Energy-Based Design Criterion of Dissipative Bracing Systems for the Seismic Retrofit of Frame Structures

Abstract

Featured Application: An energy-based sizing criterion is proposed to help designing dissipative bracing systems incorporating fluid viscous spring-dampers for the seismic retrofit of frame structures.Abstract: Direct sizing criteria represent useful tools in the design of dissipative bracing systems for the advanced seismic protection of existing frame structures, especially when incorporated dampers feature a markedly non-linear behaviour. An energy-based procedure is proposed herein to this aim, focusing attention on systems including fluid viscous devices. The procedure starts by assuming prefixed reduction factors of the most critical response parameters in current conditions, which are evaluated by means of a conventional elastic finite element analysis. Simple formulas relating the reduction factors to the equivalent viscous damping ratio of the dampers, ξ eq , are proposed. These formulas allow calculating the ξ eq values that guarantee the achievement of the target factors. Finally, the energy dissipation capacity of the devices is deduced from ξ eq , finalizing their sizing process. A detailed description of the procedure is presented in the article, by distinguishing the cases where the prevailing structural deficiencies are represented by poor strength of the constituting members, from the cases having excessive horizontal displacements. A demonstrative application to the retrofit design of a reinforced concrete gym building is then offered to explicate the steps of the sizing criterion in practice, as well as to evaluate the enhancement of the seismic response capacities generated by the installation of the dissipative system.

Roof Isolation and Girder-to-Column Dissipative Connections in Seismic Design of Precast R/C Structures

“…The FV devices considered as dissipative devices in this first design strategy, belonging to the general class of spring-dampers adopted in anti-seismic design [19][20][21][22][23][24], have been extensively studied by the authors for applications to new structures and infrastructures [25][26][27] and retrofit of existing ones [28][29][30][31][32]. The response of the steel-PTFE bearings was modelled by a "friction isolator" element, characterized by a Coulomb-type hysteretic response law.…”

“…As illustrated by the drawings in Figures 5 and 6, the dissipaters are always installed in pairs, and namely: with in-parallel diagonal layout at the 14 girder-to-column connections, in the X-Z vertical plan (A-type FV spring-dampers, 28 in total); with in-series horizontal layout at both ends of two HEB 220 steel beams linking the column top sections and the base "bulbs" of the girders, per each longitudinal side of the building, in the Y-Z vertical plan (B-type, eight in total). The FV devices were designed by referring to the criterion proposed in [25], recently updated in [32], for any type of protective system incorporating them. The criterion consists in assigning the spring-dampers the capability of dissipating a prefixed energy fraction, Ed,t, of the seismic input energy, Ei,t.…”

“…The criterion consists in assigning the spring-dampers the capability of dissipating a prefixed energy fraction, Ed,t, of the seismic input energy, Ei,t. By targeting an elastic response of the structure up to the MCE, and by also considering the frictional contribution to the energy dissipation balance supplied by the steel-PTFE bearings, Ed,t The FV devices were designed by referring to the criterion proposed in [25], recently updated in [32], for any type of protective system incorporating them. The criterion consists in assigning the spring-dampers the capability of dissipating a prefixed energy fraction, E d,t , of the seismic input energy, E i,t .…”

“…Based on these choices, the total nominal energy dissipation capacities of the A-type and B-type sets of devices result to be very similar (196 kNm-A, against 200 kNm-B). The in-series mounting scheme of the B-type device pairs allows mutually pre-stressing them up to half-stroke, thus obtaining continuous (i.e., not origin-passing) response cycles, like for other supplemental damping systems where FV spring-dampers are installed horizontally [25][26][27][28][29][30][31][32].…”

Advanced Seismic Retrofit of a Mixed R/C-Steel Structure

“…The FV dissipaters were sized by applying the procedure proposed in [41]. Based on its open formulation, it can be easily extended to reticular steel elements, like the ones constituting the skeleton of the two upper storeys of the case study building, which are mainly affected by low axial force buckling limits of the constituting profiles.…”