Experimental Free Vibration of Damaged RC Beam-Column Joints

Reinforced concrete (RC) is a relatively modern construction material and it is often damaged both with cracking due to loading or corrosion of reinforcement. The last seismic events occurred all over the world, have shown that buildings characterized by RC frames, built some decades ago before the more recent seismic rules, have suffered damages due to weak materials and lack of frame’s ductility to resist seismic actions. In particular, damages interested column/column-beam joints. From this point of view, the vibration monitoring of the structural integrity of damaged RC elements is crucial. Among the methods of integrity’s monitoring, vibration analysis is more convenient as non-destructive testing (NDT) method. In this paper, full-scale experimental testing on a frame model with RC beam-column joint, using a nondestructive method of control based on vibration tests is described. The RC frame was firstly tested under static loading to simulate seismic action. The specimen was firstly damaged and, successively, strengthened with externally bounded Basalt-FRP strips. The vibration tests took place into three stages, after the loading path on the unstrengthened model, before damage and after the loading path on the strengthened model to control the frequency variation values. Dynamic characteristics of the structure determined from the tests are presented. Moreover, the envelope of Frequency Response functions (FRFs) obtained by the dynamic experimental tests are given. Finally, discussion and comparison of results are shown.