Numerical analysis of concrete-filled tubes with stiffening plates under large deformation axial loading
- Autores: Albert Albareda Valls
- Directores de la Tesis: Jordi Maristany i Carreras (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2013
- Idioma: inglés
- Tribunal Calificador de la Tesis: Frederic Marimón Carvajal (presid.), Lluís Moya Ferrer (secret.), Enrique González Valle (voc.), Fructuoso Maña Reixach (voc.), Manuel Luis Romero García (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Concrete-filled tubes have been increasingly used these recent decades thanks to their improved structural behavior, especially under compression.Concrete filling in these sections improves ¡ts compressive strength thanks to lateral pressure coming from confinement effect provided by the steel tube. At elevated percentages of loading,concrete suffers an important volumetric expansion, which is clearly restricted by the tube. Therefore, the core is subjected to a severe lateral pressure that clearly enhances the compressive response of the concrete filling. This advantageous response under compression is accompanied by a significant ductility and energy absorption, owing to crushing of the cement paste of concrete. The core is subjected to asevere damage process, while mast part of the axial load is still resisted until advanced stages of deformation, thanks to be contained by the tube. These two properties let concrete-filled tubes to play an important role in the construction of really tall buildings in seismic areas. However, confinement effect on the core and the absorption of energy in these sections is clearly different between circular and square-shaped tubes. While in circulartubes, laleral pressure over the core is clearly uniform and constant, in square-shaped tubes, the deformability of the plates implies a notorious reduction of these two mechanical capabilities. This fact can be partially solved by means of introducing stiffening plates in the core. Thus, main purpose of this investigation is to analyze and describe the influence of introducing these plates in the core of concrete-filled tubes; also the influence on circular sections is analyzed in the study. The presence of stiffening plates not only has a clear effect on the confinement effect on the core, but also on the ductility of the section. In square-shaped sections this effect is always positive,independently of the thickness of the plates and the width ofthe section; nevertheless, in circular tubes, their influence is not so significant or even negative, since circular geometry is much more effective than a cruciform shape, in terms of confinement and ductility. ln otherwords, the introduction of stiffening plates in circular concrete-filled tubes is always positive, provided that the presence of these plates does not leadn to consider thinner tubes. The proposal of concrete-filled tubes stiffened with plates, or "reticulated" concrete-filled tubes, is interesting from several points of view. These new embedded plates are normally restricted to buckling by the concrete filling, so that they could be fully loaded according to their plastic capacity, being also protected against fire. The introduction of a couple of plales in the core of these tubes not only enhances the confinement effect and ductility, but also it allows a safer response against fire. The cruciform or grid-shaped geometry is interesting also for an excellent behavior under combined states of compression with shear forces or bending -the first case corresponds exactly to those heavily loaded columns of the ground fioors in tall buildings. What is a solution with a clear structural vocation derives quickly into a new interesting sectional repertoire for designers, by analyzing the load-bearing capacity of each independent loading cell of reticulated sections and combining them in different ways. The possibility of analyzing these cells separately allows determining their compressive response depending on their location in the cross-sectional plane and on the proportion between their width and plate thickness .
