The seismic vulnerability of infilled reinforced concrete (RC) frames built in the Mediterranean earthquake prone regions before the 70’s has been assessed by many post-earthquake surveys and several experimental studies. Beyond the lack of seismic-resistant detailing in the frame elements, a relevant source of vulnerability for these structural typology is represented by the in-plane interaction between the frame and the infills. Infills are typically made of masonry, selected for its good thermal and acoustic insulation performance and characterized by high stiffness and strength, but coupled with a brittle post-peak behavior. During an earthquake, the different stiffness and deformation capacity characterizing the infill and the frame can lead to severe damage, including widespread cracking and crushing in the former, and brittle shear failures in the latter. When dealing with the seismic retrofit of an existing infilled RC building, this local interaction cannot be ignored, as it could jeopardize the efficiency of the seismic retrofit intervention by triggering unexpected early collapses in the existing frame. In order to mitigate this issue, in the present paper an infill isolation technique is presented, conceived to reduce the infill-frame in-plane interaction (downgrade). The downgrade is obtained by isolating the infill from the surrounding frame with a cut on a portion of the infill perimeter. A specific innovative wall-to-frame beam connection is implemented, which promotes the masonry arching mechanism against out-of-plane actions, while ensuring in-plane relative sliding. In the paper, the experimental cyclic in-plane and out-of-plane response of a real scale specimen downgraded with the proposed technique are presented and some issues about the conceptual design of the intervention and its invasiveness are discussed.
Experimental assessment of an innovative isolation technique for the seismic downgrade of existing masonry infills
Bolis V
;Paderno A;Preti M
2020-01-01
Abstract
The seismic vulnerability of infilled reinforced concrete (RC) frames built in the Mediterranean earthquake prone regions before the 70’s has been assessed by many post-earthquake surveys and several experimental studies. Beyond the lack of seismic-resistant detailing in the frame elements, a relevant source of vulnerability for these structural typology is represented by the in-plane interaction between the frame and the infills. Infills are typically made of masonry, selected for its good thermal and acoustic insulation performance and characterized by high stiffness and strength, but coupled with a brittle post-peak behavior. During an earthquake, the different stiffness and deformation capacity characterizing the infill and the frame can lead to severe damage, including widespread cracking and crushing in the former, and brittle shear failures in the latter. When dealing with the seismic retrofit of an existing infilled RC building, this local interaction cannot be ignored, as it could jeopardize the efficiency of the seismic retrofit intervention by triggering unexpected early collapses in the existing frame. In order to mitigate this issue, in the present paper an infill isolation technique is presented, conceived to reduce the infill-frame in-plane interaction (downgrade). The downgrade is obtained by isolating the infill from the surrounding frame with a cut on a portion of the infill perimeter. A specific innovative wall-to-frame beam connection is implemented, which promotes the masonry arching mechanism against out-of-plane actions, while ensuring in-plane relative sliding. In the paper, the experimental cyclic in-plane and out-of-plane response of a real scale specimen downgraded with the proposed technique are presented and some issues about the conceptual design of the intervention and its invasiveness are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
