MIDBROKEN REINFORCED-CONCRETE SHEAR FRAMES DUE TO EARTHQUAKES - A HYSTERETIC MODEL TO QUANTIFY DAMAGE AT THE STORY LEVEL

A nonlinear hysteretic model for the response and local damage analyse s of reinforced concrete shear frames subject to earthquake excitation is proposed, and, the model is applied to analyse midbroken reinforce d concrete (RC) structures due to earthquake loads. Each storey of the shear frame is represented by a Clough and Johnston hysteretic oscill ator with degrading elastic fraction of the restoring force. The local damage is numerically quantified in the domain [0,1] using the maximu m softening damage indicators which are defined in closed form based o n the variation of the eigenfrequency of the local oscillators due to the local stiffness and strength deterioration. The proposed method of response and damage analyses is illustrated using a sample 5 storey s hear frame with a weak third storey in stiffness and/or strength subje ct to sinusoidal and simulated earthquake excitations for which the ho rizontal component of the ground motion is modeled as a stationary Gau ssian stochastic process with Kanai-Tajimi spectrum, multiplied by an envelope function. (C) 1997 Elsevier Science Limited.