Damage effect on experimental modal parameters of haunch strengthened concrete-encased composite column–beam connections

This paper presents an experimental study about the effects of damage on modal parameters of haunch strengthened composite column–steel beam connections. Five specimens having various composite column and steel beam connection details were constructed in order to be examined in laboratory condition. Non-destructive experimental measurements were conducted to extract the modal parameters using frequency and time domain methods before and after damage conditions. Quasi-static cyclic tests were performed to assess the damaged conditions in connection zones of the test specimens. At the end of the study, it is observed distinctly that there is a decreasing trend in natural frequencies with damages. Also, no compliance is observed between mode shapes pre- and post-cycling loading tests. The biggest dissimilarities concerning natural frequencies were determined among 26.57% and 36.54%. The value for modal assurance criterion was 1.0 for undamaged condition. However, in post-damaged situation, the mode shapes have changed and modal assurance criterion values nearly approached zero. Finally, experimentally obtained damping ratios have been analyzed. The outcome of the study has shown some dissimilarity and that the values are not being correlated constructively. Despite the fact that the results are consistent with the available literature, it is assumed that these dissimilarities point to the fact that higher levels of excitation might be need to precisely record the damping ratios.