Nonlinear Seismic Response of Irregularly Masonry-Infilled R.C. Framed Buildings Retrofitted With Hysteretic Damped Braces


Abstract eng:
An irregular in-elevation distribution of the infill walls in a reinforced concrete (r.c.) framed building can produce significant variations in stiffness, strength and mass distribution leading to severe seismic damage. To mitigate these effects and retrofit the structure, hysteretic damped braces (HYDBs) can be suitably inserted in the framed structure. The retrofitting criteria are aimed to obtain a damped braced structure globally regular with regard to stiffness and strength. In detail, the stiffness distribution of HYDBs is evaluated consistently with a constant value of the drift ratio of the damped braced frame along the building height; moreover, the strength distribution of the HYDBs is assumed so that their activation tends to occur at every storey simultaneously, before reaching the shear resistance of the infilled framed structure. For proportioning the HYDBs, a Displacement-Based Design (DBD) procedure, in which the design starts from a target deformation of an equivalent elastic linear system, is adopted in the present work. To check the effectiveness and reliability of the DBD procedure, a numerical investigation is carried out with reference to a six-storey r.c. framed building, which, originally designed according to an old Italian seismic code (1996) for a medium-risk zone, has to be retrofitted by inserting of HYDBs to attain performance levels imposed by the current Italian code (NTC 2008) in a high-risk zone. It is supposed that the irregularity is consequent to a change in use of the first two floors, from residential to office, substituting the masonry infills of the first three storeys with glass windows. Nonlinear dynamic analyses of the unbraced, irregularly infilled and damped braced infilled frames are carried out by a step-by-step procedure, considering sets of artificially generated and real ground motions, whose response spectra match those adopted by NTC 2008 for different performance levels. To this end, r.c. frame members are idealized by a two-component model, assuming a bilinear moment-curvature law and considering the effect of the axial load on the ultimate bending moment of the columns. The response of an HYDB is idealized by a bilinear law, preventing buckling. Finally, masonry infills are represented as equivalent diagonal struts reacting only in compression according to an elastic-brittle law. Even though more refined analytical models can be used to simulate the hysteretic response of r.c. members and infill walls, the design procedure prove to be effective in the mitigation of the effects of the in-elevation irregular distribution of the infill walls.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 476.:
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