The insertion of steel bracing systems equipped with dissipative devices is a widely used technique for the seismic retrofitting of reinforced concrete (r.c.) framed buildings; yet, few attempts have been made so far to construct an external arrangement in the form of a double skin. The dissipative exoskeleton (DEX) appears convenient from energetic and functional points of view. It eliminates the indirect costs associated with downtime during retrofitting and cuts out the unwanted effects to the existing structure that commonly arise with the dissipative endoskeleton. This paper provides a DEX sizing procedure through use of overdamped elastic response spectra, which could prove a valuable tool for practitioners. The DEX is designed on the assumption of a rigid coupling with the existing structure, making a distinction between mass and stiffness properties of the steel exoskeleton and added damping of the dissipative bracing system. Concentrically braced chevron frames with pinned joints and damped bracing systems incorporating fluid viscous dampers (FVDs) are considered. Elastic‐linear behaviour of steel frame members and nonlinear pure viscous dashpot for FVDs, with a storey‐shear proportional distribution, are hypothesised. The retrofitting of a six‐storey r.c. framed structure, representative of the Italian residential buildings designed for moderate seismic loads during the 1990s, is to be simulated in a high risk‐seismic region. Three external arrangements of DEX are selected: parallel (DEX.Pa) and perpendicular (DEX.Pe) to all façades of the existing building and a mixed solution (DEX.Mi) with both parallel and perpendicular disposition placed along the shorter façades without apertures. Nonlinear structural models of the original (F) and coupled (DEXF) structures are developed in OpenSEES, considering ductile and brittle failure modes of r.c. elements and joints. The seismic analyses not only confirm the effectiveness of the proposed DEX design but also provide insights into the strength and weaknesses of the examined configurations.

Dissipative steel exoskeletons for the seismic control of reinforced concrete framed buildings

Fabio Mazza
2020

Abstract

The insertion of steel bracing systems equipped with dissipative devices is a widely used technique for the seismic retrofitting of reinforced concrete (r.c.) framed buildings; yet, few attempts have been made so far to construct an external arrangement in the form of a double skin. The dissipative exoskeleton (DEX) appears convenient from energetic and functional points of view. It eliminates the indirect costs associated with downtime during retrofitting and cuts out the unwanted effects to the existing structure that commonly arise with the dissipative endoskeleton. This paper provides a DEX sizing procedure through use of overdamped elastic response spectra, which could prove a valuable tool for practitioners. The DEX is designed on the assumption of a rigid coupling with the existing structure, making a distinction between mass and stiffness properties of the steel exoskeleton and added damping of the dissipative bracing system. Concentrically braced chevron frames with pinned joints and damped bracing systems incorporating fluid viscous dampers (FVDs) are considered. Elastic‐linear behaviour of steel frame members and nonlinear pure viscous dashpot for FVDs, with a storey‐shear proportional distribution, are hypothesised. The retrofitting of a six‐storey r.c. framed structure, representative of the Italian residential buildings designed for moderate seismic loads during the 1990s, is to be simulated in a high risk‐seismic region. Three external arrangements of DEX are selected: parallel (DEX.Pa) and perpendicular (DEX.Pe) to all façades of the existing building and a mixed solution (DEX.Mi) with both parallel and perpendicular disposition placed along the shorter façades without apertures. Nonlinear structural models of the original (F) and coupled (DEXF) structures are developed in OpenSEES, considering ductile and brittle failure modes of r.c. elements and joints. The seismic analyses not only confirm the effectiveness of the proposed DEX design but also provide insights into the strength and weaknesses of the examined configurations.
design procedure, dissipative steel exoskeletons, nonlinear fluid viscous dampers, r.c. framed buildings, seismic retrofitting
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11770/310711
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