Showing 34 results for Seismic
Kimiaei M., Shayanfar M.a., Hesham Ei Naggar M., Agha Kouchak A.a.,
Volume 2, Issue 2 (6-2004)
Abstract
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.
H. Moharrami, S.a. Alavinasab,
Volume 4, Issue 2 (6-2006)
Abstract
In this paper a general procedure for automated minimum weight design of twodimensional
steel frames under seismic loading is proposed. The proposal comprises two parts:
a) Formulation of automated design of frames under seismic loading and b) introduction of an
optimization engine and the improvement made on it for the solution of optimal design. Seismic
loading, that depends on dynamic characteristics of structure, is determined using "Equivalent
static loading" scheme. The design automation is sought via formulation of the design problem in
the form of a standard optimization problem in which the design requirements is treated as
optimization constraints.
The Optimality Criteria (OC) method has been modified/improved and used for solution of the
optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of
active set of constraints and calculation of corresponding Lagrange multipliers. The modification
has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal
design problems. Two examples have been provided to show the procedure of automated design and
optimization of seismic-resistant frames and the performance and capability of the proposed
algorithm.
F. R. Rofooei, N. K. Attari, A. Rasekh, A.h. Shodja,
Volume 4, Issue 3 (9-2006)
Abstract
Pushover analysis is a simplified nonlinear analysis technique that can be used to
estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first
steps taken in this approximate solution is to assess the maximum roof displacement, known as
target displacement, using the base shear versus roof displacement diagram. That could be done by
the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single
degree of freedom model of the original system, as well as other available approximate static
methods. In this paper, a number of load patterns, including a new approach, are considered to
construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and
tri-linear approximations of these pushover curves were used to assess the target displacements by
performing dynamic nonlinear time history analyses. The results obtained for five different special
moment resisting steel frames, using five earthquake records were compared with those resulted
from the time history analysis of the original system. It is shown that the dynamic pushover analysis
approach, specially, with the tri-linear approximation of the pushover curves, proves to have a
better accuracy in assessing the target displacements. On the other hand, when nonlinear static
procedure seems adequate, no specific preference is observed in using more complicated static
procedures (proposed by codes) compared to the simple first mode target displacement assessment.
F. Amini, R. Vahdani,
Volume 5, Issue 3 (9-2007)
Abstract
In this research, an innovative numerical simulating approach for time domain analysis
of multi degrees of freedom structures with uncertainty in dynamic properties is presented. A full
scale finite element model of multi-story and multi bays of three sample structures has been
constructed. The reduced order model of structure with holding the dominant and effective
Gramians in the balanced state-space realization has been achieved for easy and safe design of the
optimal control forces applied to the structure. Some easy selective control algorithms based on the
Optimal-Stochastic control theories such as LQG, DLQRY and modified sliding mode control has
been programmed with the simulation control sequences. Some real features of accurate control
system such as time delay and noise signals in earthquake time histories and also measurement
sensors are considered in illustrative simulation models. These models can be analyzed under either
various intensity of corresponding earthquakes or desired random excitations passed through the
suitable filters providing stochastic parameters of earthquake disturbances. This control procedure
will be shown to be very efficient suppressing all the severities and difficulties may arise in design
of a multi-objective optimal control system. The obtained results illustrate the feasibility and
applicability of the proposed stochastic optimal control design of active control force providing a
stable and energy-saving control strategy for tall building structures.
S. N. Moghaddas Tafreshi,
Volume 6, Issue 4 (12-2008)
Abstract
This paper presents the numerical analysis of seismic soil-pile-superstructure interaction in soft clay using free-field soil analysis and beam on Winkler foundation approach. This model is developed to compute the nonlinear response of single piles under seismic loads, based on one-dimensional finite element formulation. The parameters of the proposed model are calibrated by fitting the experimental data of largescale seismic soil-pile-structure tests which were conducted on shaking table in UC Berkeley. A comparative evaluation of single piles shows that the results obtained from the proposed procedure are in good agreement with the experimental results.
