The effect of air cavities on the mechanisms of cracking and performance levels of side joints concrete frames

The presence of holes in the sensitive areas of the beam-to-column connection can cause unwanted damage. In this article, using the connection truss model and time history loading, the effect of the mentioned holes in changing the functional levels of the connection has been investigated. Validation was done by modeling and numerical analysis of a healthy lateral connection whose cyclic test results are available up to the collapse threshold. Four functional levels were defined based on the crack width and the effect of the presence of the cavity on the change of the crack width in the connection was investigated. It was found that due to the creation of an air cavity, the bearing capacity of the connection is reduced and it enters the failure range earlier, but the presence of the cavity can change the way of damage distribution in the connection so that some cracks are more open and others are closed. Also, the sliding of rebars increases due to the presence of holes in compression cycles, these changes increase the need for connection ductility. So that in the recent study, this slip shows an increase of up to 91%. By dividing the connection into 40 equal parts and placing the hole in different parts, the holes created at the joint of beam and column can be more destructive. On the other hand, the sensitivity is less than the central cavities. Also, the holes placed in the vicinity of the longitudinal bars, even with a small volume, can accelerate the destruction of the connection due to the intensification of the slip. It was found that the presence of a cavity can increase energy consumption, so that a cavity with a volume of 2.5% near the column can improve the average amount of energy loss by 1.6%.