Comparing Versions 3 and 4 of Standard 2800, in Improving Seismic Behavior of Intermediate Moment Frame Buildings

Nowadays, performance evaluation of buildings against earthquakes is one of the common debates among researchers. Old buildings designed on the basis of previous versions of seismic codes are exposed to more damages in earthquakes. To evaluate vulnerability of existing buildings for earthquakes, Instruction on Rapid Earthquake Evaluation of the Existing Buildings (Code No. 364) has been proposed. By this code, a building can be rapidly evaluated by easily available data such as structural type, designing and construction date, appearance, etc., with very low cost. One of important parameters for such evaluation is the version of the seismic code (Standard 2800) which had been applied in the designing process of inspected building; later version has greater score.  However, the rapid evaluation code (Code No. 364) has been prepared before releasing version 4 of Standard-2800 and therefore do not have the score of designing with this version. Therefore, this paper is focused on comparing version-3 and vetsion-4 of Standard 2800 in designing buildings. For this, three buildings, having 3, 5 or 7 story, with regular plane is considered. Each is designed twice, based on the version-3 and vetsion-4  and then their fragility curves are calculated. The obtained fragility curves are compared in two levels of earthquakes having return period of 475 years and 2475 years (PGA of these earthquakes are assumed as 0.35g and 0.5g, respectively). To achieve the fragility curves, 50 earthquake records, recommended by FEMA-P695, are considered. They include 22 far field ones, 14 near field ones having pulse and 14 near field records without pulse. To consider nonlinear behavior of the structural elements, concentrated plasticity is assumed at two ends of each element by Opensees software. Properties of the plastic hinges are introduced in the software based on Lignos model. The obtained results show that in IO performance level, there is no meaningful difference between the structures designed on the basis of version 3 and version 4 of Standard-2800. However, in Life Safety (LS) and Collapse Prevention (CP) performance levels, version 4 leads to much better structure. Furthermore, the difference between these two versions of standard is greater for 475 year earthquakes, in comparison with 2475 year earthquakes, and also for LS rather than CP performance level.