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Spectral and fragility evaluations
of retrofitted structures through
strength reduction and enhanced damping
Gian Paolo Cimellaro 1, Hwasung Roh 2 and
Alessandro De Stefano 1
1. Department of Structural & Geotechnical Engineering (DISTR),
Polytechnic of Turin, Turin, Italy
2. Department of Civil, Structural & Environmental Engineering,
University at Buffalo, The State University of New York, Buffalo, USA
Abstract: A retrofit procedure for existing buildings called the
¡°weakening and damping technique¡± (WeD) is presented in this paper.
Weakening of structures can limit the maximum response accelerations
during severe ground motions, but leads to an increase in the
displacements or inter-story drifts. Added damping by using viscous
dampers, on the other hand, reduces the inter-story drifts and has no
significant effect on total accelerations, when structures behave
inelastically. The weakening and damping technique addresses the two
main causes for both structural and nonstructural damage in structures.
The weakening retrofit is particularly suitable for structures that have
overstressed components and weak brittle components. In this paper, the
advantages of the WeD are verified by nonlinear dynamic analysis and
simplified spectral approach that
has been modified to fit structures with additional damping devices. A
hospital structure located in the San Fernando Valley in California is
selected as a case study. The results from both analyses show that the
retrofit solution is feasible to reduce both structural acceleration and
displacement. A sensitivity analysis is also carried out to evaluate the
effectiveness of the retrofitting method using different combinations of
performance thresholds in accelerations and displacements through
fragility analysis.
Keywords: weakening; damping; retrofit; inelastic spectral
response; fragility analysis; nonlinear dynamic analysis
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