Intl Institute of Earthquake Engineering and Seismology IIEES

Tehrān, Iran

Intl Institute of Earthquake Engineering and Seismology IIEES

Tehrān, Iran

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Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES | Farshadmanesh P.,Islamic Azad University at Tehran
ECCOMAS Thematic Conference - COMPDYN 2011: 3rd International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering: An IACM Special Interest Conference, Programme | Year: 2011

Sloshing is a well-known phenomenon in liquid storage tanks subjected to base or body motions. In recent years the use of baffles for reducing the sloshing effects in tanks subjected to earthquake has been studied by some researchers. However, the use of multiple baffles has not been taken into consideration so much. On the other hand, although some of the existing computer programs are capable to model sloshing phenomenon by acceptable accuracy, the full dynamic analysis subjected to random excitations such as earthquake induced motions is very time consuming, particularly when there are vertical and horizontal baffles inside the tank, which postpone the convergence of response calculations. Therefore, a simplified method for evaluation of sloshing effects in baffled tanks is desired. In this paper a method is presented for this purpose based on conducting several dynamic analysis cases, by using a powerful Finite Element (FE) method for rectangular tanks with various dimensions, subjected to both harmonic and seismic excitations, and then using neural network to create simple relationships between the dominant frequency and amplitude of the base excitations and the maximum level of liquid in the tank during the sloshing and also the maximum dynamic pressure on the tank wall. At first, the FE numerical modeling has been verified by using some existing experimental data. Then, dynamic analyses have been conducted to obtain the required numerical results for teaching the neural network. In the next stage, the neural network model has been developed. Finally, the predicted results of the neural network have been compared with those obtained by some other cases of analyses as control values, to make sure on the accuracy of the neural network model. The proposed simplified neural network model can be used also for finding the proper number and features of baffles for minimizing the sloshing effect on the tank for a group of given earthquakes, or other cases of base excitations.


Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES | Malek A.M.,Islamic Azad University at Tehran
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010

This paper discusses the optimum use of viscous dampers along the height of a multi-story steel building in order to minimize its seismic responses, based on the amount of 'received energy'. This is defined as the part of total input energy which refers to the positive work of the base shear force acting on the building foundation during an earthquake. For this purpose at first some typical steel buildings were designed based on the old versions of seismic codes in order to make them similar to the vulnerable existing ones. In the second step, various configurations were considered for dampers, including a) one damper just in one of the stories, creating n configurations, n being the number of stories in the building, b) m dampers (m= 2, 3, ..., n), each in one of the m uppermost stories, creating n-1 configurations, and c) m dampers (m=2, 3, ..., n-1), each in one of the lowermost stories, creating n-2 configurations. Various damping coefficient values were also considered for damper(s) in each of the above states to find out how this value affects the maximum responses. Besides, in each case, several earthquake accelerograms were used in the time history analyses to realize how the characteristics of earthquake are effective in the response values. Regarding that using dampers in various stories makes the damping matrix of the building non-proportional, a program was developed in MATLAB environment for calculating the seismic response of MDOF systems with nonclassical damping. Numerical results show that for any given earthquake a specific damping value leads to minimum received energy and base shear response almost in all combinations of dampers. Results also show that using two dampers instead of one causes a remarkable response reduction, while adding another damper leads to only a little more response reduction. Based on the results it can be said that by using just a few dampers in some stories it is possible to make the displacement and acceleration responses limited to some desirable level.


Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES | Behniafard M.,Islamic Azad University at Tehran
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010

In many provinces of developing countries there is just one single road connecting each city (or a sequence of cities) of the province to its central city. On the other hand, recent earthquakes have shown that roads are very sensitive either to direct effects of earthquakes or to their indirect effects resulting from the extensive use of the road for emergency response activities. Obviously, any blockage of a single road has very adverse short term and, and even long term effects on the response activities and restoration works after a major earthquake. On this basis, adding some redundancy to the road system by constructing detours in some particular sections of each road path can be a useful remedy. In this paper the possibility of using detours, and the benefits of using them for seismic risk reduction in the intercity road system has been studied, and a method has been proposed for this purpose. In the proposed method at first, the places in a road which have the potential of blockage due to earthquake are diagnosed. In the second step, among the location of high blockage potential those which have the possibility of detour construction are identified and classified based on the level of difficulty of detour construction work. A detour can substitute a single blockage location or several ones of them depending on how close together they are. In the third step, three following alternative mitigating measures are compared: a) retrofitting the vulnerable components or upgrading the seismic stability of vulnerable locations, b) preparing and storing the basic required tools and materials for construction of detours, where necessary, quickly after a major earthquake, and c) constructing the detours in advance. By comparison of these alternatives from economic and technical aspects, based on the experts' views using Analytical Hierarchy Procedure (AHP), the appropriate mitigating measure can be chosen.


Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES | Yousefi S.,Islamic Azad University at Tehran
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010

In this paper the roof isolation technique as a simple and easily doable method is introduced for improving the seismic behavior of masonry buildings. The basic idea is letting the roof to sit simply on the walls with not structural connection, so that the horizontal seismic forces between the roof and the walls can be transferred only by friction. Therefore, the maximum force transferred to the roof is limited to μ×g, where μ and g are respectively the friction coefficient and the gravity acceleration, and this in turn leads to decrease in the seismic forces acting on the building walls. To show the efficiency of the proposed technique, some masonry buildings were considered to be modeled and analyzed subjected to simultaneous effect of horizontal and vertical components of earthquake acceleration, with various frequency contents and different PGA levels. The simplified model of any buildings consists of an upper large block, representing the roof, resting on several small blocks, each one connected to two springs and two dampers. Each of these small blocks represents one of the building's walls. The upper block is in contact with lower blocks with a friction coefficient of μ, and the two springs connected to each of the lower blocks represent the walls stiffness values, either in in-plane or out-of-plane direction. The results show that by using roof isolation if μ is not greater than 0.3, the maximum shear forces of single-story masonry buildings, subjected to strong earthquakes, can be decreased between 30% to 50% depending on the earthquake characteristics, and the maximum roof acceleration is reduced more than 50%. Maximum displacement of roof with respect to walls is just a few centimeters in each direction. The vertical ground motion is effective on maximum response values, but, its effect is mostly negligible.


Ranjbaran F.,Islamic Azad University | Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES
ECCOMAS Thematic Conference - COMPDYN 2011: 3rd International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering: An IACM Special Interest Conference, Programme | Year: 2011

In this study the nonlinear finite element analysis has been employed to find out how the properties of ties, either vertical or horizontal, affect the seismic behavior of confined masonry walls. For this purpose the DIANA software (Version 9.3), which is powerful tool for numerical modeling of such structures, has been used. Among the parameters, which are believed to be effective in the confined wall seismic behavior, four ones relate to the ties. These include compressive strength of concrete used in tie elements, cross sectional area of ties, the amount of longitudinal reinforcement in vertical ties, and finally the rigidity of connections between horizontal and vertical ties. With regard to the amounts of the four mentioned parameters, the values recommended by the National Iranian Code of Practice for Seismic Design of Buildings (Iranian Standard No. 2800) were used as the bench mark values. The type of analysis conducted for the wall numerical samples was Push-Over Analysis (POA) and in all cases some reasonable value was considered for the amount of surcharge imposing on the confined wall due to the dead load of the corresponding floor. The results of POA were obtained by assigning various values, from very low to very high, to the four mentioned parameters, and the lateral force - displacement curves were plotted for each set of values. Numerical results show that with variations of the four parameters, considered for the ties' properties, between some limits the global behavior of wall changes slightly, however, if some of these four parameters get values beyond some limits the wall behavior changes drastically from one state to another.


Karimiyan S.,Intl Institute of Earthquake Engineering and Seismology IIEES | Moghadam A.S.,Intl Institute of Earthquake Engineering and Seismology IIEES | Vetr M.G.,Intl Institute of Earthquake Engineering and Seismology IIEES
Earthquake and Structures | Year: 2013

Margin of safety against potential of progressive collapse is among important features of a structural system. Often eccentricity in plan of a building causes concentration of damage, thus adversely affects its progressive collapse safety margin. In this paper the progressive collapse of symmetric and asymmetric 3-story reinforced concrete ordinary moment resisting frame buildings subjected to the earthquake ground motions are studied. The asymmetric buildings have 5%, 15% and 25% mass eccentricity. The distribution of the damage and spread of the collapse is investigated using nonlinear time history analyses. Results show that potential of the progressive collapse at both stiff and flexible edges of the buildings increases with increase in the level of asymmetry in buildings. It is also demonstrated that "drift" as a more easily available global response parameter is a good measure of the potential of progressive collapse rather than much difficult-to-calculate local response parameter "number of of collapse plastic hinges". © 2013 Techno-Press, Ltd.


