**1. Introduction**

Semi active magnetorheological (MR) damper have a note of attention in the use of control systems to control vibrations in structures during earthquake. There are various semi active control systems which attracted much attention now a days because it possesses the adaptability of active control system. This MR damper makes the viscosity to more apparent, operate in less current, which produce high damping force. In semi active the properties will be varied dynamically, therefore which is quite effective in structural control responses due to its wide range loading condition [1–5]. The main advantage of semi active control device is their low power requirement. Particularly, the most promising device for seismic control is MR, MR fluid is the major constituent in MR damper which results controllable damper [6–9]. The characteristics of MR fluid is when applying magnetic field, their ability to change from liquid to semi solid state with the reaction time of less than 50 milliseconds. A typical MR fluid consists of 25–55% by volume of magnetic iron particles like carbonyl iron, suspended in an appropriate carrier liquid. The diameter of the particle was found to be 3–5 μm in size [10–16]. Furthermore, MR fluid is advantageous due to its unique phase transition property in the presence of magnetic field. However, the major disadvantage faced by MR fluid is sedimentation. Commonly, commercial lubricants were added to reduce gravity settling, which additionally enhance particle suspension [16–20].

The focus of this paper is to experimentally demonstrate the ability of the MR damper to reduce structural responses. Following a description of the experimental setup, cyclic load test is carried out in the RC frame with and without damper. The effects of stress, strain, displacement and load behavior for RC element with various time interval is studied with and without MR damper. The results indicate for seismic response reduction, MR damper is quite effective for wide range.
