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Showing 16 results for Earthquake

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.
B. Behnam, M.h. Sebt, H.m. Vosoughifar,
Volume 4, Issue 2 (6-2006)
Abstract

By identifying the damage index of a structure, in addition to a correct understanding from real behavior of the structure, the required criterion for strengthening would be given. Researchers have given many relations for determination of damage index but such relations have been based upon laboratory methods which challenge their usage in a broad term. In this paper two new methods are given for calculation of damage index. Surveying the first crack limit and total structure failure is based upon the formation of plastic joints in the first column and basic floor columns. To give a qualitative simple and functional damage index, the functional method was given in the form of a qualitative method with statistical analysis and collection of different views. Using this method is very simple and meantime offers suitable accuracy. With a numerical study on three models it was made clear that the difference of new method with amended method of Papadopolos in approximate 3%. This shows that given qualitative method is suitable to be used in a broad terms.
M. Mazloom, A.a. Mehrabian,
Volume 4, Issue 4 (12-2006)
Abstract

The objective of this paper is to present a new method for protecting the lives of residents in catastrophic earthquake failures of unreinforced masonry buildings by introducing some safe rooms within the buildings. The main idea is that occupants can seek refuge within the safe rooms as soon as the earthquake ground motions are felt. The information obtained from the historical ground motions happened in seismic zones around the globe expresses the lack of enough safety of masonry buildings against earthquake. For this potentially important reason, an attempt has been made to create some cost-effective seismic-resistant areas in some parts of the existing masonry buildings, which are called safe rooms. The practical method for creating these areas and increasing the occupant safety of the buildings is to install some prefabricated steel frames in some of their rooms or in their halls. These frames do not carry any service loads before earthquake. However, if a near field seismic event happens and the load bearing walls of the building destroy, some parts of its floors, which are in the safe areas, will fall on the roof of the installed frames consequently, the occupants who have sheltered in the safe rooms will survive. This paper expresses the experimental and theoretical work executed on the steel structures of the safe rooms for bearing the shock and impact loads. Finally, it was concluded that both the strength and displacement capacity of the steel frames were adequate to accommodate the distortions generated by seismic loads and aftershocks properly.
S. Eshghi, V. Zanjanizadeh,
Volume 5, Issue 3 (9-2007)
Abstract

This paper presents an experimental study on seismic repair of damaged square reinforced concrete columns with poor lap splices, 90-degree hooks and widely spaced transverse bars in plastic hinge regions according to ACI detailing (pre.1971) and (318-02) using GFRP wraps. Three specimens were tested in “as built” condition and retested after they were repaired by glass fiberreinforced plastic sheets. They were tested under numerous reversed lateral cyclic loading with a constant axial load ratio. FRP composite wraps were used for repairing of concrete columns in critically stressed areas near the column footings. Physical and mechanical properties of composite wraps are described. Seismic performance and ductility of the repaired columns in terms of the hysteretic response are evaluated and compared with those of the original columns. The results indicated that GFRP wraps can be an effective repair measure for poorly confined R/C columns due to short splice length and widely spaced ties with 90-degree anchorage hooks. Both flexural strength and ductility of repaired columns were improved by increasing the existing confinement in critical regions of them.
E. Kermani, Y. Jafarian, M. H. Baziar,
Volume 7, Issue 4 (12-2009)
Abstract

Although there is enough knowledge indicating on the influence of frequency content of input motion on the deformation demand of structures, state-of-the-practice seismic studies use the intensity measures such as peak ground acceleration (PGA) which are not frequency dependent. The v max/a max ratio of strong ground motions can be used in seismic hazard studies as the representative of frequency content of the motions. This ratio can be indirectly estimated by the attenuation models of PGA and PGV which are functions of earthquake magnitude, source to site distance, faulting mechanism, and local site conditions. This paper presents new predictive equations for v max/a max ratio based on genetic programming (GP) approach. The predictive equations are established using a reliable database released by Pacific Earthquake Engineering Research Center (PEER) for three types of faulting mechanisms including strikeslip, normal and reverse. The proposed models provide reasonable accuracy to estimate the frequency content of site ground motions in practical projects. The results of parametric study demonstrate that v max/a max increases through increasing earthquake moment magnitude and source to site distance while it decreases with increasing the average shear-wave velocity over the top 30m of the site.
M. Mazloom, A.a. Mehrabian,
Volume 7, Issue 4 (12-2009)
Abstract

Pullback test has no scrupulous theoretical establishment. It is based on the hypothesis that the response of

the structure can be related to the response of an equivalent single degree-of-freedom (SDOF) system. This implies that

the response is controlled by a single mode. In fact, the steel frame of each safe room, which is introduced within the

unreinforced masonry buildings for protecting the lives of residents in catastrophic earthquake failures, contains a

SDOF structural system. In pullback test, the steel frame carries its gravity load first, and then it will be pushed under

an incremental lateral roof displacement pattern, which is imposed to its center of mass. This paper expresses the

results of 13 pullback tests executed by the authors on the steel frames of safe rooms. The results show that pullback

test is a practical method for seismic performance evaluation of safe rooms. Also the performance of these frames

located in a collapsing three storey masonry building is presented with favorable conclusions. In fact, the results of

pullback test of the safe room located at the ground-floor level were compared with the requirements of Iranian code

for seismic resistant design and it was concluded that the steel frame had an acceptable performance against seismic

effects.


