Evaluating Performance of Concrete Special Moment Resisting Frames with Different Seismic Coefficients Using Endurance Time Method

Abstract

This performance-based study was conducted to investigate the effects of seismic coefficients on performance of concrete special moment frames of 5,7, and 10-storey buildings located in Tehran, Iran. The structures are designed three-dimensionally by ETABS 2016 software according to ACI-318-08. Fifteen specimens were designed with different base shears having seismic coefficients of 0.7, 0.85, 1, 1.15, and 1.30 times the proposed value of Iranian Standard 2800, (i.e. decreased by 70 and 85%, and increased by 115 and 130%). Endurance time method (ETA20in series of ET acceleration function) as well as three real earthquake records was employed to evaluate the seismic performance of the modeled structures. The performance of structures was compared by the time of the first plastic hinges formation in beams and columns, the time of entering to nonlinear region and the time of experiencing storey drift of 2% corresponding to the life safety performance level. It was observed that the results of ET records and real records were similar to each other. A procedure was proposed for finding optimum structure with lower weight using ET method through defining efficient ratio (ER) and cost ratio (CR). Based on the results of ER/CR ratio and considering the importance of collapse prevention performance level, optimum structure was a 7-storey structure with lower weight or cost whose seismic coefficient had been reduced by 70%. It was concluded that high safety can not be achieved simply by increasing the seismic coefficient of structures.

The application of seismic parameters conversion among different structure design codes

“…In ASCE7-16 [3]: To determine the seismic risk category of buildings, such as A, B, C, D, E, F, 6 types, structure engineer will confirm them from classification of building function (I, II, III, IV) and design ground motion parameters (𝑆 or 𝑆 ), Class 'A' structures require the basic seismic measures; Class B and C require general seismic measures, generally only need to analyze the seismic loads based on the static method-Equivalent Lateral Force (ELF), and the demand of structural ductility (𝑅) requirements lower than other type; Classes D, E and F are required to satisfy the requirements of seismic measures strictly, in the meantime, it is mandatory to complete the time history analysis (Modal Response Spectral Analysis, MRSA, etc.) and the base shear forces from MRSA are not less than 85 % of the ELF results, also mean that the structural ductility (𝑅) requirements are higher than others relatively, 𝑅 is critical index for dissipating energy as well, which are illustrated by 'hysteresis curves' generally, such as Elastic type, Kinematic type [7], Takeda type [8], BRB hardening type [9], etc.…”