NEW APPROACH FOR THE OPTIMAL YIELD-FORCE COEFFICIENT DISTRIBUTION IN THE SEISMIC DESIGN OF BUILDINGS

One of the main objectives in seismic design of buildings is to prevent the damage concentration in certain stories. As shown by past earthquakes the damage concentration leads to severe damage and even collapse of the structure, especially for near field ground motions. Energy-based design methods address explicitly the tendency of a given story to concentrate damage, and evaluate it through a parameter that measures the deviation of the actual lateral strength of the story with respect to an optimum (yet ideal) value that would make the plastic strain energy, normalized by the yield strength and yield displacement of the story, approximately equal in all stories. The objective of this methodology is to obtain the optimum lateral strength distribution expressed in terms of yield-shear force coefficient. The yield-shear force coefficient is defined as the ratio between the i-th story yield-shear force and the total upward weight born by the story. The optimal yield-force coefficient distribution is defined as one that makes the normalized plastic strain energy equal in all stories, thus preventing damage concentration in a given story. This paper proposes a new procedure to estimate for a given building and exciting ground motion the optimal yield-force coefficient distribution. The optimal distribution is estimated by means of the Pattern Search Method by iteratively changing the shear strength distribution until a uniform normalized distribution of damage is obtained. A comparison is carried out between the seismic behaviour of two case study structures designed using the proposed procedure and alternative proposals taken from the literature. The response is estimated in terms of distribution of damage and inelastic deformation