Evaluation of Deflection and Displacement Amplification Factor in Steel Concentrically Braced Frames (CBF) and Steel Ordinary Moment Resisting Frames (OMRF)

It is well known that during strong ground motions most of structural damages and collapses are due to excessive displacement of stories, and other structural and non-structural elements. Therefore one of the most important objectives in seismic design procedure is estimating the maximum inelastic (actual) displacement and drift of structures occurring in severe ground motions. Seismic design provisions estimate the maximum inelastic story drifts and displacements occurring in major earthquakes by amplifying the drifts and displacements computed from elastic analysis at the prescribed design seismic force level using a deflection amplification factor. This parameter is useful for estimating minimum allowable space between two adjacent buildings, controlling story drift limitations and so on. In this research, the deflection amplification factor for both displacement and drift of four steel concentrically braced frames (CBF) and also four steel ordinary moment resisting frames (OMRF) are studied and evaluated. For each system, 2, 4, 6, and 8-story steel building are considered. These frames are subjected to 7 selected records of ground motions having different characteristic such as frequency content, peak ground acceleration (PGA), and so on. It is concluded that the deflection amplification factor for the systems under consideration is considerably higher than that recommended by Standard No.2800 Iran code. From the results of this research, a factor for both deflection and displacement amplification factor of each system under consideration is separately suggested.