M.a. Goudarzi, S.r. Sabbagh-Yazdi,
Volume 7, Issue 3 (9-2009)
Abstract
The main objective of this article is evaluation of the simplified models which have been developed for
analysis and design of liquid storage tanks. The empirical formulas of these models for predicting Maximum Sloshing
Wave Height (MSWH) are obtained from Mass Spring Models (MSM). A Finite Element Modeling (FEM) tool is used
for investigating the behavior the some selected liquid storage tanks under available earthquake excitations. First, the
results of FEM tool are verified by analyzing a liquid storage tank for which theoretical solution and experimental
measurements are readily available. Then, numerical investigations are performed on three vertical, cylindrical tanks
with different ratios of Height to Radius (H/R=2.6, 1.0 and 0.3). The behaviors of the tanks are initially evaluated using
modal under some available earthquake excitations with various vibration frequency characteristics. The FEM results
of modal analysis, in terms of natural periods of sloshing and impulsive modes period, are compared with those
obtained from the simplified MSM formulas. Using the time history of utilized earthquake excitations, the results of
response-history FEM analysis (including base shear force, global overturning moment and maximum wave height)
are compared with those calculated using simplified MSM formulations. For most of the cases, the MSWH results
computed from the time history FEM analysis demonstrate good agreements with the simplified MSM. However, the
simplified MSM doesn’t always provide accurate results for conventionally constructed tanks. In some cases, up to
30%, 35% and 70% average differences between the results of FEM and corresponding MSM are calculated for the
base shear force, overturning moment and MSWH, respectively.
A. Ghanbari, M. Ahmadabadi,
Volume 8, Issue 2 (6-2010)
Abstract
Inclined retaining walls with slopes less than perpendicular are appropriate candidates in several
engineering problems. Yet, to the knowledge of authors, only a few analytical solution for calculation of active earth
pressure on such walls, which will be usually smaller than the same pressure on vertical ones, has been presented
neither in research papers nor in design codes. Considering limit equilibrium concept in current research, a new
formulation is proposed for determination of active earth pressure, angle of failure wedge and application point of
resultant force for inclined walls. Necessary parameters are extracted assuming the pseudo-static seismic coefficient
to be valid in earthquake conditions. Moreover, based on Horizontal Slices Method (HSM) a new formulation is
obtained for determining the characteristics of inclined walls in granular and or frictional cohesive soils. Findings of
present analysis are then compared with results from other available methods in similar conditions and this way, the
validity of proposed methods has been proved. Finally according to the results of this research, a simplified relation
for considering the effect of slope in reduction of active earth pressure and change in failure wedge in inclined
retaining walls has been proposed.
S.m. Mir Mohammad Hosseini, A.a. Hajimohammadi, A. R. Hajimohammadi,
Volume 8, Issue 2 (6-2010)
Abstract
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.
H. Shakib, F. Omidinasab, M.t. Ahmadi,
Volume 8, Issue 3 (9-2010)
Abstract
Elevated water tanks as one of the main lifeline elements are the structures of high importance. Since they are extremely vulnerable under lateral forces, their serviceability performance during and after strong earthquakes is a matter of concern. As such, in recent years, the seismic behavior of water tanks has been the focus of a significant amount of studies. In the present work, three reinforced concrete elevated water tanks, with a capacity of 900 cubic meters and height of 25, 32 and 39 m were subjected to an ensemble of earthquake records. The behavior of concrete material was assumed to be nonlinear. Seismic demand of the elevated water tanks for a wide range of structural characteristics was assessed. The obtained results revealed that scattering of responses in the mean minus standard deviation and mean plus standard deviation are approximately 60% to 70 %. Moreover, simultaneous effects of mass increase and stiffness decrease of tank staging led to increase in the base shear, overturning moment, displacement and hydrodynamic pressure equal to 10 - 20 %, 13 - 32 %, 10 - 15 % and 8 - 9 %, respectively.
M. Miraboutalebi, F. Askari, O. Farzaneh,
Volume 9, Issue 4 (12-2011)
Abstract
In this paper, the effect of bedrock inclination on seismic performance of slopes is investigated. The study was conducted based
on dynamic analysis of different slopes, evaluation of the earthquake acceleration in sliding mass, and calculating the
permanent displacement of the slope, using Newmark sliding block. The investigation indicates that variation of the bedrock
inclination may cause the acceleration magnitude and the displacement in the sliding mass to reach to their maximum level.
