Evaluation of Ductility of Rinforced Concrete Structures

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1. A series of equations to evaluate the ductility of reinforced concrete members were derived based on static cyclic loading tests on small scale specimens of a cantilever type. Valuables contained in these equations are main reinforcement ratio, web reinforcement ratio, shear span ratio, axial compressive stress, compressive strength of concrete, maximum size of coarse aggregate, number of repetition of loading. In these equations, the influence of the reinforcements arranged along side faces on the ductility is taken into consideration by counting the amount arranged below the neutral axis as main reinforcement. It was proved by the comparison of calculated ductilities with the experimental ones that the derived equations give satisfactorily accurate results, the average of the ratio of calculated value to the experimental one being 1.09 and the coefficient of variation being 14.5%.2. As the loading rate is increased, the maximum value of restoring force increases, but at the same time, it decreases more rapidly on the descending branch. It is supposed from this fact that the loading rate has some influence on the ductility. However, this influence could not be contained in the equations described above because of lack of sufficient data.3. A restoring force model was proposed, taking the ductility based on the result described in 1 into account. It was proved by comparison of the response analysis on the 2 stories rigid frames with the results of shaking table tests that the model can trace the behavior of the frames upto the ultimate state satisfactorily. Therefore, it can be concluded that the evaluation of ductility of reinforced concrete structures is possible when response analysis is carried out using the proposed model.