Nonlinear Dynamic Analysis of In-Plan Irregular R.C. Structures Retrofitted With Hysteretic Damped Braces


Abstract eng:
The seismic retrofitting of unsymmetric plan reinforced concrete (r.c.) framed buildings can be carried out by the insertion of damped braces (DBs), which are made of steel braces connecting two consecutive storeys and incorporating energy dissipating devices. Yet most of the proposals to mitigate the seismic response of asymmetric framed buildings by DBs rest on the hypothesis of elastic (linear) structural behaviour. The aim of the present work is to evaluate the effectiveness and reliability of a Displacement-Based Design procedure of hysteretic damped braces (HYDBs) based on the nonlinear behaviour of the frame members. An expression of the biaxial viscous damping equivalent to the hysteretic energy dissipated by the damped braced frame is assumed under bidirectional seismic loads, where corrective factors are adopted as a function of design parameters of the HYDBs. Moreover, the extended N2 method considered by Eurocode 8, which combines the nonlinear static analysis along the principal in-plan directions of the structure with elastic modal analysis, is adopted to evaluate the higher mode torsional effects. To this end, the Town Hall of Spilinga (Italy), a reinforced concrete framed structure with an L-shaped plan built at the beginning of the 1960s, is supposed to be retrofitted with HYDBs to attain performance levels imposed by the Italian seismic code (NTC08) in a high-risk zone. Ten structural solutions are compared by considering two alternative in-plan distributions of the HYDBs, to eliminate (elastic) torsional effects, and different design values of the frame ductility combined with a constant design value of the damper ductility. Reinforced concrete (r.c.) structures with asymmetric plan may require the assessment of the critical incident angle of bidirectional ground motions. To this end, a computer code for the nonlinear dynamic analysis of r.c. spatial framed structures is adopted. Frame members are simulated with a lumped plasticity model, including flat surface modelling of the axial load-biaxial bending moment elastic domain, at the end sections of r.c. beams and columns where inelastic deformations generally occur, while a bilinear law is used to idealize the behaviour of a HYDB. Vulnerability index domains of r.c. frame members and HYDBs are adopted to estimate the directions of least seismic capacity, considering artificial ground motions whose response spectra match those adopted by NTC08 at serviceability and ultimate limit states.

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



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


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