Evaluation of Seismic Performance of an Educational Structure during August 11th 2012 Ahar-Varzaghan Earthquake

In August 11th 2012, at 16:53 and 17:04 two earthquakes with magnitudes of 6.3 and 6.4 occurred in East-Azerbaijan province, North-West Iran. The epicenter of the event was located about 10 km south of Varzaghan city. The peak ground acceleration for the first and second events were recorded as 427 and 532 cm/sec2, respectively. The Responsible author had the opportunity to visit the area, immediately after the events as a member of IIEES reconnaissance team. The villages around Ahar and Varzaghan as well as both cities suffered severe damage. Light structural damage was observed in transportation structures while a severe damage occurred in the buildings. The office buildings and educational facilities were among the damaged structures. The Azad Islamic University of Varzaghan is a 4 storey building with steel structure. The facility is located at the south of the City. The structure is equipped by bracings and moment frames as lateral bearing system. The field observation revealed the severe damage to non-structural components of the building. Cracks occurred in infill walls. Toppling and falling of equipment and objects was observed in different floors. Damage to ceilings was observed in all levels of the building. Both out of frame and in frame failure of masonry infill walls were observed in the building. A Numerical Study was carried out to estimate the performance of the building during the earthquake and find out the location and intensity of probable nonlinear behavior if the elements and connections.Push over analysis was performed to evaluate the behavior of the structure in extensive seismic displacement demands. Target displacement was calculated according to the FEMA 356. The analysis was performed by SAP2000, a finite-element analysis software, which is capable of modeling nonlinearbehavior of structural frames through concentrated hinge models. The analysis resulted in estimation of sequential nonlinear behavior of the building and sequence of appearance of plastic hinges in the frame elements. The strong motions of both events were recorded by the Iran Strong Motion Network. They could make the time history analysis of the structure possible. Time history of acceleration and displacement of the building in different floors were calculated. The analysis could reveal that although the floors of the building experienced considerable acceleration during the strong motion, the relative displacement of the building was limited. The calculated floor relative displacement values are smaller than the '0.025Ífloor height' as the code criteria. This could result in a limited response of the structural elements and prohibit the occurrence of nonlinear behavior and seismic structural damage to the building.