When strong ground motion occurs, frame columns and bridge piers are often subjected at the same time to high axial forces (N), bending moments (M) and shear forces (V). The presence of high shear stresses reduces the structural element strength to combined actions of axial forces and bending moments, the deformation capacity, and the available ductility. Thus, a premature degradation of seismic performance of the structural elements and of the whole structure occurs. Different approaches can be followed for evaluation of N-M-V interaction effects under static or/and seismic actions. A first group is based on the extensions of the well-known formulation by Mörsh , following the indications given by experimental tests. An alternative approach has been furnished by Vecchio and Collins (1988), and involves a more complex procedure that is infeasible for technical applications. Let us stress that N-M-V interaction effects strongly influence the seismic performances of existing buildings that, in absence of seismic codes, have been designed with low transversal reinforcements, unable to give shear strength and confinement actions. In the present paper the influence of the N-M-V interaction on the reduction of the strength of frame beams and columns loaded by high axial force due to dead loads is analysed. To this aim, a model proposed in a recent paper, characterized by a variable slope of the stress fields in the core region of the reinforced concrete section is generalised, in order to be utilized for r.c. elements having rectangular cross sections subjected to seismic actions. The behaviour of elements having low transversal reinforcements for confining action and shear resistance are analysed by evaluation of three dimensional yielding surfaces that take into account the N-M-V interaction, showing that a great reduction of the bending capacities can be estimated. The model is employed for the evaluation of the influence of the N-M-V interaction on the seismic response by pushover analysis of an r.c. frame constructed in the late seventies, for which the mechanical properties of the construction materials have been evaluated by experimental tests. To this aims, the DRAIN-2DX computer program for non-linear analysis has been modified, by introduction in the beam-column elements (type 02) a generalised form of the yielding surface in the three-dimensional space of N-M-V internal forces. Non linear static analyses are performed following the prescription of the recent Italian code for construction on seismic areas (Ordinanza del Presidente del Consiglio dei Ministri n°3274). The numerical applications shown that, when framed structure characterized by a small ratio of the story height to cross section dimensions and low transversal reinforcements are considered, great reductions of the PGA of the seismic actions that produces the structure collapse (up to 45%) is obtained.

Effetti del interazione M-N-V nelle colonne in c.a. soggette ad azione sismica

RECUPERO, Antonino
2004-01-01

Abstract

When strong ground motion occurs, frame columns and bridge piers are often subjected at the same time to high axial forces (N), bending moments (M) and shear forces (V). The presence of high shear stresses reduces the structural element strength to combined actions of axial forces and bending moments, the deformation capacity, and the available ductility. Thus, a premature degradation of seismic performance of the structural elements and of the whole structure occurs. Different approaches can be followed for evaluation of N-M-V interaction effects under static or/and seismic actions. A first group is based on the extensions of the well-known formulation by Mörsh , following the indications given by experimental tests. An alternative approach has been furnished by Vecchio and Collins (1988), and involves a more complex procedure that is infeasible for technical applications. Let us stress that N-M-V interaction effects strongly influence the seismic performances of existing buildings that, in absence of seismic codes, have been designed with low transversal reinforcements, unable to give shear strength and confinement actions. In the present paper the influence of the N-M-V interaction on the reduction of the strength of frame beams and columns loaded by high axial force due to dead loads is analysed. To this aim, a model proposed in a recent paper, characterized by a variable slope of the stress fields in the core region of the reinforced concrete section is generalised, in order to be utilized for r.c. elements having rectangular cross sections subjected to seismic actions. The behaviour of elements having low transversal reinforcements for confining action and shear resistance are analysed by evaluation of three dimensional yielding surfaces that take into account the N-M-V interaction, showing that a great reduction of the bending capacities can be estimated. The model is employed for the evaluation of the influence of the N-M-V interaction on the seismic response by pushover analysis of an r.c. frame constructed in the late seventies, for which the mechanical properties of the construction materials have been evaluated by experimental tests. To this aims, the DRAIN-2DX computer program for non-linear analysis has been modified, by introduction in the beam-column elements (type 02) a generalised form of the yielding surface in the three-dimensional space of N-M-V internal forces. Non linear static analyses are performed following the prescription of the recent Italian code for construction on seismic areas (Ordinanza del Presidente del Consiglio dei Ministri n°3274). The numerical applications shown that, when framed structure characterized by a small ratio of the story height to cross section dimensions and low transversal reinforcements are considered, great reductions of the PGA of the seismic actions that produces the structure collapse (up to 45%) is obtained.
2004
9788886281980
File in questo prodotto:
Non ci sono file associati a questo prodotto.
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/1722674
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact