Abstract
The total energy input made by an earthquake depends mainly on the total mass and the fundamental natural period of the structure and is scarcely affected by the strength and the type of restoring force characteristics. On the other hand the concentration of the input energy depends mainly on vertical distribution of strength and the type of restoring force characteristics. The energy concentration into relatively weak story often causes the collapse of the structure and must be carefully prevented in design practice. This paper deals with the basic feature of the energy concentration in shear-type multi-story buildings which are not structurally uniform and are composed of different structural elements as is usually encountered. One is the structure combined with rigid frames and braced frame in a same plane frame. In this type of structure inelastic strain energy is mainly cumulated in the rigid frames and the braced frame only serves to restrict excessive overall displacement. Relaxation of braces produces reduction of strength and causes the energy concentration. Another is the rigid frame structure which exhibits partly different elastic limit deformation and the frame with larger elastic limit deformation is hardly strained inelastically. Such non-collaboration of structural elements also causes the energy concentration of multi-story buildings. These phenomena can be well explained by the basic law on the energy distribution which has been already proposed by the author, and also the relation between overall maximum drift and cumulated inelastic deformation of these type of structures is expressed in simple empirical formulas.
