated into a Finite Element program (ANSYS), which was used to compute the response of laterally excited piles. A linear approach was used for seismic free field ground motion analysis. The computed responses compared well with the Centrifuge test results.This paper deals with the effects of free field ground motion analysis on seismic non linear behavior of embedded piles. Different parts of a BNWF (Beam on Nonlinear Winkler Foundation) model, together with quantitative and qualitative findings and conclusions for dynamic nonlinear response of offshore piles, are discussed and addressed in detail. The proposed BNWF model (only using the existing features of the available general finite element software) could easily be implemented in a more comprehensive model of nonlinear seismic response analysis of pile supported offshore platforms.
M. Khanzadi, G. Ghodrati Amiri, G. Abdollahzadeh Darzi,
Volume 5, Issue 1 (3-2007)

According to performance-based seismic design method by using energy concept, in this paper it is tried to investigate the duration and damping effects on elastic input energy due to strong ground motions. Based on reliable Iranian earthquake records in four types of soils, structures were analyzed and equivalent velocity spectra were computed by using input energy. These spectra were normalized with respect to PGA and were drawn for different durations, damping ratios and soil types and then effects of these parameters were investigated on these spectra. Finally it was concluded that in average for different soil types when the duration of ground motions increases, the input energy to structure increases too. Also it was observed that input energy to structures in soft soils is larger than that for stiff soils and with increasing the stiffness of the earthquake record soil type, the input energy decreases. But damping effect on input energy is not very considerable and input energy to structure with damping ratio about 5% has the minimum value.
A. Haddad, Gh. Shafabakhsh,
Volume 5, Issue 2 (6-2007)

Local site conditions have a strong effect on ground response during earthquakes. Two important soil parameters that control the amplification effects of seismic motions by a soil column are the soil hysteretic damping ratio and shear wave velocity. This paper presents the results of in situ damping ratio measurements performed using continuous surface wave attenuation data at a site in Semnan University campus and analysis used to obtain the near surface soils damping ratio profile. Once the frequency dependent attenuation coefficients are determined, the shear damping ratio profile is calculated using an algorithm based on constrained inversion analysis. A computer code is developed to calculate the shear damping ratio in each soil layer. Comparisons of the in situ shear damping ratio profile determined from continuous surface wave with cross hole independent test measurements are also presented. Values of shear damping ratio, obtained using continuous surface wave measurements, were less than the measured using cross hole tests, possibly because of the higher frequencies used in cross hole tests.
Shahram Feizee Masouleh, Kazem Fakharian,
Volume 6, Issue 3 (9-2008)

A finite-difference based continuum numerical model is developed for the pile-soil dynamic response during pile driving. The model is capable of simulating the wave propagation analysis along the pile shaft and through the soil media. The pile-soil media, loading and boundary conditions are such that axisymmetric assumption seems to be an optimized choice to substantially reduce the analysis time and effort. The hydrostatic effect of water is also considered on the effective stresses throughout the soil media and at the pilesoil interface. The developed model is used for signal matching analysis of a well-documented driven pile. The results showed very good agreement with field measurements. It is found that the effect of radiation damping significantly changes the pile-soil stiffness due to the hammer blow. The pile tip response shows substantial increase in soil stiffness below and around the pile tip due to driving efforts.
G. Ghodrati Amiri, F. Manouchehri Dana, S. Sedighi,
Volume 6, Issue 3 (9-2008)

By application of design spectra in seismic analyses, determination of design spectra for different site conditions, magnitudes, safety levels and damping ratios will improve the accuracy of seismic analysis results. The result of this research provides different design acceleration spectra based on Iran earthquakes database for different conditions. For this purpose first a set of 146 records was selected according to causative earthquake specifications, device error modification and site conditions. Then the design acceleration spectra are determined for 4 different site conditions presented in Iranian code of practice for seismic resistant design of buildings (Standard No. 2800), different magnitudes (MsO5.5 & Ms>5.5), different damping ratios (0, 2, 5, 10, 20 percent) and also various safety levels (50% & 84%). Also this research compares the determined design spectra with those in Standard No. 2800.
H. Shahnazari, M. Esmaeili, H. Hosseini Ranjbar,
Volume 8, Issue 2 (6-2010)

Considerations on the explosion resistant design of special infrastructures have increased in the recent

years. Amongst the various types of infrastructures, road and railway tunnels have a unique importance due to their

vital role in connection routes in emergency conditions. In this study, the explosion effects of a projectile impacting on

a railway tunnel located in a jointed rock medium has been simulated using 2D DEM code. Primarily, a GP2000

projectile has been considered as a usual projectile and its penetration depth plus its crater diameter were calculated

in rock mass. The blast pressure was, then, calculated via empirical formula and applied on the boundary of crater as

input load. Finally, the wave pressure propagation through the jointed rock medium was investigated. In part of the

study a sensitivity analysis has been carried out on jointed rock parameters such as joint orientation, dynamic modulus

and damping ratio. Their effects on tunnel lining axial force as well as bending moment have also been investigated.

