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Showing 19 results for Seismic Behavior

M.h. Baziar, Sh. Salemi, T. Heidari,
Volume 4, Issue 3 (9-2006)

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been performed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax=0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.
H. Shakib, F. Omidinasab, M.t. Ahmadi,
Volume 8, Issue 3 (9-2010)

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.

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.

A. A. Tasnimi, M. A. Rezazadeh,
Volume 10, Issue 3 (9-2012)

The torsional capacity of unreinforced masonry brick buildings is generally inadequate to provide a stable seismic behavior. The

torsional strength is believed to be the most important parameter in earthquake resistance of masonry buildings and the shear

stresses induced in the bed joints of such building’s walls is an important key for design purposes. Brick buildings strengthened

with wire-mesh reinforced concrete overlay are used extensively for building rehabilitation in Iran. Their quick and simple

applications as well as good appearance are the main reasons for the widespread use of such strengthening technique. However,

little attention has been paid to torsional strengthening in terms of both experimental and numerical approach. This paper reports

the response and behavior of two single-story brick masonry buildings having a rigid two-way RC floor diaphragm. Both

specimens were tested under monotonic torsional moment.Numerical work was carried out using non-linear finite element

modeling. Good agreement in terms of torque–twist behavior, and crack patterns was achieved. The unique failure modes of the

specimens were modeled correctly as well. The results demonstrate the effectiveness of reinforced concrete overlay in enhancing

the torsional response of strengthened building. Having evaluated the verification of modeling, an unreinforced brick building

with wall-to-wall vulnerable connections was modeled so that the effect of these connections on torsional performance of brick

building could be studied. Then this building was strengthened with reinforced concrete overlay and the effect of strengthening

on torsional performance of brick buildings with vulnerable connections was predicted numerically.

H. Tavazo, H. E. Estekanchi, P. Kaldi,
Volume 10, Issue 3 (9-2012)

Endurance Time (ET) method is a response history based analysis procedure that can be used for estimating the seismic response

of structures at different excitation levels in each response history. This seismic analysis method utilizes specific intensifying

acceleration functions to analyze seismic behaviors. One of the potential applications of the ET method is in the seismic

assessment of shell structures. In this study, a procedure for linear seismic analysis of shell structures is proposed and

applications of this method is investigated for several cases of shell structures. These structures are analyzed under three ET

acceleration functions in one direction and the results are compared to time history analysis considering seven actual earthquake

records. Moreover, the results of the ET method are compared to response spectrum analysis method. The outcomes of the study

reveal that the ET method predicts the linear seismic performance of shell structures with acceptable precision and significant

reduction in analysis time. Furthermore, it is conluded that scattering of results of three ET analysis is very low and one analysis

can be used instead of three. Finally, the comparison between THA and RSM results verify that response spectuarm method is a

conservative method which occasionally encounters problems to evaluate bending stresses of shell structures

A. Gholizad, P. Kamrani Moghaddam,
Volume 12, Issue 1 (3-2014)

High performance and reliability of refurbish able knee braced steel frames has been confirmed in previous researches trying to get an optimal design for its configuration. Buckling of diagonal member which affects the hysteretic behavior of KBF under cyclic loadings has not been foreseen in previous evaluations of this system. This deficiency can be improved by utilization of adjustable rotary friction damper device (FDD) as knee element. Diagonal element buckling can be prevented considering a suitable value for FDD sliding threshold moment Mf. Lower values of Mf Lower energy dissipation rate in FDD and this leads to an optimization problem. Nonlinear time history analyses have been performed in addition to lateral cyclic loading analyses to evaluate the response of single story KBF subjected to seismic excitation. Optimal Mf in FDD has been chosen according to these analyses results. Roof displacement and acceleration, base shear and diagonal element’s buckling status have been compared in optimally designed KBF and FDD utilized KBF (FKBF) with different configurations. Nonlinear dynamic analyses have been performed for one, four, eight and twelve story frames under different seismic records with several PGAs. More than 60% displacement response reduction has been earned for the FKBF without considerable increase in base shear.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)

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.
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.
J. Nazari Afshar, M. Ghazavi,
Volume 12, Issue 1 (1-2014)

The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.
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.
S.m. Zahrai,
Volume 13, Issue 3 (9-2015)

