جستجوی مقالات مرتبط با کلیدواژه "seismic isolator" در نشریات گروه "عمران"

The application of seismic isolators at the base or mid stories by employing the mechanism of tuned mass dampers (TMDs) in structures provides an effective seismic control method for buildings. In this study, three prototypes of 10-story steel moment-resisting frame structures with intermediate ductility that are designed in accordance with second and fourth editions of Iranian Seismic Design Code (Standard No. 2800) as well as the second edition with one story on seismic isolator at the last floor were designed and modelled using nonlinear static pushover and nonlinear dynamic time history analyses under three far-fault earth‎quakes. The results were presented in the form of pushover curves and time history of roof displacement, base shear, maximum drift and roof acceleration of stories to compare the seismic enhancement of roof-level isolating technique and the effectiveness of the seismic criteria of Standard No. 2800. The results of research indicated that adding on isolated story at roof level had a significant effect on decreasing the drift of the stories. This reduction for the designed structure based on the second edition of Standard No. 2800 is down to an average maximum of 25%. In addition, using seismic isolators reduces the base shear by 30%. The decrease in the amount of roof displacement is also 40%. Also, the results showed that the efficiency of isolated story application as the last story to reduce the damage.

There are different ways to design energy dissipators. According to the type of performance of these elements, it is better to adopt the design method according to the consumed energy in order to determine what load should be considered as the design load for the energy-dissipating elements so that these elements have the best seismic performance. One of these methods is the use of energy-based performance index. This method is usually used to design pall friction dampers. In this research, it has been tried to use this method for a 12-story reinforced concrete structure of friction dampers, viscous, and seismic isolators of the lead rubber support type, and their performance is investigated. Based on this, for the earthquake records, the energy-based performance index has been calculated and the optimal design load has been calculated for these three energy wasters. Structures with optimal design load are subjected to dynamic loads and the contribution of elements in energy loss and their fragility curve have been evaluated. The results show that in a constant spectral acceleration (Sa), the probability of exceeding the specified performance level of a structure with a friction damper that is designed on this basis is lower than other structures. Also, in the acceleration of the design, the seismic isolator has wasted more energy than the other two structures.

One of the effective methods to reduce the impact of earthquakes on structures and improve the seismic performance of structures is the use of seismic isolation system. In this paper, the seismic performance of asymmetric isolated structures with different bracing systems under near-fault strong ground motions is investigated. Nonlinear dynamic analysis are performed under the simultaneous application of horizontal and vertical components of seismic acceleration. For this purpose, three types of chevron, cross and zipper bracing systems in 5 and 10-story structures with 0%, 10% and 20% mass eccentricity have been studied. Nonlinear time history analysis is performed by seven selected accelerogram. First, the symmetrical structure was analyzed in fixed and isolated base states. Then, the asymmetric effect on two eccentricity cases 10% and 20% in the target structures was compared. The average of shear force, drift and rotation of floors and input energy to the structure are the parameters studied in this paper. With an increasing eccentricity of the structure, the energy absorption by the isolator is reduced and the base shear is increased. Among the different bracing systems, the energy absorbed by the isolation system in the structure with zipper bracing increased by 53% and the base shear rate decreased by 80%.Based on the analysis results, base-isolation in the structure with cross-bracing in symmetrical, and asymmetric has caused a reduction of more than 70% of the floor rotation compared to other bracing systems.

One of the common methods in controlling the seismic response of structures is the use of seismic isolators. Isolators reduce the base shear as well as the relative displacement of the floors by increasing the period of the structure. Typically, extreme deformation of the isolator level occurs due to severe environmental factors, which can lead to damage to the isolators; As a result, there is a possibility of permanent deformation in the isolator and also the collision of the structure with adjacent buildings. Therefore, to prevent damage to buildings equipped with base isolations due to severe ground motions, it is important to identify damage at the isolators. In this study, assuming the linear behavior of the main structure, a proposed subspace-based method for identifying the stiffness of the base isolation with a limited number of sensors is presented. For this purpose, using the compression technique, the structure equipped with a separator with a large number of degree of freedom (DOF) is transformed into a two DOF structure; So that the stiffness associated with the first DOF in the reduced system corresponds to the stiffness of the Isolator level in the original structure. Then, using the identified Markov parameters of the system, the reduced structural stiffness is identified. Numerical examples are used to evaluate and compare the performance of the proposed method. The results show that even in the presence of noises in the measured responses, the proposed method detects the amount of damage at the isolator level with acceptable accuracy.