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.


Kabir Sadeghi,
Volume 9, Issue 3 (9-2011)
Abstract

An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structurechr('39')s force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.


A. H. Molavi-Tabrizi, F. Khoshnoudian,
Volume 10, Issue 3 (9-2012)
Abstract

The application of fuzzy algorithms in the response control of a base isolated building with MR dampers is investigated in this

paper. Most of the previous researches in this field have been focused on fuzzy algorithms with linear membership function

however in the current study the membership functions are assumed to be Gaussian and their effectiveness is studied. For this

purpose, an eight-story building with regularity in plan and height is considered. The adopted base isolation system includes

linear bearings and control devices for improving the behavior of isolated structure under near field ground motions. MR

dampers are used to reduce base displacements and have the capacity of 1000 kN with the maximum applied voltage of 10 V. In

order to verify the control procedure and analyzing the structure, a simulation procedure is developed. This procedure performs

linear analysis of the structure in presence or in absence of the base isolation system. Moreover, the simulation procedure is able

to appropriately determine the MR damper voltage using fuzzy logic algorithms and then analyzing the whole system too. Finally,

seven near-field earthquake records are chosen in order to study the structure responses under these records and the obtained

results demonstrate the accuracy of proposed control procedure


F. Khoshnoudian, O. Nozadi,
Volume 11, Issue 2 (6-2013)
Abstract

It has been pointed out the static lateral response procedure for a base-isolated structure proposed in International Building Code (IBC) somewhat overestimates the seismic story force. That is why in the current paper, vertical distribution of base shear over the height of isolated structures considering higher mode effects under near field earthquakes is investigated. Nonlinear behavior of isolation systems cause variation of frequencies transmitted to the superstructure and consequently higher modes effects should be considered. In this study base shear distribution obtained from nonlinear dynamic analysis is compared with that achieved from IBC for assessment of the international building code. This investigation has been conducted in two parts, in order to have an appropriate base shear distribution formula for isolated structures under near field earthquakes. In the first part using three first mode shapes of isolated structure and introducing coefficient corresponding to each mode, extracted from nonlinear dynamic analysis under near field earthquakes, a new formula has been derived. In the second part, the mode shape coefficients have been obtained theoretically and consequently a new base shear distribution over the height of isolated structures including the isolation system properties under near field ground motions was proposed.
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


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.
E. Wahyuni, Y. Tethool,
Volume 13, Issue 2 (6-2015)
Abstract

The purpose of this study is to determine the effect of vierendeel panel width and vertical truss spacing ratio in an inelastic behavior of the STF system due to earthquake loads. The STF system is applied to a six-storey building that serves as apartments [2]. The STF system is used in the building in the transverse direction (N-S direction), while in the longitudinal direction (W-E direction) the building system uses the special moment resisting frame. The structural behavior was evaluated using nonlinear pushover and time history analyses. The results showed that by increasing the ratio of vierendeel panel width and vertical truss spacing, the ductility of the structure was increased. Based on the performance evaluation, the ratio of the vierendeel panel width and vertical truss spacing on the STF buildings that provided satisfactory performance was more or equal to 1.6. The ultimate drift obtained from non-linear time history analysis was smaller than the pushover analysis. This result showed that the static nonlinear pushover analysis was quite conservative in predicting the behavior of the six-storey building in an inelastic condition.
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.


Hamed Tajammolian, Faramarz Khoshnoudian, Nasim Partovi Mehr,
Volume 14, Issue 8 (12-2016)
Abstract

This study is devoted to investigate the effects of mass eccentricity in seismic responses of base-isolated structures subjected to near field ground motions. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructure mounted on nonlinear isolators are subjected to 3 components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main system parameters are studied. These parameters are selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities has not a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity raise the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric superstructure. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on base shear while the isolator displacement and roof acceleration has mostly influenced by the eccentricity perpendicular to the earthquake path.


Dr. Ali Massumi, Dr. Kabir Sadeghi, Mr. Morteza Nekuei,
Volume 15, Issue 7 (10-2017)
Abstract

One of the main concerns in an essential or highly important building is finding the appropriate structural system, while the efficiency of each conventional structural system varies in different cases. In this paper a new multi objective structural configuration is proposed and its efficiency for protecting buildings against the multi-hazards including earthquake, explosion and typhoon is shown in a case study of a 10 stories building sample. To create the optimum and efficient configuration of the structural elements, and to make some large spans, a configuration including Vierendeel girders is used. In this type of configuration, the inner suspended floor parts protect the outer elements by balancing perimeter span loads. This system makes a new condition for the building to be protected against the progressive collapse due to the terrorism attacks. Furthermore, the partially suspended floors in special stories act like tuned mass dampers (TMDs), which are suitable to decrease the amplitude of the displacement response of the structure during an earthquake.



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