Experimental evaluation of damage effect on dynamic characteristics of concrete encased composite column-beam connections

摘要

A major defect in determining the structural response for concrete encased composite columns using finite element is due to the uncertainties and assumption associated with the modeling process. Therefore, experimental measurements should be performed in order to validate the numerical results as well as obtain the real structural response. This paper seeks to address an experimental study about the evaluation of damage effect on the dynamic vibration characteristics of concrete encased composite columns (CECC) considering different column-beam connection types using ambient vibration tests. In an attempt to do so, four half scale concrete encased composite column-steel beam were built and tested in the laboratory with different column-beam connection types abbreviated as CECC-A, CECC-B, CECC-C and CECC-D without any changes in geometrical configuration of specimens and test setup. Cyclic loading tests were conducted in order to assess the post damage condition, while ambient vibration test were performed to extract the experimental dynamic characteristics such as natural frequencies, mode shapes and damping ratios using Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) methods for both undamaged (intact) and damaged conditions. The natural frequencies have decreased distinctly and mode shapes were broken with damages. These tests revealed that ambient vibration tests are enough to identify the dynamic characteristics of engineering structures for different conditions. The maximum differences in natural frequencies were calculated between 21.72% and 39.96%. A good agreement was noted for undamaged condition, the mode shapes were identical and the Modal Assurance Criterion (MAC) had value of 1.0. In contrast, there was not a good agreement for post damage condition. The mode shapes were different and MAC values were close to zero. Lastly, as the experimental damping ratios were examined, the results supported the idea that there were some differences and the values did not correlate favorably. These results are the compatible with the literature, but it is thought that the differences typically indicate that higher excitation levels are required to accurately capture the damping ratios.