PSI - Issue 64

Massimiliano Ferraioli et al. / Procedia Structural Integrity 64 (2024) 1025–1032 Ferraioli et al./ Structural Integrity Procedia 00 (2019) 000–000

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The retrofit strategy and design procedure effectively ensure nearly uniform yielding of steel slit dampers, as demonstrated in Fig. 10, depicting hysteresis loops of selected dampers across different floors under earthquake ground motions for the Collapse Prevention Limit State. Moreover, the existing building structures undergo assessment regarding chord rotation for the Collapse Prevention (CP) Limit state (Fig.12). 5. Conclusions This paper proposes the seismic retrofit of an existing RC building using two alternative retrofit strategies based on dissipative exoskeletons. The first one uses an orthogonal exoskeleton composed of concentric braced frames (CBFs) equipped with shape memory alloy dampers (SMADs). The second one employs a parallel exoskeleton composed of eccentric braced frames (EBFs) equipped with steel slit dampers (SSDs). A displacement-based design (DBD) procedure is proposed and applied to size the dissipative exoskeletons. The brace of the CBF is designed to remain elastic without buckling when subjected to an axial force equal to the strength of the SMAD. The shape of the steel strips of SSDs is chosen to optimize energy dissipation and prevent premature buckling failure modes. Nonlinear time-history analysis is conducted to evaluate the retrofit strategy's effectiveness. The results indicate that both the two retrofit strategies based on dissipative exoskeletons are feasible for real existing RC buildings. They are reversible, rapid, low-impact, and can be implemented while the building is in use. Additionally, the design procedure proves effective, with displacement demands aligning well with design values. The results indicate that for the Collapse Prevention Limit State, the Inter-Story Drift (IDR) response does not surpass the permitted transient drift limit of 2% across all considered ground motions. Additionally, the dissipative exoskeleton effectively mitigates torsional effects. The performance chord rotation ratio remains below one for every earthquake scenario, indicating the retrofit strategy effectively prevents all ductile failure modes. Finally, it should be noted that connections between the exoskeletons and the existing structures were not considered in the analyses, which could affect the feasibility of the intervention. References Applied Technology Council, 1996. Seismic evaluation and retrofit of concrete buildings, vol 1, Report no ATC 40. Redwood City. Cao, X.Y., Shen, D., Feng, D.C., Wang, C.L., Qu, Z., Wu, G. 2022. Seismic retrofitting of existing frame buildings through externally attached sub structures: State of the art review and future perspectives. J. Build. Eng. 57, 104904. De Matteis, G., Ferraioli, M., Raimo, R., Lavino, A., Bencivenga, P., 2022. Design of metal shear panels for seismic protection of RC buildings. Lecture Notes in Civil Engineering 262 LNCE, 898–906. Di Lorenzo, G., Colacurcio, E., Di Filippo, A., Formisano, A., Massimilla, A., Landolfo, R., 2020. State-of-the-art on steel exoskeletons for seismic retrofit of existing RC buildings. Ingegneria Sismica 37, 33-50. Casagrande, L., Menna, C., Asprone, D., Ferraioli, M., Auricchio, F., 2021. Buildings. Shape Memory Alloy Engineering: For Aerospace, Structural, and Biomedical Applications, 689–729. Ferraioli, M., Nuzzo, D., Concilio, A, 2019. Shape memory alloys for earthquake building protection, Proceedings of SPIE - The International Society for Optical Engineering, 10970, 109701M. Ferraioli, M., Lavino, A., Mandara, A. 2020. Seismic retrofit design method of RC buildings using metallic yielding dampers. Ingegneria Sismica 37(1),19–32. Ferraioli, M., Lavino, A., Molitierno, C., Di Lauro, G., 2021. Seismic retrofit of an existing reinforced concrete building with buckling restrained brace. The Open Civil Engineering Journal 15, 203-225. Ferraioli, M., Concilio, A., Molitierno, C., 2022. Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces. Earthquake Engineering and Engineering Vibration 21(3), 785-809. Ferraioli, M., Lavino, A., De Matteis, G. 2023a. A design method for seismic retrofit of reinforced concrete frame buildings using aluminum shear panels. Archives of Civil and Mechanical Engineering 23(2), 106. Ferraioli, M., Laurenza, B., Lavino, A., Frattolillo, C., De Matteis, G. 2023b. Seismic retrofit of a steel-reinforced concrete hospital building using continuous energy-dissipative steel columns. Steel and Composite Structures 47(4), 467-488. Lee, C.H., Ju, Y.K., Min, J.K., Lho, S.H., Kim, S.D., 2015. Non-uniform steel strip dampers subjected to cyclic loadings. Eng. Struct. 99, 192–204. Mander, J.B., Priestley, M.J.N., Park, R. 1988. Theoretical stress-strain model for confined concrete. J. Struct. Eng. 114(8), 1804-1826. Mazza, F., Vulcano, A., 2015. Displacement-based design procedure of damped braces for the seismic retrofitting of r.c. framed buildings. Bulletin of Earthquake Engineering 13(7), 2121-2143. NTC-Guidelines. 2018. Technical Standards for Constructions, Official Journal of the Italian Republic, Rome. Qiu, C., Zhu, S., 2017. Shake table test and numerical study of self-centering steel frame with SMA braces. Earthquake Engineering and Structural Dynamics 46(1), 117–137. Seismosoft. 2023. SeismoStruct - a computer program for static and dynamic nonlinear analysis of framed structures. https://seismosoft.com.