On the influence of ductility on the computation of the response of 1 dof system with superimposed static loads

Structure do yield even under normal loading conditions, in particular stress concentration areas, (e.g. elbows in piping) and a large energy dissipation takes place in such spots. This energy dissipation is instrumental in the reduction of the maximum amplitude of the displacement under load. Hence in reality the strong peaks as predicted using purely elastic methods are not present due to the energy dissipation during hysteretic cycles. Besides the structural softening due to yielding causes changes in the frequency characteristics which have a large beneficial effect on the response in the peak region. This is particularly true in the case of the strongly peaked floor response spectra (FRS), where a slight change in the frequency may lead to a substantial reduction in the amplification. On the other hand ratcheting may take place as a consequence of the superposition of static and dynamic loads leading to excessive strains.