Investigations of elastic vibration periods of reinforced concrete moment-resisting frame systems with various infill walls

The fundamental period of vibration is a crucial characteristic in assessing the dynamic performance of reinforced concrete (RC) buildings because it is not only directly related to the mass and stiffness of the structure, but also to the lateral actions applied, e.g. earthquakes and winds. In this study, the RC moment-resisting frame (MRF) systems designed under gravity and wind loading have been evaluated by utilising 3D FE modelling incorporating eigen-analysis to obtain the elastic periods of vibration. The parameters considered include the number of storeys, the number and length of bays, plan configurations, mechanical properties of infill walls, and the presence of openings in the uncracked and cracked infill walls. These analyses provide a sound basis for further investigating the effects of these parameters and exploring the possibility of proposing new formulas for predicting the fundamental vibration period by utilising regression analyses on the obtained results. The proposed numerically based formula for vibration periods of bare RC frame models reasonably agrees with some cited formulas for vibration period from design codes and standards due to disregarding contributions of infills' stiffness towards the structural systems. Meanwhile, the proposed formulas for RC MRF buildings with uncracked infills agree well with most cited experimentally based formulas and some numerically based ones. However, the proposed formulas for RC MRF buildings with cracked infills only reasonably agree with some cited numerically based formulas.