This may happen in conditions that the mean period of the acceleration time history on failure surface (Tmt) and the
predominant period of the slope (Ts ) are close to each other. Typical results are presented and discussed. A two dimensional
model of a typical slope was considered and conducting dynamic analyses, the slope performance was studied for different
geometries, strength parameters and shear wave velocities. Such a performance has been studied by assessing the record of
acceleration in sliding mass (the mass above the critical sliding surface) and calculating the slope displacement using Newmark
method. It is shown that neglecting the effect of bedrock inclination, would lead to non-real results in assessing the seismic slope
performance.
M. Davoodii, M. K. Jafari, S. M. A. Sadrolddini,
Volume 11, Issue 1 (5-2013)
Abstract
Spatial Variation of Earthquake Ground Motion (SVEGM) is clearly indicated in data recorded at dense seismographic arrays
The main purpose of this paper is to study the influence of SVEGM on the seismic response of large embankment dams. To this
end, the Masjed Soleyman embankment dam, constructed in Iran is selected as a numerical example. The spatially varying ground
motion time histories are generated using spectral representation method. According to this methodology, the generated time
histories are compatible with prescribed response spectra and reflect the wave passage and loss of coherence effects. To
investigate the sensitivity of the dam responses to the degree of incoherency, three different coherency models are used to simulate
spatially variable seismic ground motions. Finally, the seismic response of the dam under multi-support excitation is analyzed
and compared to that due to uniform ground motion. Also, the Newmark's method is used to estimate seismic-induced permanent
displacements of the embankment dam. The analysis results reveal that the dam responses can be sensitive to the assumed spatial
variation of ground motion along its base. As a general trend, it is concluded that the use of multi-support excitation, which is
more realistic assumption, results in lower acceleration and displacement responses than those due to uniform excitation.
F. Askari, M. R. Arvin, O. Farzaneh,
Volume 11, Issue 2 (11-2013)
Abstract
Seismic stability of slopes is typically evaluated by conventional methods under the assumption that the slope is subjected to an
earthquake just for one time. In general, time histories of loadings on slopes are unknown and loads are of variable repeated
nature. Shakedown phenomenon can be considered as a safe state for slopes subjected to variable repeated loadings. In this study,
lower bound dynamic shakedown theorem is employed for the seismic stability of slopes as a comprehensive verification. A
numerical method applied previously to evaluate roads under the traffic loads was modified to make it appropriate for dynamic
shakedown analysis in the present study. The numerical method is based on the combination of finite element and linear
programming methods. Critical PGA is employed as a comparative parameter to compare shakedown and pseudostatic methods.
Results show that, unlike pseudostaic method, shakedown approach is able to consider dynamic properties of load and slope.
Also, it is indicated that contrary to pseudostaic approach, shakedown solutions are different for slopes and embankments.
Shakedown and pseudostaic critical PGA versus dynamic properties of load and slope creates four distinct zones. It is shown that
the forgoing zones can be used as appropriate tools for seismic zonation of slopes based on their short term and long term safety
M. Biglari, I. Ashayeri,
Volume 11, Issue 2 (11-2013)
Abstract
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. Bastami, M. Hajihasani,
Volume 12, Issue 1 (3-2014)
Abstract
Dynamic analysis of the seismic performance of power substation equipment is time-consuming, expensive and uses responses that are sensitive to ground motion. This research proposes a method to derive input waves for dynamic analysis in place of original records from seismic events in Iran. In this study, a power transformer, current transformer, circuit breaker and disconnect switch are analyzed using fifty records from the far-field and near-field earthquake ground motions. Statistical analysis is done on the maximum acceleration and displacement responses to obtain their pushover curves. Sinusoidal waves were created using the fundamental frequencies of the equipments and PGA of 0.1g through 0.5 g as the amplitude. The results are compared with the original records and show that the proposed input waves provide a reasonable fit for an extensive range of near-field and far-field ground motion results.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)
Abstract
Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
Guray Arslan, Melih Hacisalihoglu, Muzaffer Balci, Muzaffer Borekci,
Volume 12, Issue 2 (6-2014)
Abstract
The main cause of structural damage in buildings subjected to seismic actions is lateral drift. In almost all reinforced concrete (RC) structures, whether designed with walls or frames, it is likely to be the code drift limits that control the design drift. The design drift limits and their contribution to damage may be represented indirectly through the material strain limits. The aim of this study is to investigate the seismic design indicators of RC columns using finite element analyses (FEA). The results of FEA have been compared with the results of experimental studies selected from literature. It is observed that the lateral load-deflection curves of analyzed columns are in agreement with the experimental results. Based on these lateral load-deflection curves, the drift limits and the material strain limits, given by the codes as performance indicator, are compared. It is observed that the material strain limits are non-conservative as performance indicator of RC columns, compared to the drift limits.
