The goal of the proposed project is to study the feasibility of a new variable stiffness isolator and to understand its behavior. The proposed system can function in passive and active modes, is fail-safe, and is very similar to the conventional passive elastomeric bearings. The power requirement is very low, and the system can be battery operated. The new system offers both passive and controllable components. The objective of this research is to understand the performance of the proposed variable stiffness isolation bearing. Prototypes of this system will be designed, fabricated and tested. For the proof-of-concept of its effectiveness under seismic motions, the proposed isolator will be examined on a scaled model building. Theoretical analysis will be carried out to model and predict the performance of the proposed system. Materials development will be focused on elevated working temperature, moisture resistance, and enhanced durability.
If successful, the proposed project will contribute to the advancement of passive-active protective systems for the control of large structures. Research in hazard mitigation of large structures is of high importance because it can significantly contribute to saving lives and resources. In recent years, considerable attention has been paid to enhancing the protection of civil infrastructure elements by taking advantage of new materials, high-tech devices, and advanced control methods. The activity will also provide advanced training in testing and analysis to the graduate student working on this project.
The goal of this project is to investigate the feasibility of a novel, fail-safe, variable stiffness and damping isolator (VSDI) as a base isolation bearing system. The proposed VSDI system consists of a traditional steel-rubber vibration absorber, as the passive element, and a MagnetoRheological Elastomer (MRE), with a controllable (or variable) stiffness, damping, and hysteresis behavior, as the passive-active element. To validate the capability of MREs and to demonstrate that these materials can be utilized as controllable protective devices, novel MRE materials as well as prototypes of VSDIs are developed, characterized, and tested. These studies are aimed to establish a fundamental understanding of the performance of the MRE-based VSDI bearing for a proof-of-concept evaluation in a small-scaled building. The performance of the prototype VSDI is investigated experimentally under dynamic shear tests. The experimental results show that the VSDI is capable of increasing its stiffness over 30% and at the same time damping properties for over 40% when it is fully activated by magnetic field. Both the stiffness and damping of the proposed device can be adjusted by the applied external magnetic field for possible application in a structural control system. The scaled building test setup consists of four VSDIs and four calibrated accelerometers to measure the acceleration of each floor as well as the ground motion. To investigate the performance of the VSDIs under the scaled building, sweeping sinusoidal vibration tests has been performed on the isolated scaled building. The response of the structure under a large range of sinusoidal excitations frequencies applied by a shake table has been studied. When the VSDIs are activated by only 1.0 Amp, the vibration frequency modes of each floor shift to the right. The major frequency shift effect occurs at first and second modes. This is very useful for tuned vibration control of a structure system under earthquake excitations, because most building structures suffer from near ground vibration at low frequency. Thus; the capability of the VSDI system to control the structural vibration is validated. The developed scaled building structure with four MRE VSDIs also provides a testing platform in the Laboratory for understanding the performance of the variable stiffness MRE device under semi-active control. A phenomenological model is developed for VSDIs. The constants of the model have been determined using the experimental transmissibility data of the VSDIs. Control simulation has been conducted and the performance of the control strategy has been studied. The scaled El Centro earthquake excitation is used as the input to the system, and the vibration mode is controlled by a Lyapunov-based control strategy. Shear experiments have been conducted on ASM standard MRE samples to observe the effect of iron particle polymerization on mechanical properties of MREs. Scanning Transmission Electron Microscopy and Atomic Force Microscopy have been performed on MRE samples to observe the quality of coating on iron particles. Control experiments have been performed on the isolated scaled building structure using the VSDI bearing and the results are processed. The shear properties of the VSDIs were investigated to examine and improve the proposed model. Using the experimental data, modification to the model has been proposed. To investigate the new model capabilities for dynamic performance of VSIDs, transmissibility experiments of the integrated system is simulated and simulation results are compared with experimental data. Finally results of the shear tests on MRE samples with coated and non-coated Iron particles are processed to observe the effect of oxidation on force deformation curves of MREs. The PSD of the scaled El-Centro EW is used as the input to the shake table. The applications of passive VSDIs reduce the maximum acceleration of the third floor of the scaled building for 43% while it increases the maximum displacement for 7% compard to fixed base condition. The on-state VSDIs reduce the maximum acceleration for an additional 7% and maximum displacement for 37% compared to the passive state. Finally, controlling VSDIs reduces the maximum acceleration for 17% while increasing the maximum displacement for 8 % compared to the on state. This indicates that the controlled state results in reduction in acceleration and displacement. Another advantage of using the controll strategy is less power consumption compared to on-state for 17%.
