Buildingstructures generally contain inherent low damping capability and hence are vulnerable to seismic excitations. Control devices are therefore playing a useful role to provide safety to buildingstructures subject to seismic events. Passive, active and semi-activedampers are commonly used in buildings as control devices. In recent years semi-activedampers have gained a considerable attention. Magneto-rheological (MR) dampers, a type of semi- active damper, have proven to be quite effective in seismicmitigation of buildingstructures. MR dampers contain a controllable MR fluid whose rheological properties vary rapidly with the applied magnetic field. Although some research has been carried out on the use of MR dampers in buildingstructures, optimal design of MR damper and combined use of MR and passive dampers for real scale buildings have hardly been investigated. This thesis generates data for incorporating MR dampers and MR-passive damper combinations in buildingstructures in order to achieve acceptable seismic performance. The MR damper model was developed integrating control algorithms commonly used in MR damper modelling. Developed MR damper was integrated in to seismically excited structures as a time domain function. Linear and nonlinear structure models are evaluated in real time scenarios. Analyses are conducted to investigate the influence of locations and number of devices on the structure’s seismic performance. This research provides information to design and construction of earthquake safe buildings with optimally employed MR dampers and MR-passive damper combination in use.
A hierarchical semi-active control strategy has been presented in this paper, and has been applied to the control of the vibration response of a numerical three-dimensional benchmark building. A new inverse model of an MR damper has also been proposed to overcome the difﬁculty of commanding the MR damper to output the desired control force. This inverse model is based on (a) the ex- tended normalized form of the Bouc–Wen model for MR dampers and (b) two simpliﬁcations on the parameters of the model. With respect to the implementation issues, a new practical method has been deﬁned to compute the command voltage of each damper independently according to the desired control force: the manage- ment of these MR dampers is based on a hierarchical strategy. The whole method is simulated by considering a three-dimensional smart base-isolated benchmark building which is used by the struc- tural control community as a state-of-the-art model for numerical experiments of seismic control attenuation. The performance indi- ces demonstrate that the proposed semi-active method can effec- tively suppress structural vibration caused by earthquake loading and can provide a desirable effect of structural performance.
For bridges, wind also becomes the most important effect as the bridges become longer. Another issue is the ground vibration caused by the humans and the vehicles and for that very reason when a troop is crossing a bridge they have to break the rhythm of their steps, otherwise it can excite the structure at its resonant frequency which can lead to significant vibrations. Similarly, if there is a gym on the ground floor of a building, when in heavy use, these activities can also lead to noticeable vibration in the structure. In the early days, researchers have focused mainly on using passive damping techniques to deal with vibration in civil structures. They are still used, but provide less vibration reduction than either active or semi-active devices. An advantage of passive dampers is that they do not require external power to operate. Different passive dampers
devices in structural system has gained momentum. To keep the vibration of these structural systems within the functional and serviceability limits and to control and reduce structural and architectural damage caused by the extreme loads, different passive-, semiactive-, active- and hybrid- devices and design methodologies are being developed. Addition of supplemental passive devices and semiactive energy devices such as VFDs and MR dampers are considered to be viable strategies for enhancing the seismic performance of buildingstructures. Several researchers have carried out theoretical and experimental studies on passive and semi-active vibration control systems.
Abstract- Vibrations due to natural dynamic loads generated by earthquake. The reducing of structural vibrations occurs by adding a mechanical system that is installed in a structure called Dampers .In this paper, the vibration control of multi degree of freedom (MDOF) buildings connected with selected types of dampers due to earthquake effect is studied. The application of Viscous and Semiactive variable friction (SAVFD) damper for response control of seismically excited building is evaluated. Both dampers effectiveness is investigated in terms of the reduction of structural responses (displacements and accelerations) of the connected to building. The optimum number and the location of dampers are decided by the optimization procedure . The numerical study is carried out, namely (a) A MDOF building connected with viscous dampers with optimum damping coefficient (b) A MDOF buildings connected by Semiactive variable friction dampers with optimum gain multiplier. Results shows that using viscous and SAVFD to connect structures can effectively reduce earthquake-induced responses of either structure but when SAVFD is used to connect buildings and results shows that SAVFD can control only displacements of structures. Further, lesser damper at appropriate locations can significantly reduce the earthquake response of the coupled system. The reduction in responses when MDOF building connected with 50% of the total dampers at appropriate locations is almost as much as when they are connected at all floors, thereby the cost of the dampers can be minimized.
special attention as semi-active devices for mitigation of struc- tural vibrations. Because of the inherent nonlinearity of these devices, it is difcult to obtain a reasonable mathematical inverse model. This paper is concerned with two related concepts. On one hand, it presents a new inverse model of MR dampers based on the normalized Bouc-Wen model. On the other hand, it considers a hybrid seismic control system for buildingstructures, which combines a class of passive nonlinear base isolator with a semi-active control system. In this application, the MR damper is used as a semi-active device in which the voltage is updated by a feedback control loop.The management of MR dampers is performed in a hierarchical way according to the desired control force, the actual force of the dampers and its capacity to react. The control is applied to a numerical three-dimensional benchmark problem which is used by the structural control community as a state-of-the-art model for numerical experiments of seismic control attenuation. The performance indices show that the proposed semi-active controller behaves satisfactorily.