S.m. Mir Mohammad Hosseini, A.a. Hajimohammadi, A. R. Hajimohammadi,
Volume 8, Issue 2 (6-2010)

Seismic piezocone device (SCPTu) together with Resonant Column and Cyclic Triaxial test apparatus are

employed to measure small strain shear modulus (G0) of carbonate sandy and clayey soils of southern coasts of Iran.

A large area of southern regions of Iran is formed from clay, silt and sand. In this study, maximum shear modulus that

is derived from both field (by seismic piezocone) and laboratory (by Resonant Column and Cyclic Triaxial) tests on

soil samples from the southern region, indicated a meaningful effect of sample disturbance. Results show that in

laboratory tests, loose samples tend to become denser and therefore exhibit greater stiffness whereas dense samples

tend to become looser, showing a reduction in stiffness. According to the results of the present study, there are narrow

limits of soils shear moduli for which the laboratory tests and the field measurements yield approximately the same

amounts. This limit of shear moduli is about 30-50(MPa) for clay deposits and 70-100 (MPa) for sandy deposits. Since

the shear moduli of soils in small strains can also be computed from the shear wave velocity, also correlations based

on parameters derived from SCPTu test for shear wave velocity determination of sandy and clayey soils of the studied

area are presented. This study shows that shear wave velocity can be related to both corrected tip resistance and total

normal stress. The measurements of the damping ratio and shear module, because of a great disturbance of stiff

deposits during the sampling process and also due to considerable differences between the laboratory and field

results, by the laboratory approaches are not reliable and advised.

A. Hassanipour, A. Shafiee, M.k. Jafari,
Volume 9, Issue 4 (12-2011)

Shear modulus and damping ratio are important input parameters in dynamic analysis. A series of resonant column tests was

carried out on pure clays and sand-clay mixtures prepared at different densities to investigate the effects of aggregate content,

confining stress, void ratio and clay plasticity on the maximum shear modulus and minimum damping ratio. Test results revealed

an increase in the maximum shear modulus of the mixture with the increase in sand content up to 60%, followed by a decrease

beyond this value. It was also found that the maximum shear modulus increases with confining stress, and decreases with void

ratio. In addition, minimum damping ratio increases with sand content and clay plasticity and decreases with confining stress.

Finally, on the basis of the test results, a mathematical model was developed for the maximum shear modulus.

R. Attarnejad, F. Kalateh,
Volume 10, Issue 1 (3-2012)

This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.

M. Biglari, I. Ashayeri,
Volume 11, Issue 2 (11-2013)

Seismic ground motion is profoundly affected by geometrical and mechanical properties of soil deposits overlaying bedrock.

Local seismic ground response of saturated soil deposits was studied in literature by applying the effects of soil stress state

and index properties on the strain-dependent normalized shear modulus reduction, G/G0, and damping ratio, D, curves in an

equivalent linear analysis. However, experimental investigations revealed that, G0, G/G0, and D of unsaturated soils are

influenced by stress state as well as suction. This study presents the results of linear and equivalent linear seismic ground response

analysis of unsaturated soil deposits incorporating suction effects on G/G0 and D curves. Seismic ground response analyses were

done with the computer program EERA for three sets of soil profiles, which are included in saturated, constant and linearly

variable suction unsaturated soil deposits. The results of current study present the magnitude of variation in natural frequency,

amplification ratio and spectral acceleration of unsaturated soil deposits.

M. Mohamamdi Ghazimahalleh, R. M. Ghazimahalleh,
Volume 11, Issue 3 (9-2013)

A new type of infilled frame has been recently proposed. It has a frictional sliding fuse, horizontally installed at the mid-height of the infill. It has already shown that such infilled frames have higher ductility, strength and damping ratio as well as more enhanced hysteresis cycles, compared with regular infilled frames. This experimental paper is focused on the influence of gravitational load on the behaviour of the fused infill panel. Furthermore, a repairing method in which damaged specimens are repaired by grout plasters is also studied. The results show that the gravitational load, applied to the surrounding frame of the infill for the dead or live loads, arises the ultimate strength of the fused infill specimens. It is also shown that repairing the failed specimen by grout was so efficient that the repaired specimen had greater strength than the original one. However, top gap, between the infill and the top beam of the enclosing frame should be absolutely avoided, because it decays the ultimate strength.
H. Zhou, L.m. Sun,
Volume 11, Issue 3 (9-2013)

Damping of a full-scale cable with a pair of passive–on magnetorheological (MR) dampers was tested. A cable of 215.58m long with the first mode frequency of 0.658Hz was tensioned horizontally in cable prefabrication factory. Two MR dampers were attached to the cable in an angle in the plane perpendicularly to the cable axis in 5m length from the cable anchorage. The applied voltage level was 0V, 3V, 6V and 9V. The cable was excited manually to a certain amplitude level for the first three modes of vertical vibration. The free decay curves of the cable were then recorded. The damping of the cable was calculated from the measured anti-node vibration amplitude. The damping of the free cable was also tested for reference. It was found that the damping of the cable is still low when MR dampers were no voltage strengthened. However, the damping of the cable increased greatly for the other with MR damper cases compared to free cable. Further study showed that the damping of the cable with MR dampers were strongly depended on applied voltage level and vibration amplitude. There is an optimal damping value when MR damper is voltage strengthened. The dependence of the optimum damping on applied voltage level, vibration amplitude and vibration mode was further analyzed.
H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)