Seismic retrofit of masonry slabs in existing steel or masonry buildings has found special significance in current codes as failure of unstable jack arch slabs has been reported as a major reason for collapsing structures in Middle East deadly earthquakes. In this paper, three retrofit schemes are investigated and compared. The proposed rehabilitation techniques consist of a single X strapping, SXS, a double X strapping, DXS, and a two-way jack arch slab supported by a steel grid. Using experimental studies, advantages and disadvantages of each scheme are evaluated. In-plane stiffness and capacity of the diaphragm are adopted as the seismic performance index of each rehabilitation scheme. According to the obtained results, the jack arch slab systems designed and constructed based on proposed retrofit methods provide an appropriate alternative to other forms of flooring in seismic zones. DXS can greatly improve diaphragm performance in terms of in-plane stiffness, capacity and even energy dissipation of the diaphragm compared with the other two techniques. The second place belongs to SXS while the steel grid scheme has a minor effect on the in-plane stiffness of the diaphragm.
L. Zeng, Q. Zhou, Ch. Xu, Y. Wu, X. Tu,
Volume 13, Issue 4 (12-2015)

To study seismic performance of concrete-encased composite columns with T-shaped steel cross-section, twelve half-scale columns were tested under quasi-stastic cyclic loading. The result indicates that concrete-encased composite columns with T-shaped steel section possess good seismic performance. The failure modes include bending failure, shear-bond failure, shear compression failure and shear-composition failure. Unsymmetrical phenomenon of positive and negative hysteresis loop was shown evidently. Span ratio has a great influence on failure mode. The ductility performance decreases with increasing of axial compression level. As stirrup ratio increases, ductility and bearing capacity of columns are improved greatly, and energy dissipation capacity after yielding is enhanced. Cross tie can enhance ultimate bearing capacity, and lower strength attenuation and stiffness degradation on the later loading stage

Guray Arslan, Muzaffer Borekci, Muzaffer Balci, Melih Hacisalihoglu,
Volume 14, Issue 3 (4-2016)

The contribution of concrete to inelastic deformation capacity and shear strength of reinforced concrete (RC) columns failing in shear has been investigated extensively by various researchers. Although RC members are designed to have shear strengths much greater than their flexural strengths to ensure flexural failure according to the current codes, shear degradation of RC columns failing in flexure has not been studied widely. The aim of this study is to investigate the shear degradation of RC columns using finite element analyses (FEA). The results of FEA are compared with the results of experimental studies selected from literature, and it is observed that the lateral load-deflection curves of analysed columns are compatible with the experimental results. Twenty-six RC columns were analysed under monotonically increasing loads to determine the concrete contribution to shear strength. The results of analyses indicate that increasing the ratio of shear to flexural strength reduces the concrete contribution to shear strength of the columns.

Mohammad Ali Hadianfard, Ramin Rabiee, Azad Sarshad,
Volume 15, Issue 2 (3-2017)

Microtremor measurement is a precise and applicable technique for evaluating structural dynamic characteristics and vulnerability index of historical buildings. In this research a historical citadel in Iran has been considered. Karim Khan Citadel (Arg-e Karim Khan) is a huge masonry structure which has been built in the 17th century in Shiraz, Iran. The plan of this building has a rectangular shape and has a circular tower in each corner. The height of each three story circular tower is 14 m and the height of walls between each two towers is 12 m. One of these towers has been swerved and for preventing its collapse, concrete was injected to the foundation of this tower. To study seismic behavior and vulnerability of the swerved tower and compare it with other straight tower, microtremor measurements were performed. Measurements were done on the center of each tower and its basement simultaneously. For determining natural frequency and damping ratio of each tower, Floor Spectral Ratio (FSR) and Random Decrement Method (RDM) were used, respectively. Results show that the natural frequency and damping ratio of the swerved tower are 1.9 Hz and 1.55 % while dynamic parameters of the straight tower are 2.12 Hz and 3.86 %, respectively. Also the towers frequencies are very different to the site frequency (4.18 Hz), therefore the resonance phenomenon isn’t probable. In addition, the vulnerability indexes of the swerved and straight towers were calculated 131.31 and 76.9, respectively, which shows that the swerved tower is more vulnerable.

Majid Mohammadi,
Volume 15, Issue 2 (3-2017)

Sliding foundations is a technique to suppress seismic loads applied to structures. There are many studies showing that sliding foundations are efficient specially for low rise buildings, however most of them have ignored the effects of vertical components of the earthquake records on the behavior of such bases. This paper focuses on influences of sliding foundations on seismic behavior of low rise buildings, for real cases. For this purpose, vertical component of earthquakes are considered as well as inherent properties of foundation material such as coefficient of Restitution (COR). Furthermore, variation of friction coefficient during the earthquake is considered. COR is utilized to consider bouncing of the structure after separation of the foundation, occurred for extreme downward vertical accelerations (greater than gravitational acceleration). Variation of friction coefficient is considered based on a new study, showing that the coefficient of friction depends on instantaneous amplitude and frequency of the vertical excitation. The obtained results show that vertical component of earthquake affects the behavior of the sliding base substantially. It is also demonstrated that providing material for the sliding base with higher COR is advantageous in decreasing structural acceleration response. Furthermore, the coefficient of friction is really lower than the regularly assumed values and therefore, leads to smaller structural acceleration response but mostly greater residual displacements.