This paper presents a novel bracing system designed for earthquake risk mitigation for steel structures. It involves a rotary system which a Chebyshev linkage connected to the ground and the building frame. Upon earthquake excitation, movement of structure floor slabs causes a rotational motion in the disc. Displacement-based dampers are installed between the rotary system and the ground which damp the structural vibrations. The system amplifies the travel of the dampers and efficiency is enhanced. In addition, the cross-brace members are always in tension, permitting the use of very slender sections. The paper first reviews the governing equations of the system, followed by a physical model demonstration. A 3-degree- of-system model with the proposed rotary system was subjected to simulated ground shaking. Acceleration on top floor was measured. Results demonstrated that proposed system effectively supresses the vibrational characteristics of the structure, and represents a viable and inexpensive solution to mitigate seismic risks.
In this paper, a NN model is used to emulate the inverse dynamics of the MR damper. This NN model (NIMR) is trained based on the input-output data generated using the phenomenological model proposed by Dyke et al. . The model calculates a voltage signal based on a few previous time steps of velocity, damper force and desirable control force. This NN model is used to calculate voltage signals to be input to the MR damper so that it can produce desirable optimal control forces that are estimated by the LQG control algorithm. In principle, these control forces can come from any control algorithm that requires an explicit use of control forces to mitigate response. The eectiveness of the NIMR is illustrated and veried using the simulated response of a full-scale, nonlinear, seismically excited, 3-story benchmark building excited by several historical earthquake records. The semi- active system using the NIMR model is compared to the performance of an active LQG and a Clipped Optimal Control (COC) system, which are based on the same nominal controller used in the NIMR control algorithm. Additionally, two passive control systems are also considered and compared.
Piezoelectric (PZT) dampers utilize PZT materials (most commonly ceramic or crystalline in structure) that react to the application of electric current and generate a significant amount of strain/stress, the level of which can be adjusted through the level of current applied. These materials are utilized as stack actuators (an actuator consisting of a stack of PZT material that provides displacement when current is applied) or in active struts (linear actuators with variable stiffness). Kamada et al. [ 139 ] use PZT stack actuators to mitigate vibrations through control of bending moments in columns for a scaled, four-story, 3.7-m tall steel frame with a rectangular plan. They tested two different placement schemes on a shaking table subjected to sinusoidal loadings: one with eight actuators placed vertically under the base of each column at ground level and another with four actuators placed vertically at the base of the column at ground level, and four between the first and second floors. The authors found that both placement schemes performed similarly using the H ∞ control algorithm. Udwadia et al. [ 140 ] usesemi-active members consisting of PZT stack actuators to control simple MDOF systems. Xu et al. [ 141 ] use PZT actuators and an LQR controller to reduce large displacements of the top machinery room of a 30-m tall, 57.8 by 119.7 m in plain ship lift under seismic excitation. Chen and Chen [ 142 ] present a power-saving control algorithm to manage the response of a benchmark 20-story model, using PZT actuators in cross-bracings subjected to 1995 Kobe, 1940
The paper discusses the “software”-optimisation of a novel, energy-, cost- efficient hybrid semi-active tuned mass damper configuration applicable to earthquake and wind structural vibration mitigation. Namely, an arrangement of both active and semi- active vibration control components coupled with a range of practical-to-use control algorithms are assessed towards an optimal and fail-safe holistic solution. For brevity, the testbed is the simplest sway single-degree-of-freedom structure under harmonic loading. The analysis for the hybrid vibration mitigation device builds on top of previous findings on the effects of control constraints, such as the stroke and force saturation limits, on the effective structural damping performance. The outcome produced is a hyperstable control solution that while waiving the cumbersome requirement for full-state feedback enables superior performance both in terms of response and energy demand. Essentially such an option satisfies both strict serviceability and sustainability requirements that are often found to govern modern structural applications, yielding a practical, reliable option with broad applicability and efficiency.
