چكيده به لاتين
Considering the high seismicity of Iran and the suitable performance of modern lateral force resisting systems, this paper investigates the seismic behavior of steel structures equipped with linked- column- frame system (LCF) under single and consecutive near- field earthquakes. In this regard, steel structures with 4, 6, and 8 story (the usual number of stories in Iran) containing dual LCF with shear performance for linked beams have been designed based on 2800 standard and implemented in Opensees software. After verification of studied models with the valid researches such as Golestani et al., (2023) – one 3 story steel frame with 2.0 m linked beam considering American sections – with comparison of periods and Push over curves, nonlinear dynamic analysis have been performed under single and consecutive near field earthquakes with and without pulse. In this study, the proposed near filed records with and without pulse by FEMA356 have been used and “back to back” or “Repeated” method has been selected to generate the successive shocks. For this purpose, first shock is considered as second shock after 30 seconds time gap with zero acceleration. It should be noted that the seismic scenarios are scaled based on 2800 standard considering the fundamental period of the studied models. The results indicate that as the number of stories increases, the structural damage and maximum displacement - especially for studied frames exposed to consecutive earthquakes without pulse - increase. In this study, for evaluation of the performance of linked beams, steel frames with 4 stories have been designed and analyzed with shear and flexure performance. The results show that the average maximum relative displacement of the roof is 4% and 3.9%, the average relative displacement damage index is 1.2% and 1.4%, respectively, for the 4-story frame containing linked beams with shear and flexure performance under successive near fault records without pulse. Similarly, in the absence of pulses in the consecutive seismic scenarios, Raphael's damage index for the above mentioned 4 story frame has been reported as 78% and 80% considering the shear and flexure linked beams. In this study, a comparison has been made between 4, 6 and 8-story frames, and the results corresponding to the maximum relative displacement of the roof are 4% for the 4-story frame, 4.3% for the 6-story frame, and 5% for the 8-story frame. In the following, the average value for relative displacement damage index is reported 1.3%, 1.4% and 1.7% for 4, 6 and 8 story frames in critical case. Generally, the caused damages by seismic sequence phenomenon are about 16% more than the single case. The average ductility damage index for the most critical mode – successive shocks without pulse – for 4, 6 and 8 story frames, is about 174%, 226% and 281%, respectively. In general, it can be claimed that seismic sequence phenomenon can increase the damage index compared to the single case because of the accumulation of damages caused by the previous earthquakes and the lack of sufficient opportunity to restore the structure to its initial equilibrium state, and the consideration of this phenomenon in the analysis and design of structures seems necessary, despite the proposed methodology in the seismic regulations.