Volume 15, Issue 4 (6-2017)

THIS IS THE REVISED VERSION OF THE PAPER A-10-581-3, CONSIDERED AS "MAJOR REVISION": One of the best methods to improve structural seismic behavior is to strengthen the infills by shotcreting. Most rehabilitation codes have a special part for masonry buildings and masonry infill panels. However they are completely silent for infills improved by concrete covers, probably for the lack of sufficient experimental test data. This paper focuses on the ultimate strength and modification factor of this type of infill panels, based on some experimental studies. The proposed formula of the existing codes for the equivalent width of the masonry infill panels is improved for the ultimate strength of shotcreted infill panels. It is also shown that the modification factors of the masonry and clay tile infill panels are downgraded and upgraded, respectively, if they are rehabilitated by concrete covers. The envelopes of the load-displacement behavior of the specimens are applied to calculate the modification factor, rather than the standard back bone curves. It is shown that they give more conservative values for the m-factor. Subsequently, some suggestions are proposed to estimate m-factor of shotcreted infill panels.

Xiaolei Chen, Jianping Fu, Feng Xue, Xiaofeng Wang,
Volume 15, Issue 4 (6-2017)

This paper presents a comparative numerical research on the overall seismic behavior of RC frames with different types of rebars (normal versus high strength rebar). A nonlinear numerical model is developed and is validated using experimental results. Comparing the numerical and experimental behaviors shows that the developed model is capable of describing the hysteretic behavior and plastic hinges development of the experimental RC frames with various strength longitudinal steel bars. The validated model is then used, considering the influences of axial load ratios and volumetric ratios of longitudinal rebars of column, to investigate the effects of reinforcement strength on the overall seismic behavior of RC frames. The simulation results indicate that utilizing high strength reinforcement can improve the structural resilience, reduce residual deformation and achieve favorable distribution pattern of plastic hinges on beams and columns. The frames reinforced with normal and high strength steel bars have comparable overall deformation capacity. The effect of axial load ratio on the energy dissipation, hysteretic curves and ultimate lateral load of frames with different strength rebars is similar. In addition, increasing the volumetric ratios of longitudinal rebars can increase the ultimate lateral load of frame and improve the plastic hinge distribution of frame.

Dr. Abazar Asghari, Mr. Behnam Azimi Zarnagh,
Volume 15, Issue 5 (7-2017)

For years, coupling shear walls have been used in  the mid to high-rise buildings as a part of lateral load- resisting system mostly, because of their ability to control the displacement of structures, Recently by changing the design codes from strength based design to performance based  design, nonlinear behavior of coupled walls became important for practical engineers, so that many researchers  are looking for ways to improve and also predict the behavior of coupled walls under severe earthquakes. This paper  presents  the results of   linear,  nonlinear static ( pushover)  and  nonlinear inelastic time-history analysis  of a 10-story  two- dimensional coupling shear wall (CSW) which is perforated with 3 different patterns which are taken from considering  the S22 stress of shell elements used for modeling shear walls,  nonlinear static analysis results confirm that perforation can increase the response modification  factor of coupled walls up to 33 percent and also the results of  linear analysis and design indicate that perforation can reduce the amount of reinforcement of coupling beams and other frame's  structural components. Also results of nonlinear inelastic time history  analysis confirm that by using perforation patterns the base shear- roof displacement hysteretic response get better and the  systems with perforation patterns can absorb more energy under severe earthquakes.

Hamid Reza Ebrahimi Motlagh, Alireza Rahai,
Volume 15, Issue 5 (7-2017)

This paper tried to analyze the behavior of a typical bridge and the effect of its skew degree on its behavior to near-field earthquakes. To this end, the seismic behavior of a number of typical bridges with same spans and different skew degrees was studied under near-field and far-field earthquakes. Non-linear static analyses (pushover analyses) were performed to determine the performance parameters of the bridge in each model. Non-linear time history dynamic analyses were also performed on the models to analyze the dynamic behavior and deformations of bridge components under near-field and far-field earthquakes. The responses of models, such as their displacement, base shear, and axial forces of columns to earthquakes under study are presented in the following sections. Results indicated that the base shear and displacement of the superstructure in near-field earthquakes without velocity pulse and far-field earthquakes are about or less than the corresponding values of the bridge performance point. Moreover, in the case of near-field earthquakes with velocity pulses the values of these parameters showed an increase. It was also revealed that an increase in the skew degree of the bridge led to an increase in the axial forces in columns and transverse displacement of the bridge.

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