All structures respond to dynamic effects by vibrating. The mode shape, frequency and damping ratio of the vibration constitute the dynamic parameters or modal behaviour characteristics of the structure. Theoretical and experimental modal analysis are used to calculate and determine dynamic parameters. Experimental modal analysis provide more accurate results than the results provided by theoretical modal analysis; since they use the current state of the structure. Operational Modal Analysis (OMA), one of the experimental modal analysis types, is based on the principle of measuring the response of the structure to ambient vibrations and obtaining modal behaviour parameters (mode shape, period, damping ratio) by processing this data. Ambient vibrations created by environmental factors (traffic, daily activities, etc.) have very low amplitudes. For this reason, ultra-high sensitive sensors are used to measure the response of the structure to these vibrations by means of displacement, velocity and accelerations.
In this study, the effect of infill walls on the dynamic parameters of a five-storey reinforced concrete building was studied by operational modal analysis. Infill walls are not considered as structural elements in the design of reinforced concrete structures and their effect on structural rigidity is ignored. However, studies have shown that; infill walls well connected to columns and beams significantly contribute to lateral stiffness; hence natural vibration period of the building. Ignorance of the contribution of infill walls to the period of the structure may result in intolerable errors of seismic design load calculations.
Within this context; a 5-storey reinforced concrete residential building was studied. Finite element model of the structure created in SAP2000 software for theoretical modal analysis. Experimental modal behaviour parameters of the structure were obtained by operational modal analysis. By comparing the theoretical and experimental dynamic parameters, the effect of the infill walls on the dynamic parameters of the building was studied.
Theoretical modal analysis on the finite element model without infill walls resulted in identical mod shapes with that of operational modal analysis and varying modal frequencies for corresponding mod shapes. However, finite element model calibration by inclusion of infill walls represented by diagonal struts resulted in more corresponding modal frequencies and identical mod shapes with that of operational modal analysis.