جستجوی مقالات مرتبط با کلیدواژه « Lead Rubber Bearing » در نشریات گروه « فنی و مهندسی »

AbstractIn the present study, the evaluation of the seismic performance of steel framed buildings on two types of seismic isolation systems under far-fault earthquakes has been investigated. The isolator used are lead rubber bearing and single arc friction pendulum system. In order to compare the behavior of these isolators, the effective time period is considered as one of the most important properties of the isolator. The effective time period of the isolators is 2.5, 3.5 and 4.5. Three types of steel framed buildings with special moment resistant steel frames of 3, 7 and 12 stories are placed on these isolators. These three buildings represent low-rise, mid-rise and high-rise buildings. The effect of these two types of seismic isolators has been investigated in reducing the acceleration response and the relative displacement(drift) of the floors. The results show that the efficiency of both types of lead rubber bearing and single arc friction pendulum system decreases with the increase in the height of the building. The efficiency of the single arc friction pendulum system is 14% lower than that of the lead rubber bearing. Increasing the target natural period (decreasing the stiffness of the isolator) in reducing the response of the buildings in the lead rubber bearing has an average of 27% better performance than the single arc friction pendulum system.

Isolators and dampers are devices that dissipate energy and reduce the seismic response of structures during strong earthquakes. Lead Rubber Bearings (LRBs) and Tuned Mass Dampers (TMDs) are two common types of these devices. Studying non-linear behavior and seismic properties of structural systems equipped with this type of isolators and dampers can significantly enhance understanding of their behavior against lateral forces caused by strong earthquakes. In this study, a 9-story steel structure was analyzed using the Endurance Time Analysis (ETA) method in SAP2000 software with fixed and isolated bases, along with a tuned mass damper with different mass ratios and without a tuned mass damper. The analysis results indicate that the tuned mass damper is highly effective in reducing the displacement of the isolator level, drift ratio, and story shear forces. This effect is more significant with higher mass ratios of the TMD. This effect is more pronounced with higher mass ratios of the TMD. However, reducing the absolute acceleration response of the structure has not been effective, and increasing the mass ratio of the TMD only reduces the performance of the control system in improving the absolute acceleration response compared to the isolated state.

Recently, base isolation techniques are applied as a resisting system to protect the structures from seismic and dynamic loadings. Due to their importance, in this paper, an optimum arrangement of lead rubber bearing (LRB) and friction pendulum system (FPS) is investigated in irregular buildings and its performance is compared with a regular case. For this purpose, 3 types of irregularities have been adopted. Accordingly, 3, 7 and 10 story buildings have been performed and 12 possible combination have been applied for the isolators in each model. Afterwards, the numerical models have been analyzed using nonlinear time-history analysis and direct integration method and applying 7 earthquake records along the longitudinal and transverse directions of the building. The obtained results of the numerical study show that the application of FPS and LRB isolators in outer and inner columns respectively, led to a better performance compared to the other arrangements by reduction of the inter-story drifts as well as base shear and enhancement of the energy dissipation which is due to the characteristics of FPS isolators in balancing the applied forces with the building’s mass and prevention of torsion occurrence in irregular structures. Unlike the irregular buildings, application of FPS and LRB isolators in inner and outer columns, result in a better performance by reducing the story drifts in regular structures.

Dampers and isolators are energy dissipating devices to control and reduce the seismic responses of structures under strong earthquakes. One of the most widely used of these devices is a special type of damper called TMD mass dampers and LRB lead core separators. Tuned Mass dampers (TMD) and Lead Rubber Bearings (LRB) are of the most widely used types of these devices. The scientific study of the seismic characteristics and nonlinear behavior of structural systems equipped with this type of dampers and isolators can significantly help to understand the behavior of these systems against the lateral forces imposed by strong earthquakes. In this research, a 12-story concrete structure with mass damper with various mass fractions, without isolator and with lead core isolator is designed. Then, applying time history analysis in SAP2000 software in isolated states without damper and with damper with different mass fractions, the responses of the structures against the mentioned earthquakes are obtained. The results of the analysis presented that the presence of mass damper is very effective due to the increased displacement in the isolated level. This effect is increased by increasing the mass fraction of the damper. The seismic isolator, on the other hand, can reduce the relative displacements of stories by 20 to 30% on average. The mass damper controls the large displacements of the isolator. The results in the studied structure revealed that in order to utilize the maximum capabilities of the isolator, it should be combined with mass damper.

In this research, numerical analysis of the hybrid lead rubber bearing system with shape memory alloy was investigated by Abaqus software and the effectiveness of various parameters on its performance was examined. The parameters studied are the bearing dimensions, the type of shape memory alloy and its cross-sectional area, the lead core diameter, the thickness of the rubber layer and the compressive stress. In this hybrid bearing, memorable form shape memory alloy are used as a recovery unit and lead core is used as a unit of energy dissipation. For this purpose, a finite element model of the bearing is modeled using the Abaqus software and the effect of the various parameters mentioned on the bearing performance has been investigated. The results show that the structures equipped with this bearing have better seismic performance than lead rubber bearing. Finally, depending on what kind of performance is required from the bearing, the parameters can be obtained optimally. As a result, in order to achieve a combination of behavior, both the suitable absorption capacity of lead and the recentring property of the shape memory alloy, it is necessary to balance the stiffness between the lead core and the shape memory alloy wire.

The present paper investigates the operation of the sliding mode on three-dimensional benchmark building with smart base isolation to reducing the dynamic responses of seismically excitation. According to the being three-dimensional, interweaving responses of the structure with each other, cohesiveness of behavior of superstructure and base level and computing the nonlinear force of base isolation systems, this building is very complex. Under these circumstances, we used extended sliding mode theory to applying the benchmark building. Also, the actuators are located only at the base level and in the two main directions. The results indicate that the proposed control system improved the building responses.

By examining the results of the analysis of the modification factor of the bridge with LRB isolators for x and y, respectively 2.32 and 3.95 and modification factor of bridge isolators ERB to x and y, respectively 2.57 and 4.25 was calculated. So modification factor of the bridge with LRB isolators for x and y is less than ERB isolators that represents the LRB bearings will cause that substructure is less inside nonlinear phase. Also the modification factor is less than the factor of “Publication 463” –it is in the x and y respectively 3 and 5- that indicates isolators reduce the nonlinear behavior of structural parts and lower general modification factor of the structure. The modification factor of isolators of bridge is less than the amount listed in the code. Although there is no significant difference but it less of it can be a reason for further investigation and as well as selected and proposed new factors for bridge with isolators in the codes.
In addition, the effect of reduction in the spans can be seen in two cases that there is no significant effect in various spans of bridge.

Conventional methods for seismic design of structures are based on building capacity. Because of the disadvantages of conventional methods, base isolation system is known as an effective solution to protect structures against earthquakes. In this study the operation of 2-storey steel frame with and without seismic isolators Under near-fault earthquake of chichi، northridge and capemendocine Are investigated. Effect of characteristic strength to structure weight ratio is also evaluated and performance of braced frames and moment frames with lead core isolators are compared. The results indicate that seismic isolators will lead to better performance of structures against earthquakes and characteristic strength to structure weight ratio have a significant impact on the performance of the structure.