PSI - Issue 44

5

Marco Gaetani d’Aragona et al. / Procedia Structural Integrity 44 (2023) 1052–1059 Author name / Structural Integrity Procedia 00 (2022) 000–000

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To enhance the seismic performances of infilled RC frames, a number of possible retrofit strategies can be employed. In particular, the behavior of existing frames can be improved by preventing the triggering of premature brittle failures via increasing of member capacity in terms of ductility and/or strength. As an alternative, limiting frame lateral deformations may avoid damage to non-structural components, possibly allowing uniform distribution of lateral deformations along the height and thus preventing the development of soft-story collapse mechanism. Fast interventions may be implemented to avoid building use restrictions of for a long period (e.g., FRP jacketing). However, this strategy is generally adopted to avoid the development of shear failure, while it is not effective in lateral drift reduction. In this study two different retrofit options are considered, the first corresponds to FRP jacketing of relevant RC members, while the second to RC jacketing to increase the global strength and stiffness of the frames. Retrofit interventions are designed and applied suitably modifying the interstory backbone. More details on the implemented procedure are reported in Gaetani d’Aragona et al. (2022b). 3. Example of pushover curves for as-built and retrofitted ‘50s building In this section, the simplified procedure proposed to generate interstory backbones is adopted to build Stick model for a reference 5-story building designed in the ‘50s for gravity-loads (GLD) only. By assuming as input variables, a constant interstory height of 3.2m, an in-plan surface equal to 600m 2 with L/B=2, medium consistency infills, and a constant opening percentage along the height equal to 20% a set of compatible architectural layouts is generated. Only the first compatible layout is considered for brevity purposes. The proposed simplified procedure allows to account for modeling of possible brittle failures induced by infill-frame interactions, and the incidence of beam-column joint behavior on the building capacity. To show the impact of different assumptions regarding brittle failure in modeling, Figure 3(a) shows the Stick nonlinear response when subjected to increasing loads proportional to the first-mode shape in the longitudinal direction. In particular, the pushover analysis is performed to evidence the combined effect of beam-column joint failure (JF) and beam-column failure (BCF) on the global frame response.

(a) (b) Fig. 3. (a) As-built and (b) retrofitted building pushover curves (first-mode proportional load). For as-built frame, curves show the effect of brittle failures for columns and beams (B/C-failure) and for beam-column joints (J-failure) for as-built frame. For retrofitted frame, the effect of FRP-S and RCJ-S retrofit strategies are evidenced with respect to as-built configuration.