Proposal of a damage index for the prediction of failure of short links

Abstract

Recent approaches for the assessment of the seismic performance of buildings are usually based on the evaluation of the mean annual frequency of exceedance of assigned limit states. Hence, the probabilistic formulation of damage of structural elements is of utmost importance. In this paper, a damage index is proposed to predict failure of short links made of European cross-sections and endowed with web stiffeners designed in keeping with the requirements of Eurocode 8. As the rotation capacity of short links strongly depends on the loading history, the proposed damage index is based on the cumulative damage concept and formulated using the Coffin-Mason model and Miner’s rule. To calibrate the damage index expression, a refined finite element model of the link has been first developed and validated by comparison with results of laboratory tests available in the literature. Then, the model has been used to simulate the response of short links subjected to cycles at a constant value of the total link rotation angle and to evaluate the number of half cycles to failure. This number is scarcely influenced by the size of the cross-section while it depends on the mechanical length of the links. The accuracy of the proposed damage index has been proved by means of cyclic loading protocols or displacement loading histories characterized by randomly generated values of the link rotation angle. Finally, a probabilistic analysis has been carried out to model and estimate the residuals of the damage capacity so that Monte Carlo analyses with uncertain damage capacity may be performed. Results indicate that the logarithms of the residuals are normally distributed with a null mean value and a standard deviation equal to 0.0525.