Effect of Vertical Component of Earthquake on the Behavior of Rubber Isolated Steel Buildings (Technical Note)

The object of this paper is to investigate the effects of vertical component of the ground motion on the behavior of isolated steel Buildings. For this purpose, a four-story building with different eccentricities is modeled. Three elastomeric isolators with different vibration periods and damping ratios as well as three different records are used to compare the behavior of the structure under the action of three and two components of the ground motion. In comparison with other works the forces of elements and influential parameters such as local uplift of isolator units has been investigated. The results show the considerable effect of the vertical component on axial forces (about 2 times) and local uplift of the columns. Also, the ratio of the vertical peak ground acceleration to the horizontal peak ground acceleration is found to be another influential parameter. Besides, the results show the deficiency of the international codes such as IBC or NEHRP in not considering the importance of the vertical component of the ground motion on the isolated structures as it has been already considered for the non-isolated ones. Because, it causes a fault in calculating the axial force of columns up to 2 times in motions with strong vertical component and about 5 percent in moderate ones.