Tesis doctoral de Arash Bahar
In structural engineering, one of the constant challenges is to find new better means of protecting structures from destructive environmental forces. One approach is seismic isolation, which has shown to not only reduce the response of the primary structure, but also reduce damage to equipment and other non-structural secondary elements. A drawback of most isolation systems appears when one considers the response of isolated structures subjected to earthquakes characterized by near-field motions. Such motions are likely to produce large isolation deformations, which may lead to buckling or rupture of isolators. To control these large deformations one way is to utilize supplemental dampers together with the isolation system (a hybrid system). However the benefits of isolation system may be significantly reduced for both moderate and strong earthquakes due to the transfer of energy into higher modes which can result in increased interstory drift and floor accelerations. One approach to improve the performance of an isolation system is to incorporate devices within the isolation system whose properties can be adjusted in real-time during earthquakes. Such devices are referred to as semi-active. The control forces in semi-active systems are developed as a result of the motion of the structure itself. They can only be modified through appropriate adjustment of mechanical properties of semi-active devices. furthermore, the control forces act to oppose the motion of the structural system and therefore promote the global stability of the structure. specifically the mr dampers appear to have significant potential to advance the acceptance of structural control as a viable means for dynamic hazard mitigation. However, because of the inherent nonlinearity of mr dampers, the first step in the design of a semi- active control is the development of an accurate model of the mr device. The system-identification issue plays a key role in control problems. the nature of this research is multidisciplinary because it deals with two concepts, identification of a mechanical device (mr damper) as well as a structural control problem in a civil engineering perspective. As a first step, a new bouc-wen based normalized model has been developed to study the behavior of a wider range of mr dampers, specially the devices which can be more effective in the vibration control of real civil engineering structures (large-scale mr dampers). Based on this new model, an extension of a parameter identification method for mr dampers has been proposed. This extension allows to identify a larger class of mr dampers more accurately. The validation of the parameter identification method has been carried out using a black-box model of an mr damper that is a part of a smart base-isolated benchmark building model available in the community of researchers in structural control. The versatility of the parameter identification method has been tested using the mr damper as a semi-active device under time-varying voltage and earthquake excitation. Then, based on the proposed extended bouc-wen based normalized model, a new inverse model for mr dampers has been proposed. If two additional practical physical constraints are satisfied, then the voltage of the mr dampers can be manipulated by the inverse model. finally, a hierarchical semi-active control strategy for the control of the vibration response of the isolated buildings equipped with a set of parallel mr dampers has been presented. This strategy consists of four steps applied in real time at each control instant: 1. Compute the overall desired control force to be applied at the base of the structure. 2. Determine the total force applied at the current control instant by the set of mr dampers. If this force is smaller than the desired force and they have the same sign, this means that the mr dampers need to apply more damping force and go to step 3. otherwise the voltage of the mr dampers is set to 0. 3. Determine the number of dampers that are applying force in the same direction as the desired control force. 4. Compute the corresponding command voltage for each mr damper using the inverse model. the whole method is simulated by considering the three-dimensional smart base-isolated benchmark building which is also used by the structural control community as a state-of-the-art model for numerical experiments of seismic control attenuation. The resulted performance indices demonstrate that the proposed semi-active method can effectively improve the performance of the building under earthquake loading.
Datos académicos de la tesis doctoral «Hierarchical semiactive control of base-isolated structures«
- Título de la tesis: Hierarchical semiactive control of base-isolated structures
- Autor: Arash Bahar
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 03/07/2009
Dirección y tribunal
- Director de la tesis
- José Rodellar Benedé
- Tribunal
- Presidente del tribunal: Francisco López almansa
- amadeo Benavent climent (vocal)
- Carlos Moutinho (vocal)
- ningsu Luo ren (vocal)