Mohsen Shahrouzi, Amir Abbas Rahemi,
Volume 12, Issue 2 (6-2014)
Abstract
Well-known seismic design codes have offered an alternative equivalent static procedure for practical purposes instead of verifying design trials with complicated step-y-step dynamic analyses. Such a pattern of base-shear distribution over the building height will enforce its special stiffness and strength distribution which is not necessarily best suited for seismic design. The present study, utilizes a hybrid optimization procedure to seek for the best stiffness distribution in moment-resistant building frames. Both continuous loading pattern and discrete sizing variables are treated as optimization design variables. The continuous part is sampled by Harmony Search algorithm while a variant of Ant Colony Optimization is utilized for the discrete part. Further search intensification is provided by Branch and Bound technique. In order to verify the design candidates, static, modal and time-history analyses are applied regarding the code-specific design spectra. Treating a number of building moment-frame examples, such a hyper optimization resulted in new lateral loading patterns different from that used in common code practice. It was verified that designing the moment frames due to the proposed loading pattern can result in more uniform story drifts. In addition, locations of the first failure of columns were transmitted to the upper/less-critical stories of the frame. This achievement is important to avoid progressive collapse under earthquake excitation.
S. N. Moghaddas Tafreshi, T. Nouri. A,
Volume 12, Issue 2 (4-2014)
Abstract
This paper presents a simple solution based on the limit equilibrium of sliding soil wedge of reinforced backfill subjected to
the horizontal acceleration in the framework of the pseudo-static method. In particular, contrary to most studies on the
reinforced retaining wall, the solution proposed in this study, takes into account the effect of the uniform surcharge on the
reinforced backfill soil and of its distance from the face of the wall. The results are investigated in dimensionless form of the
maximum reinforcement required strength (Kmax), the dimension of the sliding wedge (Lc/H), and the factor of safety (FS).
Compared to the reinforced backfill without surcharge, the presence of surcharge over the reinforced backfill and of its
distance from the top of the backfill have significant effects on the stability of the system. For a fixed surcharge, a minimum
distance of surcharge exists for which the presence of the surcharge does not affect the solution and the failure mechanism is
that corresponding to the case of system with no surcharge. A detailed design example is included to illustrate usage of
proposed procedures. Comparisons of the present results with available results show a favorable agreement.
H. B. Ozmen, M. Inel, S. M. Senel, A. H. Kayhan,
Volume 13, Issue 1 (3-2015)
Abstract
Seismic performance and loss assessment studies for stock of buildings are generally based on representative models due to extremely large number of vulnerable buildings. The main problem is the proper reflection of the building stock characteristics well enough by limited number of representative models. This study aims to provide statistical information of structural parameters of Turkish building stock for proper modeling using a detailed inventory study including 475 low and mid-rise RC building with 40351 columns and 3128 beams for member properties. Thirty-five different parameters of existing low and mid-rise Turkish RC building stock are investigated. An example application is given to express use of given statistical information. The outcomes of the current study and previous studies are compared. The comparison shows that the previous studies have guidance for limited number of parameters while the current study provides considerably wide variety of structural and member parameters for proper modeling.
A. Komak Panah, A.h. Khoshay,
Volume 13, Issue 2 (6-2015)
Abstract
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.