GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 2.2 350 Conclusions Seismic retrofit of existing Reinforced Concrete (RC) structures is investigated in this study. The attention is focused on the potential of steel exoskeletons. The weakness of traditional exoskeletons, as it has been noticed also in this study (MOD_01), is that they are usually designed to remain elastic under seismic load, so that the potential ductility and resistance of the steel members cannot be totally exploited and at the end of a seismic event also the RC building presents damage to the structural elements. For this reason, a careful consideration in this study is paid to the seismic assessment of a hybrid solution based on the use of steel exoskeletons and base sliding devices for the RC frame to retrofit (i.e., planar steel-PTFE sliding devices). The role of some key mechanical parameters is first explored for a simple Single Degree of Freedom (SDOF) model, representative of the hybrid system. Successively, based on the preliminary SDOF outcomes, the efficiency of the proposed solution is further assessed for a plane multi-storey RC frame. In this case, the non-linear analysis of the assembled solution confirms the validity and potential of the proposed approach, compared to traditional steel exoskeletons. In the proposed solution (MOD_02), ductility and resistance of the steel bracing can be totally exploited for the retrofit of the existing building, so that nearly no damage is expected in the RC building after a seismic event, that means also very low costs for retrofit after a seismic event (reasonably, the cost of brace replacement at the ground level of the exoskeleton). Based on the positive outcomes of the preliminary SDOF and 2D-MDOF studies presented in this paper, the research should be extended to 3D structural models, in order to find the key details that can influence the efficiency of the proposed solution. References Badini L., De Stefano C.A. and Custodi A.; 2019: Seismic Strengthening of Existing RC Structure Through External 3D Exoskeleton . Proceedings of the 20 th IABSE Congress, New York City, 2019 - The Evolving Metropolis, pp. 1018-1024, doi: 10.1080/10168664.2019.1599209 Di Lorenzo G., Colacurcio E., Di Filippo A., Formisano A., Massimilla A. and Landolfo R.; 2020: State-of-the- art on steel exoskeletons for seismic retrofit of existing RC buildings . Ingegneria Sismica - International Journal of Earthquake Engineering, 37(1): 33-50 Di Sarno L. and Manfredi G.; 2012: Experimental tests on full-scale RC unretrofitted frame and retrofitted with buckling-restrained braces . Earthquake Engineering & Structural Dynamics, 41(2): 315-333 Dolce M., Cardone D. and Croatto F.; 2005: Frictional Behavior of Steel-PTFE Interfaces for Seismic Isolation . Bull Earthquake Eng, 3: 75-99, doi: 10.1007/s10518-005-0187-9 Faiella D., Calderoni B. and Mele E.; 2020: Seismic Retrofit of Existing Masonry Buildings through Inter-story Isolation System: A Case Study and General Design Criteria . Journal of Earthquake Engineering, doi: 10.1080/13632469.2020.1752854 Labò S., Passoni C., Marini A. and Belleri A.; 2020: Design of diagrid exoskeletons for the retrofit of existing RC buildings . Engineering Structures, 220: 110899, doi: 10.1016/j.engstruct.2020.110899 Martelli L., Restuccia L. and Ferro G.A.; 2020: The exoskeleton: a solution for seismic retrofitting of existing buildings . Procedia Structural Integrity, 25: 294-304 Scuderi G.; 2016: Building Exoskeletons for the Integrated Retrofit of Social Housing . Civil Engineering Journal, 2(6); doi: 10.28991/cej-2016-00000029 Corresponding author: ljuba.sancin@gmail.com