SOME ASPECTS OF ENERGY METHODS FOR THE INELASTIC SEISMIC RESPONSE OF DUCTILE SDOF STRUCTURES

This paper explores some aspect of energy demands for single-degree-of -freedom (SDOF) systems. Energy response time histories for simple pul ses or sine-wave ground excitations are constructed and the behaviour of each contributing factor to the energy balance is studied. Examples are used to illustrate the fundamental behaviour of the kinetic energ y, strain energy, energy dissipated through normal damping, energy dis sipated through permanent deformations, and total input energy, the la tter always being equal to the sum of the others throughout the dynami c response. It is found that: firstly, energy methods produce good ind icators of the nonlinear inelastic seismic structural performance; sec ondly, the absolute energy method has some practical shortcomings, par ticularly regarding the definition of input and kinetic energies; thir dly, the relative energy method has a closer relationship to the param eters of engineering interest; and finally, if only hysteretic energy is of interest, both the absolute and relative energy methods can be u sed, unless normalization by input energy is sought.