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.
M. Abbasi, A. H. Davaei Markazi,
Volume 12, Issue 1 (3-2014)

An important factor in the design and implementation of structural control strategies is the number and placement of actuators. By employing optimally-located actuators, the effectiveness of control system increases, while with an optimal number of actuators, an acceptable level of performance can be achieved with fewer actuators. The method proposed in this paper, simultaneously determines the number and location of actuators, installed in a building, in an optimal sense. In particular, a genetic algorithm which minimizes a suitably defined structural damage index is introduced and applied to a well-known nonlinear model of a 20-story benchmark building. It is shown in the paper that an equal damage protection, compared to the work of other researchers, can be achieved with fewer numbers of optimally placed actuators. This result can be important from economic point of view. However, the attempt to minimize one performance index has negative effect on the others. To cope with this problem to some extent, the proposed genetic methodology has been modified to be applied in a multi-objective optimization problem.
R. Vidjeapriya, V. Vasanthalakshmi, K. P. Jaya,
Volume 12, Issue 1 (3-2014)

The present study focuses on the performance of precast concrete beam-column dowel connections subjected to cyclic loading by conducting experiments. In this study, one-third scale model of two types of precast and a monolithic beam-column connection were cast and tested under reverse cyclic loading. The precast connections considered for this study is a beam-column connection where beam is connected to column with corbel using (i) dowel bar and (ii) dowel bar with cleat angle. The experimental results of the precast specimens have been compared with that of the reference monolithic connection. The sub-assemblage specimens have been subjected to reverse cyclic displacement-controlled lateral loading applied at the end of the beam. The performance of the precast connections in terms of the ultimate load carrying capacity, post- elastic strength enhancement factor, load-displacement hysteresis behaviour, moment-rotation hysteresis behaviour, energy dissipation capacity, equivalent viscous damping ratio and ductility factor were compared with that of the monolithic beam-column connection. The monolithic specimen was found to perform better when compared to the precast specimens in terms of strength and energy dissipation. In terms of ductility, the precast specimen using dowel bar and cleat angle showed better behaviour when compared to the reference monolithic specimen.
M. Afzalirad, M. Kamalian, M. K. Jafari, A. Sohrabi-Bidar,
Volume 12, Issue 1 (1-2014)

In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
A. Kaveh, M.s. Massoudi ,
Volume 12, Issue 2 (6-2014)

Formation of a suitable null basis is the main problem of finite elements analysis via force method. For an optimal analysis, the selected null basis matrices should be sparse and banded corresponding to sparse, banded and well-conditioned flexibility matrices. In this paper, an efficient method is developed for the formation of the null bases of finite element models (FEMs) consisting of tetrahedron elements, corresponding to highly sparse and banded flexibility matrices. This is achieved by associating special graphs with the FEM and selecting appropriate subgraphs and forming the self-equilibrating systems (SESs) on these subgraphs. Two examples are presented to illustrate the simplicity and effectiveness of the presented graph-algebraic method.
L. Kalani Sarokolayi, B. Navayi Neya, Javad Vaseghi Amiri,
Volume 13, Issue 1 (3-2015)

This study focuses on non-linear seismic response of a concrete gravity dam subjected to translational and rotational correlated components of ground motions including dam-reservoir interaction. For this purpose rotational components of ground motion is generated using Hong Non Lee improved method based on corresponding available translational components. The 2D seismic behavior of the dam concrete is taken into account using nonlinear fracture mechanics based on the smeared- crack concepts and the dam-reservoir system are modeled using Lagrangian-Lagrangian approach in finite element method. Based on presented formulation, Pine Flat concrete gravity dam is analyzed for different cases and results show that the rotational component of ground motion can increase or decrease the maximum horizontal and vertical displacements of dam crest. These results are dependent on the frequency of dam-reservoir system and predominant frequencies of translational and rotational components of ground motion.
A. Komak Panah, A.h. Khoshay,
Volume 13, Issue 2 (6-2015)

To increase the safety of structures against strong ground motions and their life due to environmental issues on the earth and saving in terms of materials, it is necessary to expand and upgrade seismic resistant systems. However, more cost-effective systems which have sufficient influence on the seismic performance of structures and also more compatibility with the regional conditions, will be more desirable than other systems. One of the seismic resistance systems is seismic isolation. In the event of interest in using the seismic isolation system for a mounted building on piles, the costly construction of piles and isolation equipment shall be provided simultaneously. The seismic isolating using sleeved-piles which is generally used in combination with various damper systems, can help to overcome this issue. In this research a seismic isolator system using sleeved-pile has been studied while considering the damping behavior of the soil-rubber mixture as the only source of damping. To investigate the proposed system, a series of tests including static lateral load test, dynamic free and forced vibration tests, were performed on a model pile in a field laboratory which has been constructed for this purpose. According to results of tests the proposed system has a good deformation ability and damping characteristics, and as a method of seismic isolation is completely efficient.

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