Correlation between Seismic Parameters of far and Near Fault Ground Motion and Response of Moment Resisting Steel Frames

In seismic countries, with regard to the damages and losses caused by ground motion, the earthquake resistant design of structures is a critical matter. Previous earthquakes have shown that the regulation in seismic codes does not guarantee the buildings to resist against seismic forces and may cause severe damage in the structures. This subject goes back to the design philosophy in seismic code and also weakness in the hypothesis of seismic design of structures. Noted that, the earthquake records include many inherent parameters affected the response of the structures. Meanwhile the seismic codes use only a few of them in the designing process such as spectral acceleration at the first mode period, i.e., Sa(T1) and well-known parameter PGA. In recent decades, many studies focus on the correlation between seismic parameters and the response of structures and found out that the used parameters in the codes do not have the best correlation with the response of structures. This finding depends on the databank of the records including the site-to-fault distance intensity of the earthquake, frequency content etc. as well as the type of earthquake resistant structure. This paper deals with a comprehensive study on the correlation between both far-field and near-field earthquake parameters and response of moment resisting steel frames. For this purpose, a series of nonlinear time history analyses were carried out on 3, 6, 9, 12, 15 and 20 moment resisting steel frame using OpenSEES. 107 records pair included 100 far-field records and 114 near-field records were selected from FEMA P695 as well as Pacific Earthquake Engineering Research (PEER) databases. 26 seismic parameters were extracted from these records, i.e. 5564 earthquake parameters were considered. Two damage indices including maximum inter-story drift (MISD) and the amount of absorbed energy were calculated in studied frames. To assess the relationship between seismic parameters and structural damage Pearson correlation coefficient was determined. The results show that Corvoda, Sa(T1), PGV, velocity spectral intensity (VSI), Housner intensity have the best correlation with response of structure in MISD and structure absorb energy in both far-field and near-field earthquakes. Also, the correlation coefficient of displacement dependent parameters is enhanced by increasing the number of stories. Moreover, the results indicate a weak correlation between PGA and response of structures for both MISD and absorbed energy as reported by previous researches. It should be noted that due to the rich frequency content of near-field earthquakes, the correlation of their parameters with seismic response of the studied frames was sensitive to the frames height. Noted that the short period structures (short height) are named acceleration sensitive and the medium and high rise building are recognized as velocity and displacement sensitive, respectively. Therefore, because of rich frequency content of near-field earthquakes, the correlation between acceleration based parameters such as PGA and displacement response of the structures are reduced by increasing the frame height. In a contrary manner, the correlation between damage indices of the structures with displacement based parameters is increased by increasing the frame height. Meanwhile, the correlation between damage indices of the structures with velocity based parameters such as PGV is the most for mid-rise structures. According to the result it can be concluded that the parameters depended on velocity like Housner intensity and velocity spectral intensity have the best correlation with MISD and absorbed energy. Also, the parameters depended on earthquake duration like Significant Duration and Effective Duration have weak correlation with the response of structures. It is shown that one cannot expect the longer duration earthquake result in more damage i.e. maximum story drift in structures.