Investigating the pattern of plastic hinge formation in steel moment frames under near-field and far-field earthquakes

Structural health monitoring is an important issue that should be considered for the structures. In this regard, the main goal of the current research is to investigate the formation pattern of plastic hinges in steel moment frames due to near-field and far-field earthquakes. To reach the goal, after modeling three types of 3, 5 and 8-story frames with 2, 3 and 4 spans by Sep2000 using two categories of earthquake records of far-field and near-field for different levels of peak ground acceleration (PGA), the process of forming plastic hinges has been investigated and evaluated by performing nonlinear time history analysis. The obtained results showed that the first plastic hinges were formed in the 3-story frames in the lower stories and in the case of the 5 and 8-story frames in the middle stories. Also, by applying the higher PGA, the formation of hinges in the upper floors of the frames is developed. furthermore, the frequency corresponding to the formation of the first collapse prevention (CP) hinge in the case of the 3-story frame with 2, 3, and 4 span is equal to 1.11, 1.31, and 1.22 Hz, in the case of the 5-story frame it is equal to 0.85, 1.03, and 0.94 Hz, and in the case of the 8-story frame it is equal to 0.44, 0.42, and 0.4 Hz, respectively. Other results showed that the behavior of 3-story frames under the effect of far-field records and the behavior of 5 and 8-story frames under the effect of near-field records are in higher dynamic instability conditions. Also, with the increase of spans and the number of floors, the possibility of damage and dynamic instability in the frames has increased. For all frames with different story numbers, by increasing the number of spans from 2 to 4, an increase of 5.88, 22.4 and 38.3% has been obtained respectively in the number of hinges formed in the frame. Also, by increasing the height of the frame from 3 to 8 floors, the number of plastic hinges formed in 2, 3 and 4-span frames has increased by 41.4%, 74.7%, and 61.7%, respectively.