Karimiyan S.,Intl Institute Of Earthquake Engineering And Seismology Iiees | Moghadam A.S.,Intl Institute Of Earthquake Engineering And Seismology Iiees | Husseinzadeh Kashan A.,Tarbiat Modares University | Karimiyan M.,University of Applied Science and Technology of Iran
International Journal of Civil Engineering | Year: 2015

Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers. © 2015, Iran University of Science and Technology. All right reserved.


Attarchian N.,Intl Institute of Earthquake Engineering and Seismology IIEES | Kalantari A.,Intl Institute of Earthquake Engineering and Seismology IIEES | Moghadam A.S.,Intl Institute of Earthquake Engineering and Seismology IIEES
Earthquake and Structures | Year: 2016

This research focuses on seismic performance of a class of single pier skewed bridges with three different pier-deck connections; skew angles vary from 0° to 60°. A well-documented four span continuous deck bridge has been modeled and verified. Seat-type connections with fixed and sliding bearings plus monolithic pier-deck connections are studied. Shear keys are considered either fully operational or ineffective. Seismic performances of the bridges and the structural components are investigated conducting bidirectional nonlinear time history analysis in OpenSees. Several global and intermediate engineering demand parameters (EDP) have been studied. On the basis of results, the values of demand parameters of skewed bridges, such as displacement and rotation of the deck plus plastic deformation and torsional demand of the piers, increase as the skew angle increases. In order to eliminate the deck collapse probability, the threshold skew angle is considered as 30° in seat-type bridges. For bridges with skew angles greater than 30°, monolithic pier-deck connections should be applied. The functionality of shear keys is critical in preventing large displacements in the bearings. Pinned piers experience considerable ductility demand at the bottom. © 2016 Techno-Press, Ltd.


Ranjbaran F.,Islamic Azad University | Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010

Using confined masonry buildings is very common in many parts of the world such as Europe, Asia, and Latin America as governmental and private buildings. Past earthquakes have shown the vulnerability of this type of buildings in several cases, however, experimental results represent ductile behavior of structural elements of such buildings, i.e. confined masonry walls. Design of buildings of this type is usually performed in a prescriptive manner without numerical modeling, and out of the framework of an analysis-designing process. The reasons behind this fact are firstly the lack of sufficient knowledge concerning the exact behavior and performance of such structural elements against the lateral forces, and secondly very time-consuming analysis procedures. The purpose of this research is to identify the major factors affecting the behavior of the confined walls against lateral and vertical forces, and then to present a simplified behavioral model precise, and at the same time, simple enough to be used by professional engineers. The proposed model can show the wall behavior before and after cracking. The required analyses have been performed by using DIANA (9.3) software, which is a powerful tool for numerical modeling of such structural elements. A series of nonlinear static analyses in parametric form has been performed using a wide range of effective factors on confined masonry walls with or without opening. Then, based on the numerical results, some simple formulas have been proposed to express the relationships between the lateral strength of the confined wall and the wall specifications, including the initial stiffness, the secondary stiffness after cracking, the ultimate strength, and ductility, to be used in engineering programs such as SAP, which are widely used in engineering firms, by practicing engineers.


Bonab A.P.,Islamic Azad University at Bonab | Hosseini M.,Intl Institute of Earthquake Engineering and Seismology IIEES
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010

The variation of input energy with characteristics of various structural systems, particularly in hysteretic states, has not been studied to such extent that creates enough confidence for proposing energy-based design criteria. In this paper, first a mathematical model for expressing the hysteretic behavior of structures is introduced, which has a simple mathematical form, and uses only three parameters, including the initial stiffness, the ultimate strength, and a parameter which controls the rate of change of curvature of the hysteretic curves. These parameters are all based on the real physical characteristics of structures. Then, to find out how the seismic input energy depends on the hysteretic characteristics of structures, a computer program has been developed in MATHEMATICA environment based on the proposed mathematical hysteretic model, and several time history analyses have been performed by using a variety of accelerograms. Regarding the three main parameters of the hysteretic model, three sets of analyses have performed in each of which just one parameter of the hysteretic model has been considered as variable to find out its effect independently. It should be noted that although the mathematical hysteretic model is simple, using it in a time history analysis program needs special attention to some criteria which should be met to keep the realistic behavior of the model. Numerical results show that in some cases the amount of input energy varies remarkably with the characteristics of the system, particularly the parameter which control the rate of change of stiffness. On this basis it can be claimed that this parameter can be used as a controlling tool for limiting the amount of earthquake input energy, and accordingly the level of overall damage to the structure.

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