It has been recognized since many years that displacements represent the most significant index of the state of a structure under seismic attack. The advent of performance-based earthquake engineering has placed an emphasis on simulating nonlin ear response of structures to seismic excitations and so new procedures, based on comparison between the capacity and demand, both determined in terms of displacements rather than strengths, have been proposed for seismic assessment and design. Hence, a reliable estimate of the displacement capacity of structures represents a key point. However, modeling of beam-column members in non-linear range the definition of a plastic region is still an open problem. Finite element models for nonlinear material response of beam-column members belong to two fundamental categories: lumped-plasticity and distributed-plasticity ones. In the present work nonlinear static analyses have been performed on single reinforced concrete column elements and a 2D frame structure by adopting both approaches and a comparison between results is illustrated. In particular sensitivity of the structural response to the different choices taken in the modelling procedure is underlined. With a fibre modelling the “strain localization” phenomenon determines non-objective results, especially in terms of ultimate displacement. A correction technique for the adopted discretization is proposed by comparing numerical results obtained from fibre analyses on single column elements with those coming from a simplified procedure (Priestley et al. 2007) used to get the capacity curve for these members. This comparison allows to get useful information about the discretization to use in a fibre modelling. Results pushover analyses performed with fibre approach have been used also to get indication about reasonable values of plastic hinge length that may be used in a lumped-plasticity modelling. Then, results of these kind of analyses carried out on single column members have been used to model a whole frame structure by both distributed and concentrated plasticity models. The results obtained from fiber model with different discretizations of the members and lumped-plasticity approach with different values of plastic length have been compared and commented.
Distributed and Lumped-Plasticity Approaches for Modeling RC Frame Structures under Seismic Action
FERRACUTI, BARBARA;SAVOIA, MARCO;
2009
Abstract
It has been recognized since many years that displacements represent the most significant index of the state of a structure under seismic attack. The advent of performance-based earthquake engineering has placed an emphasis on simulating nonlin ear response of structures to seismic excitations and so new procedures, based on comparison between the capacity and demand, both determined in terms of displacements rather than strengths, have been proposed for seismic assessment and design. Hence, a reliable estimate of the displacement capacity of structures represents a key point. However, modeling of beam-column members in non-linear range the definition of a plastic region is still an open problem. Finite element models for nonlinear material response of beam-column members belong to two fundamental categories: lumped-plasticity and distributed-plasticity ones. In the present work nonlinear static analyses have been performed on single reinforced concrete column elements and a 2D frame structure by adopting both approaches and a comparison between results is illustrated. In particular sensitivity of the structural response to the different choices taken in the modelling procedure is underlined. With a fibre modelling the “strain localization” phenomenon determines non-objective results, especially in terms of ultimate displacement. A correction technique for the adopted discretization is proposed by comparing numerical results obtained from fibre analyses on single column elements with those coming from a simplified procedure (Priestley et al. 2007) used to get the capacity curve for these members. This comparison allows to get useful information about the discretization to use in a fibre modelling. Results pushover analyses performed with fibre approach have been used also to get indication about reasonable values of plastic hinge length that may be used in a lumped-plasticity modelling. Then, results of these kind of analyses carried out on single column members have been used to model a whole frame structure by both distributed and concentrated plasticity models. The results obtained from fiber model with different discretizations of the members and lumped-plasticity approach with different values of plastic length have been compared and commented.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
