INFLUENCE OF P-Δ EFFECT ON DEFORMATION RESPONSES OF FRAMES SUBJECTED TO EARTHQUAKES

The influence of P-Delta effect on structural performance of lumped mass models subjected to earthquakes was discussed. While the stability factor theta (the ratio of the equivalent stiffness to the elastic stiffness of structures) is a general parameter which expresses P-Delta effect, it had been made clear that the stability ratio tau which conveys the information of the critical deformation responses is more appropriate than theta as a parameter to express P-Delta effect. tau is the ratio of the actual theta to theta in case when structures collapse just at the end of earthquake if the plastic energy consumption is one-sided. Numerical analyses of earthquake responses of lumped mass models were performed parametrically and the results are summarized as follows; a)Increase of damage of a structure by P-Delta effect can be expressed in terms of tau. b)The maximum plastic deformation of a structure under the influence of P-Delta effect can be expressed in terms of tau. Empirical formula for average deformation response were presented. d)As a value corresponds to the collapse of frames, the critical stability ratio was presented.