Field Evaluation of Fundamental Period of Damaged and Retrofitted Reinforced Concrete Buildings: Case Study of Sarpol-e Zahab Earthquake

Fundamental period of a building plays a vital role in determining structural behavior during vibrations such as earthquake and estimation of building base shear in designing new structures or target displacement in the evaluation of existing buildings. Thus, having an appropriate estimation of fundamental period of buildings can have a considerable effect on design and evaluation results. As a result, after the November 2017 earthquake of Sarpol-e Zahab, ambient vibration tests were conducted on 22 reinforced concrete (RC) buildings to determine fundamental period. The obtained values for fundamental periods were compared with calculated values of proposed empirical relations by the first and fourth edition of Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800) and the first revision of Instruction for Seismic Rehabilitation of Existing Buildings (No. 360). The obtained results for damaged RC buildings with moment resisting frame show a significant difference between fundamental periods calculated by ambient vibration tests and empirical relations in such a way that in a building with a damage state 4, the obtained period from ambient vibration tests were 2.32 times of calculated value using empirical relations. Furthermore, in retrofitted RC buildings, fundamental periods calculated by empirical relations were up to 1.7 times greater than values determined using ambient vibrations. Therefore, two empirical relations for determining fundamental periods of damaged RC buildings with moment resisting frames and retrofitted RC buildings by adding shear walls are proposed by fitting curves on the obtained results of ambient vibration tests.