Implementation and finite-element analysis of shell elements confined by Through-The-Thickness uniaxial devices

This contribution presents the implementation in OpenSees of an integration procedure based on a recently developed theory concerning stress integration along the chords of a shell element reinforced with uniaxial transverse links. Such a model has been developed in order to account for transverse confinement effects induced by through-the-thickness jacketing of masonry and reinforced concrete existing structures. In particular, transverse confinement induces a triaxial stress state in the core material of the shell increasing the stress spherical part and resulting in strength and ductility increments. In order to perform structural analyses with reduced computational costs, the presented tool permits to compute the response of plane elements confined by uniaxial devices. To this end, the implemented object accounts for the mutual interaction of uniaxial reinforcements with a triaxial core by means of equilibrium and compatibility equations involving several object classes of the OpenSees framework. Integration of the triaxial stress state along the thickness of a shell element is therefore performed by numerically solving the equilibrium/compatibility equation system. The adopted implementation strategy is summarized and modeling features are discussed. In conclusion, numerical examples show some possible applications of the proposed tool in common structural design practices.