Analytical investigation of elastic period of infilled RC MRF buildings

Fundamental period of vibration, dependent on mass and stiffness structure characteristics, is a key parameter in assessing seismic demand. The period can be evaluated both by means of empirical formulas and modal analysis carried out on a structure numerical model. The presence of external or internal infill elements, usually considered as “non-structural” elements, is generally not taken into account in structural modelling, although these elements can significantly increase the lateral stiffness of a Reinforced Concrete (RC) Moment Resisting Frame (MRF) building leading to a modification in dynamic properties. In this study, results of modal analyses carried out on 3D numerical RC MRF building models are presented, varying structure morphology (height, surface area, ratio between plan dimensions) and infill characteristics. Simplified formulas based on regression analysis of obtained numerical data are presented and discussed. These relationships are also compared with similar literature numerical expressions and empirical data from experimental measurements on existing buildings.