Experimental investigation of mechanical behavior of lightweight RC elements under repeated loadings

Abstract

Today, the use of lightweight structural concrete in earthquake-prone countries of the world has grown more and more. Therefore, it is important to study the behavior of this type of concrete against seismic loads. So far, many studies have been conducted on the behavior of reinforced concrete (RC) elements against cyclic loads caused by earthquakes, but recent observations show that many earthquakes occur consecutively. That is, structural elements and systems may experience several weak earthquakes or aftershocks during their lifetime. It is obvious that a structure that experiences several cyclic vibrations will suffer a degradation of strength and stiffness, and its behavior will change against subsequent earthquakes. The existing structural models consider the cyclic degradation resulting from the cyclic movement during an earthquake, but many of these models do not consider the effects of degradation caused by previous earthquakes; While this degradation can have significant effects on the behavior of structural elements. In this research, the degradation caused by cyclic loading in lightweight concrete structural elements was investigated first, and then their post-degradation behavior under different levels of degradation was studied; For this purpose, 12 specimens of lightweight RC beams and 4 specimens of lightweight RC columns were made with a scale of 50% and subjected to different uniform and cyclic loadings, and three levels of slight, moderate and extensive degradation were defined based on a number of constant fatigue cycles. Then, in the next step, the cyclic behavior of the specimens after degradation was tested in three levels of slight, moderate and extensive degradation. The results of the tests showed that with the increase in the degradation level, the amount of energy absorption of RC beams decreases; Especially in beams with extensive degradation level, the amount of beam energy absorption decreases by more than 40%. Comparing the cyclic behavior after the degradation of the damaged columns with the behavior of the intact specimen shows that the increase in the level of degradation reduces the ductility of the columns.