The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finiteelement (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned tendons taking into account the reduction of the pre-stressing stress due to the steel relaxation. The pre-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) [1-3] whereas the stress relaxation of the steel is simulated using a viscoelastic model called Generalized Maxwell. A 3D FE model was used, where the nonlinear material behaviour and geometrical analysis based on incremental-iterative load methods were adopted. Validation by comparison with the analytic solution will be done for the case of a concrete beam with a parabolic pre-tensioned steel tendon embedded and some viscoelastic cases are performed in order to perceive the behaviour of the Generalized Maxwell model. Several examples are shown where the capabilities of the method on large scale structures are exhibited.

The construction of confined masonry buildings have become a good choice to meet the housing needs of low income families in big cities. Despite this, current building codes for such constructions, allows the use of highly simplified analysis techniques, that have hardly changed in the last 40 years. This paper is based on the numerical simulation, and emerges as the need to combine and improve existing technologies in the field of FEM (Finite Element Method) analysis for composite materials, to assess the overall structural behavior of reinforced concrete structures with masonry in-fills, and consequently, to support the derivation of rational rules for analysis and design purposes. So, through the use of a simple yet powerful shell FE (Finite Element), the state-of-the-art theories of mixtures to analyze composite materials, a computational tool to generate the volume fraction of composites, and a Mexican building code, this paper pretends to be a guidance to numerically reproduce the overall behavior of confined masonry structures.

In order to correctly predict the kinematics of complex structures, analysis using three-dimensional finite elements (3DFEs) seems to be the best alternative. However, simulation of large multi-layered structures with many plies can be unaffordable with 3DFEs because of the excessive computational cost, especially for non-linear materials. In addition, the discretization of very thin layers can lead to highly distorted FEs carrying numerical issues, therefore, reduced models arise as an affordable solution.\ud \ud This paper describes a new finite element formulation to perform numerical simulations of laminated reinforced concrete structures. The intention of this work is that the proposed scheme can be applied in the analysis of real-life structures where a high amount of computational resources are needed to fulfill the meshing requirements, hence the resulting formulation has to be a compromise between simplicity and efficiency.\ud \ud So that, the condensation of a dimension (thickness), mandatory to model three-dimensional structures with two-dimensional finite elements (2DFEs), leads to refer all layers contained within such FEs to a plane, which is typically named middle plane or geometrical plane, since its sole function is to serve as a geometrical reference. This work is based on the assumption that the geometrical plane has to be distinguished from a mechanical plane, which is where the resultant stiffness of all layers is contained. It is also assumed in this work that the mechanical plane changes its position due to non-linear response of the component materials.Peer ReviewedPostprint (author's final draft

The seismic behavior of a representative medium-rise building of Mexico City has been evaluated using the capacity spectrum method. This method is widely used nowadays in the seismic assessment of buildings, since it allows obtaining fragility curves which permit evaluating the ability of a building to resist earthquakes. A real full-height multi-story model is proposed to test the capabilities of the algorithm herein exhibited. The model is outlined through structural drawings; sized and structured following the building code regulations for masonry structures in Mexico City. Computational requirements for the analysis of large structures are indicated, in addition to the improvements to a non-linear computing code for a better performance in terms of memory management and execution times. 1 Escudero, September 23, 2019 Finally, a comparison between obtained results and the building code regulation is carried out, highlighting differences in the obtained results. The need to handle meshes with high amount of finite elements pushed us to develop a new layered finite element (FE), that can reproduce the non-linear behavior of its constituent materials when there are out-of-plane stresses without having to introduce additional degrees of freedom. The proposed FE has been compared with standard FE, presenting different kinematics, and excellent results have been obtained. This work emerges as the need to combine and improve existing technologies in the field of finite element analysis. One of such technologies is the numerical simulation of the behaviour of composite materials. That is why it has also been necessary to develop a computing program capable of reading both finite element meshes and patterns of fibers represented with convex polygons, and as a result of areas intersections between polygons returns volumetric participation of fiber and matrix of constituents materials for each layer, in addition had to return the fiber orientation with respect to the local axis of the finite element.