Research Note» Evaluation of the Methods of Maximum Lateral Displacement Estimation of R/C Moment Structures due to Earthquake

For seismic design, it is important to estimate the, maximum lateral displacement (inelastic displacement) of the structures due to earthquakes for several reasons. Seismic design provisions estimate the maximum roof and storey drifts occurring in major earthquakes by amplifying the roof displacement and drifts of the structures obtained by elastic analysis subjected to seismic design load, with a coefficient named “displacement amplification factor” which is greater than one. Here, this coefficient depends on various parameters such as ductility factor and overstrength factor. The present research aims to evaluate the value of the displacement amplification factor in seismic design codes and then tries to propose a new value as displacement amplification factor to estimate the maximum lateral structural displacement due to severe earthquakes. In seismic codes, since the displacement amplification factor is related to “force reduction factor”, hence; this aspect has been accepted in the current study. Meanwhile, two methodologies were applied to evaluate the value of displacement amplification factor and its relation with the force reduction factor. In the first methodology, which is applied for all structures, the ratio of displacement amplification and force reduction factors was determined directly. Whereas, in the second methodology that is applicable just for the R/C moment resisting frames, the ratio was obtained by calculating both factors, separately. The results were alike and both of them could estimate the ratio of the two factors from 1 to 1.2. The results also indicated that the ratio of the displacement amplification factor and the force reduction factor differs to those proposed by seismic provisions such as NEHRP, IBC and Iranian seismic code (Standard no. 2800).