ON THE CORRELATION BETWEEN ENERGY AND DISPLACEMENT

The analysis of the seismic response of structures observed during recent earthquakes and the attempts at predicting collapse and damage level has led to the formulation of new methodologies, that take into account the actual damage potential of the ground motion and the structural behaviour. As structural damage during an earthquake ground motion may be due to excessive deformations or to the cumulative cyclic damage, reliable methods for estimating energy and displacement demands on structures are needed. Aim of this paper is the characterization of the seismic demand on multi-story framed structures by means of appropriate parameters formulated in terms of energy and displacement. The need of taking into account the local seismic demands has led to the adoption of a simplified shear-type model, capable of providing concise results of the seismic response of different structural systems subjected to a large number of strong motion records. The proposed methodology allows to take all the vibration modes that implicitly contribute to the seismic response into account, and to describe completely the distribution of displacement and energy dissipation along the height of the structure. Twenty different reinforced concrete, two bay-frames were studied as representative of various typologies of current buildings. A stiffness-degrading hysteretic model was used to represent the cyclic behavior of the frames in each story. The effect of the stiffness distribution patterns along the height of the structures and the hysteresis models describing the cyclic behavior of the systems was evaluated. Results indicate that is possible to extend the characterization of the relationships between energy and displacement from SDOF systems to MDOF systems. Moreover, the correlation between energy and inter-story drift demands appears stronger than the analogous one between energy and top displacement.