A uniaxial cyclic model for confined and unconfined concrete is developed. Starting from an existing model, the cyclic rules to define inelastic strain and degradation of strength and stiffness are first reviewed and then modified to produce a new concrete model with enhanced performance. Comparisons at the stress-strain level between the new and existing concrete models reveal the adequacy of the new model in terms of numerical stability and increasing degradation of strength and stiffness under increasing cyclic strain. The proposed model is validated by comparing analytical predictions with experimental results of RC members under cyclic and dynamic loading. Good agreement is observed between analysis and experiments, confirming the ability of the model to predict the cyclic and dynamic behaviour of RC members with mixed axial-flexural response characteristics
A review of the evolution of energy dissipation devices of hysteretic type is presented. Both friction and yielding devices are included in the paper covering a worldwide range of applications. Due to the increasingly large number of available devices, the paper does not attempt to present a state-of-the-art on the subject, but to focus on discussing the main original research efforts that have paved the way of the current technology of energy dissipation devices. Relevant past applications of devices are briefly described making particular emphasis on important issues such as experimental assessment, effectiveness of their modeling by nonlinear analysis techniques, materials and constructability. Devices selected for discussion in the paper are presented in a historical perspective and are considered pioneer original steps or research efforts directed towards an efficient and rational use of energy dissipation technology.
A parametric study on the scaling of natural accelerograms using spectrum intensity scales is presented. A series of nonlinear time-history analyses for a SDOF system is conducted using an ensemble of world-wide damaging earthquake records for a wide range of seismic conditions. Structural parameters considered in the study include: yield seismic coefficient, yield natural period and postyield stiffness. The effectiveness of several spectrum intensity scales is evaluated in terms of their correlation with displacement ductility demand. Results indicate that there is not a unique scale with best performance over the entire range of strength and stiffness. An alternative combined criterion to define spectrum intensity is proposed in terms of a system of spectrum intensity scales. The system optimises the correlation between spectrum intensity and displacement ductility demand. This is achieved by defining regions in the space of structural parameters for which it is possible to identify a spectrum intensity scale of best performance.
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