FREE VIBRATION TEST OF LOW STRENGTH REINFORCED CONCRETE BRIDGE COLUMNS AT SEVERAL DAMAGE STATES

The study represents the experimental test results of four scaled downed reinforced concrete bridge columns specimen subjected to free vibration testing. The specimens were made of low strength concrete having circular cross sections. The free vibration test was performed in order to evaluate the specimen’s dynamic characteristic for the undamaged and damaged conditions of different loading intensities. The dynamic characteristics of the specimens were assessed in terms of natural period of vibration and damaging ratio of the structures. The physical inertial masses during the test were simulated using the concrete blocks supported at the top of the specimen. Initially the test was conducted on the undamaged specimens for different load intensities. In order to cause damage to the specimens, quasi-static cyclic loading test was carried out. Finally, free vibration test on the damaged specimens was performed and changes in the dynamic characteristics of the specimen at various loading damage levels were examined. The test results indicate that the natural period of vibration increases and damping ratio decreases with the increase in mass supported on the top of the specimen. However the strength of concrete has no direct effect on natural period and damping of the specimens but it has effect on the level of damage of the specimen. Moreover, the natural frequency of vibration is significantly affected by the damage of the specimen. The experimental test results presented in this paper would provide valuable insight in how the damping characteristics change with changes in loading/ damage levels of reinforced concrete bridge columns.