The development and the validation of proper capacity models for displacement-based assessment and nonlinear modelling of Reinforced Concrete (RC) members are certainly paramount both for pre-normative guidelines and for the seismic fragility analysis of existing buildings. Existing models for deformation capacity assessment and modelling of RC columns and beam-column joints are generally based on elements reinforced with deformed bars. Nevertheless, a significant portion of existing pre-1970 Italian buildings is reinforced with plain bars. The post-elastic response and the corresponding cyclic degradation in members with plain bars can be significantly different with respect to members with deformed bars, mainly due to the influence of lower bond capacities on deformation mechanisms. Additionally, beam-column joints with plain bars are usually unreinforced, thus vulnerable to shear failures, and they generally exhibited a peculiar failure mechanism with respect to joints with deformed bars, leading to the detachment of a concrete wedge from the beam-column intersection. In this study, a modelling strategy for RC frames with plain bars is proposed and applied. An empirical-based approach for the nonlinear modelling and deformation capacity assessment of flexure-controlled RC columns with plain bars is proposed, based on a properly collected experimental database. Empirical predictive equations are carried out for yielding, maximum, “ultimate”, and zero-resistance conditions. An empirical macro-modelling approach is also formulated for unreinforced joints with hook-ended plain bars, suitable for extensive nonlinear analyses. Based on collected experimental data, a joint shear strength model is proposed, and the joint panel constitutive parameters are defined to reproduce the cyclic experimental joint shear stress-strain behaviour. The whole modelling approach is first validated through the comparison with beam-column sub-assemblages experimentally tested and presented in the literature. Then, a complete case-study 2/3- scaled 3-bay-3-storey RC frame designed for gravity loads only, reinforced with plain bars and representative of typical Italian pre-1970 buildings, has been numerically reproduced. These predictions are finally compared with the experimental evidence carried out on a pseudo-static test performed on this frame in the past and presented in the literature to assess the prediction capacity of the proposal.
Nonlinear modelling of non-conforming concrete frames reinforced with plain bars / De Risi, M. T.; Ricci, P.; Verderame, G. M.; Manfredi, G.. - (2019), pp. 1485-1498. (Intervento presentato al convegno fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures tenutosi a pol nel 2019).
Nonlinear modelling of non-conforming concrete frames reinforced with plain bars
De Risi M. T.;Ricci P.;Verderame G. M.;Manfredi G.
2019
Abstract
The development and the validation of proper capacity models for displacement-based assessment and nonlinear modelling of Reinforced Concrete (RC) members are certainly paramount both for pre-normative guidelines and for the seismic fragility analysis of existing buildings. Existing models for deformation capacity assessment and modelling of RC columns and beam-column joints are generally based on elements reinforced with deformed bars. Nevertheless, a significant portion of existing pre-1970 Italian buildings is reinforced with plain bars. The post-elastic response and the corresponding cyclic degradation in members with plain bars can be significantly different with respect to members with deformed bars, mainly due to the influence of lower bond capacities on deformation mechanisms. Additionally, beam-column joints with plain bars are usually unreinforced, thus vulnerable to shear failures, and they generally exhibited a peculiar failure mechanism with respect to joints with deformed bars, leading to the detachment of a concrete wedge from the beam-column intersection. In this study, a modelling strategy for RC frames with plain bars is proposed and applied. An empirical-based approach for the nonlinear modelling and deformation capacity assessment of flexure-controlled RC columns with plain bars is proposed, based on a properly collected experimental database. Empirical predictive equations are carried out for yielding, maximum, “ultimate”, and zero-resistance conditions. An empirical macro-modelling approach is also formulated for unreinforced joints with hook-ended plain bars, suitable for extensive nonlinear analyses. Based on collected experimental data, a joint shear strength model is proposed, and the joint panel constitutive parameters are defined to reproduce the cyclic experimental joint shear stress-strain behaviour. The whole modelling approach is first validated through the comparison with beam-column sub-assemblages experimentally tested and presented in the literature. Then, a complete case-study 2/3- scaled 3-bay-3-storey RC frame designed for gravity loads only, reinforced with plain bars and representative of typical Italian pre-1970 buildings, has been numerically reproduced. These predictions are finally compared with the experimental evidence carried out on a pseudo-static test performed on this frame in the past and presented in the literature to assess the prediction capacity of the proposal.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
