Evaluation of damage indices for RC beams under cyclic loading - A simple technique

摘要

Applicability of damage indices for concrete is limited due to the limited calibration of the indices against observed damage in laboratory tests or earthquake investigations. Various experiments over the years indicated no obvious shear dependent trends on cyclic combined shear and flexure in the evaluation of damage index1. Here an attempt was made to find a simple and realistic indicator, which gives a reliable measure of the structural damage, and make use of this indicator in the design stage calculations of medium and long period structures. Most of the indices show a high level of scatter depending on the mode of failure. Monotonic and cyclic tests were conducted on normal, and latex modified fibre reinforced concrete beams. Two available models for damage indices in the literature, namely, Park and Ang model~2 and the model suggested by Rao et al ~3, were used to predict the damage indices. A simple set of relationships connecting damage index to the failure cyclic ductility ratio, shear span to depth ratio and cyclic amplitude have been derived. The above relationships have been validated on the test data generated during the present investigation and also on the data available in the literature. A procedure to evaluate the demand-monotonic ductilit} ratio at failure corresponding to a given state of damage and the shear span to depth ratio has been developed. The beam can then be suitably designed and detailed to meet the above requirements.