In this paper, the seismic behavior of base-isolated water storage tanks under the effect of long-period earthquakes has been investigated; as relatively high period of these types of structures causes them to be sensitive against long-period earthquakes. In this regard, an efficient and new method called critical excitation method (CEM), is employed for seismic behavior of base-isolated water storage tanks, for the first time. In the CEM, it is tried to produce critical earthquakes for each structure based on its characteristics and parameters, and then apply them to the undertaken structure so that the seismic behavior of structures during and after the earthquake may be increased. To investigate behavior of base-isolated water storage tanks under long-period earthquakes, three types of broad, middle and slender storage tanks have been used, for which two types of isolators (i.e., lead rubber bearing (LRB) and friction pendulum system (FPS)) are equipped. In order to model seismic behavior of water storage tanks considering fluid-structure dynamic interaction effects, a simplified and practical model proposed by Haroun has been employed in this research. The base-isolated water storage tanks have been exposed to long-period earthquakes to magnify responses. In addition, in order to develop the CEM, it has been used to analyze base-isolated water storage tanks through modifying available matrices in the equation of motion, rewriting the required formulas and developing the necessary codes in MATLAB environment. According to the results obtained from this research for the specific cases considered, it was found that using energy dissipation systems has caused these structures to perform better. Moreover, by proposing the CEM, this method was investigated for the first time with regard to base-isolated water storage tanks. In addition to introducing the critical parameters of this method, it was found that using this method leads to critical conditions in base-isolated water storage tanks.

Seismic isolation is one of the best-advanced methods for controlling seismic vibrations in buildings, bridges and nuclear facilities. A new Friction Multi-Layer Elastomeric Seismic Isolator (FMESI) has been modeled, analyzed and investigated by ABAQUS finite element analysis software and then, compared to real models. A number of friction cores have been used instead of the lead core therefore, some of the previous isolator problems have been almost resolved. Moreover, Studies show that the proposed isolator provides suitable initial stiffness and acceptable hysteresis behavior under different vertical and horizontal loading conditions and also internal stresses in different layers are acceptable. Also, as a result, , the initial stiffness and overall area of the curves increase, as friction coefficients of the cores increase, although the frictional coefficients must be within a certain range

Seismic loads may damage municipal solid waste landfills (MSWLF) through the relative movements within the waste, bottom lining system, cover system, foundation, and interfaces. The smooth synthetic materials might be placed beneath the structures to provide seismic protection by absorbing the imparted energy of earthquakes through the sliding mechanism. In the present study, experimental investigations were conducted in order to evaluate role of in-soil base isolation on seismic response of the Kahrizak MSW landfill. Shaking table tests were conducted on the MSW embankment isolated by semi-elliptic shaped liners and subjected to harmonic sinusoidal base excitations. Furthermore, the shaking table model was simulated by numerical analysis. The results of the isolated and non-isolated cases are compared in terms of permanent displacement and seismic response. Subsequently, the behavior of the numerical model was evaluated for different parameters. A reasonable agreement was found between the results of the physical model and the numerical model in prototype scale. The efficiency of in-soil isolation increases with increasing the amplitude of input motion. The results show that increasing the shear modulus reduces the amount of spectral amplification and relative displacement. It was also observed that as the age of the MSW increases, base isolation increases the displacement and crack width. Moreover, employing flat liner facilitates the movement of the ridge to the sides; and the concave liner prevents the wedge to move and, hence the quantity of settlement is reduced.

The response of bridges to abnormal loads have always been significant in structural engineering, especially in progressive collapse analysis. In this paper, the performance of bridges, undergoing progressive collapse, with and without isolator is investigated. Nonlinear time history analysis is used to obtain maximum responses of the structure by considering two different damage scenarios. In the first scenario, it is supposed that the side column of the bridge is collapsed and therefore is detached from the structure while in the second one, the middle column is removed. Accordingly, several models with rubber-sliding isolators, designed according to AASHTO standards are analyzed using OpenSees software. Moreover, the friction parameter of the isolator is considered as a variable in terms of the sliding velocity and acting vertical load. Results show that isolator yield doesn’t occur in both scenarios and subsequently the sliding of the bridge deck is not observed. However, a permanent displacement in the first scenario is detected because of instability of the bridge deck. It can also be noted that in most cases, using seismic isolators results in the growth of the maximum responses.