STRUCTURE AND STEEL
Year:2006 | Volume:1 | Issue:1|Papers Count:4

Current seismic codes assume a triangular distribution of base shear for isolated buildings similar to their fixed base counterparts. In this paper the validity of such distribution is investigated for isolated structures having electrometric isolators. So different models of isolation systems are selected that cover a wide range of electrometric isolators with low to high stiffness and damping. The results of non-linear time-history analysis on these models show some conservatism in code-specified distribution compared with the observed distribution of story forces. Also a new formula is proposed instead of the triangular distribution to make a better estimation of real behavior of seismic isolated buildings.

This paper proposes a new geometry for the moment connection between I-beams and double-I built-up columns. The beam flanges are usually connected directly to the column cover plate by T-joint full penetration groove weld. The column cover plate will be quite flexible. The groove weld will also become a weak point and lead the connection to premature failure. We have studied the possibility of using full-depth side plates to modify the connection geometry. This new geometry eliminates brittle behavior and all other uncertainties that are intrinsic with the use of complete penetration groove weld. Using the side plates also eliminates all uncertainties about the deformation and buckling of double-I column cover plate. A series of five non-linear, three dimensional finite element models were developed to study the behavior of moment connection of I-beams to double-I built-up column under cyclic loadings. The results obtained from our numerical analysis indicate that this new connection geometry has sufficient strength and ductility to be classified as a SMF connection.

In this paper, parametric seismic performance evaluation of tall steel moment resisting frames with shear walls is presented. The performance point of each frame is determined by principals of capacity and demand curves. The evaluated frames are of 15, 20 and 25 storey. Effective damping of each frame is calculated using ATC-40 method. Effect of parameters such as shear to wall stiffness ratio, total structure stiffness to frame stiffness ratio, wall width to structure height, number and width of bays, and height of the frames to seismic performance are considered and results are evaluated for immediate occupancy performance level.

In this paper a new type of earthquake energy dissipation element has been introduced. The element is supposed to be used as a supplementary element in concentrically braced frames to improve the ductility of the whole system. Such elements usually yield before critically (instability) load of the braced systems. Using this approach, during a strong earthquake cause only this element yields and other frame elements (beams, columns, braces, connections) should be remain in the elastic range of behaviors. The current studies have theoretically and experimentally investigated the application of this special link element. The importance of such mechanism is the ability of this device in dissipation of the input earthquake energy by using torsional behaviors. This member could be used as a fuse element in seismic design and rehabilitation of the concentrically braced frames.