Displacement-Based Design of Dissipative Braces at a Given Performance Level of a Framed Building

Abstract eng:
The insertion of dissipative braces proves to be very effective in order to enhance the performance of a framed building under seismic loads. For a widespread application of this technique, practical design procedures are needed. In this paper a design procedure aiming to proportion damped braces in order to attain, for a specific level of seismic intensity, a designated performance level of the structure is proposed. Exactly, a proportional stiffness criterion, which assumes the elastic lateral storey-stiffness due to the braces proportional to that of the unbraced frame, is combined with the Direct Displacement-Based Design, in which the design starts from a target deformation. To check the reliability of the design procedure, a six-storey reinforced concrete (r.c.) plane frame, representative of a medium-rise symmetric framed building, is considered as a test structure, which primarily designed in a medium-risk seismic region, has to be retrofitted as in a high-risk seismic region by insertion of braces equipped with either hysteretic dampers or viscoelastic ones. Nonlinear dynamic analyses are carried out, under real and artificially generated ground motions, by a step-by-step procedure. Frame members and hysteretic dampers are idealized by bilinear models, while the viscoelastic dampers are idealized by a six-element generalized model describing the variation of the mechanical properties depending on the frequency, at a given temperature.

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