Modal testing and finite element model calibration of in-filled reinforce concrete frames

Abstract

In this study, modal testing and finite element model calibration of in-filled reinforced concrete (RC) frames are studied. For this purpose a full-scaled, one bay and one-story RC frame is produced and tested for plane and brick in-filled conditions. Dynamic characteristics, such as natural frequencies, mode shapes and damping ratios, of plane and in-filled RC frames are determined using the Operational Modal Analyses method under ambient vibration. The RC frame is vibrated by natural excitations with small-impact effects and the response signals are measured using sensitive accelerometers during ambient vibration tests. Measurements of time-frequency range and effective mode number are determined by considering similar studies and literature. To obtain experimental dynamic characteristics, enhanced frequency domain decomposition and stochastic subspace identification methods are employed. Analytical modal analysis is performed on a two-dimensional finite element model of the frames using SAP2000 software to provide analytical frequencies and mode shapes. The results of ambient vibration tests show that dynamic characteristics change significantly depending on the existence of an in-fill wall. The first five natural frequencies are obtained experimentally between 16.64 and 179.20 Hz, and 63.56 and 226.12 Hz for plane and brick in-filled, respectively. Dynamic characteristics obtained by analytical and experimental methods are compared with each other and the finite element model of the frames is updated by changing some uncertain modeling parameters, such as material properties and boundary conditions, to reduce the differences between the results. At the end of the study, maximum differences in the natural frequencies are reduced on average from 39% to 8% and a good agreement is found between analytical and experimental dynamic characteristics after finite element model updating. This result shows the importance of finite element model updating to reflect the current behavior of the structures. In addition, it is seen that material properties are more effective parameters in the finite element model updating of the plane frame. However, for the brick in-filled frame, changes in boundary conditions determine the model updating process.