抄録
Energy balance equation during catastrophic earthquake can be written as follows based on the energy concept introduced by G. W. Housner, that is, [numerical formula] where M_T : Total mass of frame S_V : Pseudo velocity response spectrum E^G : Work done by gravity load during earthquake E^e : Internal work of overall frame Each term of this equation can be expressed as a function of required seismic load under the assumption that the plastic drift occurs only in one direction. Therefore, seismic design load represented by the ultimate base shear coefficient and the shear force distribution coefficient is obtained analyticaly from energy balance equation. This paper mainly deals with the ultimate base shear coefficient (C_<Bu>) required for the frames which result in the beam and brace yield type sway collapse mechanism. The significant aspects of analytical results are summarized in the following : 1. Internal work of overall frame is in proportion to the square of the number of story. Consequently, as the number of story increases, required value of C_<Bu> falls hyperbolically. 2. C_<Bu> is affected directly by the plastic deformability of frame, while it is hardly affected by the weight and the shape of frames except for the the number of story. 3. C_<Bu> of braced frames is smaller than that of unbraced frames about 10-20%.
