Insight into the structural behavior of concrete hinges by means of Finite Element simulations

Abstract

Concrete hinges experience a renaissance, because the past decades have provided practical evidence that they are durable structural elements, but the functionality of concrete hinges remains to a considerable extent an enigma. This provides the motivation to gain further insight into the structural behavior of concrete hinges, based on nowadaysavailable experimental and theoretical methods. The present master thesis focuses on the numerical re-analysis of recently performed centric and eccentric compression tests on concrete hinges, based on nonlinear Finite Element (FE) simulations carried out with concrete model -CC3DNonLinCementitious2- and the software Atena science 5.1. FE simulations based on default material parameters, related to the measured Young-s modulus and to the measured cube compressive strength of concrete, significantly overestimate the experimentally observed structural stiffness and ultimate load carrying capacity of concrete hinges. Consideration of concrete shrinkage and of a more moderate strengthening of concrete under triaxial compression allows for a qualitatively and quantitatively satisfactory reproduction of experimental measurements. In addition, a recently developed multiscale model for tensile strength and softening of concrete is used to quantify damage of concrete resulting from shrinkage strains restrained by the two connected reinforcement cages. The FE simulations underline that concrete hinges exhibit a structural behavior which is very beneficial for structural applications. Close to the ultimate load carrying capacity, rotation angles increase significantly, while the strength of the structure is almost constant. This results from the rather ductile behavior of concrete forming the surface at the innermost region of the neck, where a biaxial compressive stress state prevails. Only because this concrete surface layer remains in place (no spalling), a triaxial compressive stress state can build up behind the surface layer, i. e. inside the volume of the neck. The resulting confinement pressure increases the strength of concrete considerably, and this explains the unexpected large load carrying capacity of concrete hinges.