Model test on scale effect of the frequency decreases of the reinforce concrete beam due to moment cracks

For the experiment on the damage identification of reinforced concrete beams, Scaled model results are often used to investigate the damage identification of in-site structures based on the dynamics. However, the variation of dynamic characteristics with the increasing damage for concrete structures is nonlinear. It is necessary to check the reasonableness that test results with small scales are extended to prototype. In the paper, in order to investigate the relationship between scale and frequency reduction of the reinforced concrete beams due to moment cracks in model test, three different sizes of reinforced concrete beams are designed and made based on elasticity similitude law. Then, step loading method with 5 level is used to gain different damage states of beams, and natural frequencies of the beams in different damage states is measured by hammering test. The experimental results show that with the increase of damage states, the frequencies of the concrete beams are reduced, while the amplitude of reduction changes nonlinearly. The trend of the frequencies reduction of the different sizes beams is the same in the same damage states, but it has nothing to do with reduced-scale. As a consequence, scaled model test can only be used for the qualitative research of the change of dynamic characteristics of the damaged reduced-scale concrete beams.