Abstract
A structure may be subject to several aftershocks after a mainshock. In many seismic design provisions, the effect of the seismic sequences is either not directly considered or has been underestimated. This study examined the seismic behavior of reinforced concrete (RC) moment-resisting structures with concrete shear walls under seismic sequences. Two three-dimensional structures of short and medium height were designed and analyzed under seven real mainshock–aftershock seismic sequences. The models were loaded and designed according to the Iranian seismic code (4th ed.; Standard No. 2800) and ACI-318. The structures were analyzed using the nonlinear explicit finite element method. The maximum displacement, inter-story drift ratio, residual displacement, and ratio of aftershock PGA to mainshock PGA were investigated and assessed. Because of the high lateral stiffness of the shear walls in addition to their completely elastic behavior, the aftershocks did not increase the inter-story drift ratio or relative displacement in the short structure model. The medium height model under the seismic sequences showed a significant growth in the relative displacement (roughly 25% in some cases), inter-story drift ratio, plastic strain, and residual displacement (42.22% growth on average) compared to the structure that was only subjected to the mainshock. Remarkably, in some cases, the aftershock doubled the residual displacement. Unlike the moment-resisting frames under seismic sequences, the models showed no significant growth in the drift ratio with an increase in height. Assessments indicated that the ratio of aftershock PGA to mainshock PGA is a determinative parameter for structural behavior under seismic sequences, such that high values of this ratio (> 0.6) caused significant increases in the residual and relative displacements.
Highlights
An earthquake in seismic zones is not a single event and in most cases a chain of ground motions with different magnitudes accompanies it
This paper studies the seismic behavior of RC moment-resisting structures with concrete shear wall under seismic sequences
The Friuli aftershock causes no growth in drift ratio, residual, and relative displacement, the reason for this behavior could be a low ratio of aftershock acceleration to mainshock acceleration (0.3)
Summary
An earthquake in seismic zones is not a single event and in most cases a chain of ground motions with different magnitudes accompanies it. Multiple earthquakes occur around the world, especially in regions with complex fault systems These fault systems usually do not release all the accumulated strain energy during the first vibration or mainshock; tensions and strains are formed in different locations of the fault system and lead to consecutive vibrations or aftershocks. Michoacán earthquake (Mexico City, 1985) with respectively the mainshock and aftershock of 8 and 6.6 Richter and Northridge earthquake (Los Angeles, 1994) with a magnitude of 6.7 Richter followed by a 6 Richter aftershock are good examples of this complicated event (Amadio et al, 2003) Despite their devastative structural effect, in most of the analytical studies and design codes, the effect of aftershocks has been neglected, underestimated, or has not been considered directly
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
