Abstract
The influence of P-Δ effect on structural performance of lumped mass models subjected to earthquakes was discussed. While the stability factor θ (the ratio of the equivalent stiffness to the elastic stiffness of structures) is a general parameter which expresses P-Δ effect, it had been made clear that the stability ratio τ which conveys the information of the critical deformation responses is more appropriate than θ as a parameter to express P-Δ effect. τ is the ratio of the actual θ to θ 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-Δ effect can be expressed in terms of τ. b)The maximum plastic deformation of a structure under the influence of P-Δ effect can be expressed in terms of τ. Empirical formula for average deformation response were presented. d)As a value corresponds to the collapse of frames, the critical stability ratio was presented.
