Novel design procedure for steel hysteretic dampers in seismic retrofit of frame structures

An energy-based design procedure for sizing dissipative bracing systems equipped with steel hysteretic dampers is proposed for application to the seismic retrofit of frame structures. The procedure is based on the following assumptions: it is not iterative, as it provides a direct estimation of the steel dissipater sizes; the stiffening effects of dampers reduce displacements below prefixed limits; their damping effects reduce displacements and stress states to keep the response of structural members within their safe domains up to medium-to-high levels of the input seismic action. The procedure is articulated in three steps: seismic assessment analysis in current state and definition of the elastic properties of the bracing system to be installed in the structure; design of the dampers; verification of the seismic performance of the structure in retrofitted conditions. A demonstrative case study concerning a precast reinforced concrete frame school building is offered to explicate the practical application of the procedure, as well as to evaluate the enhancement of its response generated by the intervention. The latter consists in incorporating a dissipative bracing system equipped with triangular-shaped added damping and stiffness (T-ADAS) steel hysteretic devices. The two limit hypotheses assumed in the computational analyses for the roof beam-to-column connections of the building, i.e. hinges or fixed-ends, allow to discuss how the fundamental period of the structure in current conditions affects the parameters involved in the sizing process of the T-ADAS dampers.