Evaluation Of Dynamic Properties For Asymmetric Linear System

Abstract

The asymmetry in the building arises due to unsymmetrical distribution of mass, sti ness, damping and strength. Asymmetric building frame is characterized by coupling between translational and torsional degrees of freedom under the in uence of an earthquake. And thus, it is susceptible not only to bending oscillations, but also torsional oscillations that can lead to failure of the building frame. If oscillations of such an asymmetric building frame are beyond acceptable limits, they need to be control by some control techniques. There are three types of Response control techniques which are widely adopted in the practice, namely, Passive damping, Active damping and Hybrid damping techniques. All techniques have distinct advantages and disadvantages and is adopted based on dynamics of the Problem. In the present study asymmetric building with planar and geometrical irregularity are considered. Asymmetric building is modelled as Single Degree of Freedom (SDOF) System with L- and T- shaped scaled model fabricated using aluminium material as well as Aluminium model with one column of mild steel. To characterize coupling between translation and torsion degrees of freedom, SDOF models are subjected to base excitation at varied angle of incident using Uniaxial Shake Table. SDOF models are instrumented with Uni-axial Accelerometers and Data Acquisition Systems to capture translational and torsional response of the test models. Mathematical formulation is developed to compare experimental and analytical results. It has been found that no signi cant in uence of angle of incident of base excitation is observed for the SDOF models with planar and material asymmetry. Existence of coupling between translational and torsional degree of freedom for Planar and Material Irregular models is established through response measurements. Air based Pneumatic Damper and Elastic and Friction based Piston Type Damper categorized as Passive Dampers are developed. Both types of Passive Dampers are characterized under displacement controlled cyclic loading and Equivalent Damping ratio () is determined at Civil Engineering Department, Institute of Technology, Nirma University. It has been observed that both passive dampers show hysteric behaviour under cyclic loading and hence capable of dissipation of energy to reduce seismic response. These passive dampers are then installed in asymmetric SDOF models and are tested under free and forced vibration. It has been observed that significant increase in damping value of SDOF models with passive dampers yields substantial reduction in the response.