CFD was proposed by Mirtaheri et al.  as an innovating type frictional damper which does not use bolts or any other pretention element to induce friction between contact surfaces. CFDs consist of two main parts, the internal solid shaft (Fig.1a) and the external hollow cylinder (Fig.1b). A longitudinal section of the CFD is shown in Fig.2a. The inner diameter of cylindrical element is slightly smaller than the diameter of the shaft at the contact length namely L0. Heating the cylindrical part its diameter will increase due to thermal expansion and the unheated shaft can be easily placed into the cylinder.
of suspension bridges is a complicated problem which is out of the scope of this paper. For more information on dynamic behavior of the suspension bridges, readers are referred to the studies performed by Abdel-Ghaar and his co-authors . The motion equation of these bridges can be written using nite element method and Hamilton's energy principles [28,30]. The main objective of the present study is to control the vertical vibration response of suspension bridges using MR dampers, and to nd the optimal solutions for dampers' numbers and locations. To study the performance of the MR dampers in reducing the vertical response of these bridges, it is assumed that the bridge is subjected to vertical component of the earthquake acceleration transmitted to the bridge deck by the piers/ abutments. For numerical simulation of the bridge responses, 15 world-wide ground motion vertical accelerogrames, shown in Table 1, are used as the input excitations. The accelerogrames are chosen, such that a variety of Peak Ground Accelerations (PGAs), fre- quency content levels, and distance to fault rupture can be taken into account in the study. Static condensation  of the stiness matrix is performed to eliminate the bending rotational degrees of freedom, and then the mass of each element is equally concentrated on its end nodes, resulting in a diagonal n n lumped mass matrix where n is the total number of vertical degrees of freedom [4,28]. Finally, the equation of motion of the uncontrolled bridge can be written as follows :
polymer (FRP) jackets for use in confining RC columns and joints. In particular, in flat- slab structures, punching shear failures are likely to occur if the slab is not designed for the combined effects of lateral and gravity loads. Therefore, local retrofits are mainly performed on slab-column connections. Recently, research related to member-level retrofits in the U.S. has actively investigated columns, beam-column joints, and slab- column joints (Harries et al. 1998, Luo and Durrani 1994, Farhey et al. 1993, Martinez et al. 1994).
Abstract There are many passive energy dissipating devices designed to dissipate earthquake energy in a structure. Metallic yielding dampers is one of these devices which are very efficient as they dissipate seismic input energy through hysteretic behavior. This research used ETABS software to analyze the performance of three metallic yielding dampers; X-shaped damper, Double X-Shaped and Comb Teeth Damper. The storey response data obtained from the analysis is storey shear. Each damper has three types of material; A992 steel, A36 steel and Aluminium. Concentrically braced steel frames with Chevron bracing were used and the dampers were placed in brace to beam orientation in each frame. The two types of frames analyzed were; low rise building with five storeys and a high rise building with twenty storeys. The site locations for both structures were in the region of California in the United States of America. The structures were analyzed by subjecting them to two earthquakes Loma Prieta and San Fernando as they were two of the major earthquakes that struck California in the nineties.
Tuned Mass Damper (TMD) is a devises which combination of a mass, a sprig and a damper that attached to structure for reducing the dynamic response of structure. They work on the principal that the frequency of damper is tuned to particular structure frequency. energy is dissipated the damper inertia force acting on the structure. The properties of dampers are calculating by the following formula.
Most used dampers are fluid dampers, just like the shock absorbers in vehicles. Fluid viscous damper is composed of a piston head, a piston rod and a cylinder full of a viscous fluid. Fluid viscous damper that operates according to the principle of flow of fluid through orifices. When in the damper, piston connecting rod and piston head strokes, forcefully fluid flows through orifices by creating differential pressure across the piston head, will produce very forces that resist the relative motion of the damper (Lee and Taylor 2001).
Structural analysis is the judgment of the effects of loads on physical structures and their segments. Structures subject to this type of analysis include all that must withstand loads, such as buildings, bridges, vehicles, machinery, furniture, attire, soil lamina, prostheses and biological tissue. Structural analysis engages the range of applied mechanics, materials science and applied mathematics to compute a structure's deformations, internal forces, stresses, support reactions, accelerations, and stability. The results of the analysis are exercised to check a structure's vigor for use, often preventing physical tests. Structural analysis is hence a key component of the engineering design of structures as described by K. H. Chang in 2009.
systems have been proposed to raise the seismic design of structures. Among these, friction damping has shown great potential. Friction dampers are designed in such a way that there moving parts slide over each other during a major earthquake. Major reason of sliding is to create a friction that uses some of the energy from earthquake that goes in thebuilding. Damper plays an important role in design of earthquake resistant structures. The main task of the structure is to bear the lateral loads and transfer them to the foundation. Using Push over analysis, the Response of the RC building is evaluated.
First analyses of the dynamic behaviour of the Reactor building, based on 3D finite element models, were performed in the period 1993 to 1995 within the frame of the Probabilistic Safety Analysis of Units 5&6, Level 1 . The generated complex spatial finite element model includes building structure and main heavy equipment – reactor vessel, steam generators, main circulation pumps, pressurizer, pipelines of the primary loop, etc. The influence of the soil-structure interaction was taken into account too. The soil basement was modeled by frequency independent springs and dashpots. In 1999 the generated FEM was enhanced and updated to be used within the scope of the Modernization program of Units 5&6. An improved numerical model was developed . The improvement was done in two directions. From one hand, a new more refined procedure for accounting of soil structure interaction was applied and, from the other, the influence of confinement pre-stressing on the dynamic behavior was accounted.