;The purpose of the study is to observe the seismic behavior of reinforced concrete(RC) structures with normal and very low concrete strengths by means of the monotonic and cyclic loading tests on compressive concrete cylinders and RC simply supported beams. The results of the concrete compressive test showed that the empirical equation of the concrete elastic modulus suggested by the Taiwan’s researcher [16] is not conservative for the very low concrete strength. Meanwhile, the effect of the cyclic loading on the elastic modulus of the very low-strength concrete is much more obvious than the normal concrete, which decreases to 67% of the value calculated by the empirical equation. The stress-strain curves measured from the monotonic and the cyclic loading are repealed in a similar excursion. Also the stress-strain curve of the very low concrete strength can be conservatively described by the theoretical model proposed by Popovics [5]. In the second part of the study, four simply supported RC beams with different concrete strengths (f_c^′ respectively equals 21 MPa and 10 MPa), subjected to three-point monotonic and cyclic loading, were tested. The results showed that the stress block method proposed by ACI 318-14 [1] and Collins [3] could be used to evaluate the bending moment strength of RC beams with normal and very low concrete strength. The predicted values using these two methods are similar. These predicted values are smaller than the measured ones. That is, the stress block method can be used to evaluate the bending moment strength of RC beams with very low concrete strength. However, the maximum bending moment of the low-strength RC beam occurred at the concrete compressive strain of 0.006, which is significantly different from the strain of 0.003 measured from the normal RC beams. As for the effective moment of inertia (I_e), these values(I_e) measured from the tested beams at the yield loading stage are ranged between 0.2 to 0.3I_g, where I_gis the full sectional moment of inertia. These values represented as no different, regardless of the efficiency of monotonic or cyclic loading. It was also found that the development length equation specified in ACI 318-14 showed less conservative when the bond strength of the RC beams with very low-strength concrete was assessed.
