Keywords: earthquake, friction damper, viscoelastic damper, non-linear dynamic analysis.

In order to control the vibration response of high rise buildings during seismic events, passive damping devices are most commonly used for energy absorption. Today there are several types of manufactured dampers available in the market, which use a variety of materials and designs to obtain various levels of stiffness and damping. Some of these include hysteretic, friction and viscous dampers. These dampers are usually installed between two load bearing elements (walls or columns) in new buildings. In existing buildings which require retrofitting, they could be installed in cut-outs of shear walls, as evidenced from recent investigations. An effective damping system can result in higher levels of comfort and safety, and can also lead to considerable savings in the total cost of a building.

With this in mind, dampers are installed in cut-outs at the lower levels of a shear wall in the present research project. This has the effect of reducing the stiffness at the base of the structure, increasing the natural period and so reducing the amount of seismic energy that will be attracted. Three types of damping mechanisms, viz, viscoelastic, friction, and hybrid friction-viscoelastic dampers are investigated. Finite element methods have been employed in the analysis using the program ABAQUS version 5.8 is used. A direct integration dynamic analysis is carried out to obtain the damped and undamped responses of the structure in terms of accelerations and deflections at all floor levels in order to evaluate the effectiveness of the damping system in mitigating the seismic response.

The damping mechanisms have been modelled as (i) a linear spring and dash-pot in parallel for the viscoelastic damper, (ii) a contact pair with friction parameter for a friction damper and (iii) a hybrid damper consisting of both a viscoelastic and a friction damper model. The earthquake events used in this study have been applied as acceleration time-histories at the base of the structure in the horizontal plane. Concrete material properties were chosen to represent the model as many high-rise buildings are constructed by using reinforced concrete.

The hypothesis regarding the placement of dampers into cut outs of shear wall suggests that by inserting the dampers into lower levels, it is possible to reduce the acceleration and deflection response of the structure. Dampers placed in the upper levels have been considered to have only little to no effect on structural response. Initial findings from this study have revealed some unexpected results. In reduction of maximum acceleration the best performance has been achieved, in nearly all cases, where dampers are placed in the lower parts of the models, which fully confirmed the hypothesis. However, with regard to the reduction of maximum displacement the best performances have been achieved by dampers inserted in upper level, while dampers inserted in lower parts have been considerably less effective. Analysis of various building models is being carried out at present to establish the effectiveness of the dampers and their optimal placement. The final outcome will be to determine a technique for optimum performance of the structure under earthquake loading.

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