Américo Campos Filho

Response variability in reinforced concrete structures with uncertain geometrical and material properties

Abstract This paper presents a model for probabilistic analysis of reinforced concrete structures. The study considers the effects of structural geometric imperfections, as well as the materials’ mechanical properties variability on the response of beams and columns. The finite element method is combined with the Monte Carlo simulation method. The parameters of the analysis are represented as either random variables or as stochastic fields. After several simulations, the expected values and standard deviations of the deflections and of the rupture loads are evaluated. Finally, the variability of the response of the structure is investigated.

Numerical analysis of reinforced concrete beams strengthened with high strength cement-based composite material

A aplicacao de materiais compositos a base de resinas polimericas e fibras no reforco de estruturas de concreto armado se tornou uma tecnica bastante difundida nos ultimos tempos. O uso dos compositos reforcados com fibras de carbono, ou outros tipos de fibras sinteticas, se consolidou pelas suas excelentes caracteristicas, tais como elevada resistencia, baixo peso, resistencia a corrosao, etc. Este material, na forma de lâminas ou laminados, e colado no substrato de concreto atraves de adesivos a base de epoxi. Apesar do uso do epoxi apresentar excelentes resultados em termos de colagem e resistencia, algumas desvantagens podem ser citadas, tais como: baixa permeabilidade, baixa compatibilidade termica em relacao ao concreto, baixa resistencia ao fogo, etc. Para evitar alguns desses problemas, um sistema composito a base de tecidos ou malhas de fibras sinteticas coladas na superficie de concreto com argamassa de cimento pode ser usado. O objetivo deste trabalho e fazer uma analise numerica, atraves de um modelo nao linear de elementos finitos, do comportamento estrutural de vigas de concreto armado reforcadas a flexao com compositos baseados na combinacao de tecidos de fibras sinteticas de alta resistencia e argamassa de cimento. Os resultados numericos sao comparados aos resultados experimentais publicados em artigos tecnicos internacionais, que demonstram a eficiencia da tecnica de reforco e a capacidade do modelo numerico.

USO DE ARMADURA INCORPORADA NO ANSYS CUSTOMIZADO PARA A ANÁLISE DE VIGAS EM CONCRETO ARMADO

This work presents the development of a computational model, based on the finite element method, through the ANSYS platform, for the study of reinforced concrete structures, under plane stress states. The ultimate goal of this work is to implement two different procedures in the computational model that are based on an elasto-viscoplastic model. In the first procedure, the response of the structure is given for an instantaneous loading, considering the material with an elastoplastic behavior. In the second one, the response is given over time, considering the material as having a viscoelastic behavior. The representation of the constitutive equations of concrete and steel is carried out through a new model with the help of the customization tool UPF (User Programmable Features) of ANSYS, where new subroutines were added to the main program in FORTRAN language. The implementation of this new model enabled the use of two-dimensional eight-node quadratic elements (PLANE183) with embedded reinforcement elements (REINF263), making the solution of the problem faster and more effective. In order to validate the subroutines added to the system, the reinforced concrete beams tested by Bresler and Scordelis (1963), which cover a wide variety of structural behaviors, were modeled and analyzed with the procedures proposed. The comparison between experimental and numerical analysis showed a good adherence between results.

Using element-embedded rebar model in ANSYS for the study of reinforced and prestressed concrete structures

ANSYS is a software well accepted by professionals and academics, since it provides a variety of finite elements, material constitutive models, and linear and nonlinear analysis of structures in general. For the concrete material, for instance, the software uses an elastoplastic model with the Willam-Warnke surface of rupture (1975). However, this model is only available for finite elements that do not offer the possibility of use of the element-embedded model for rebars, demanding a much larger amount of elements to discretize structures, making numerical solutions less efficient. This study is, therefore, about the development of a computational model using the Finite Element Method via ANSYS platform for nonlinear analysis of reinforced and prestressed concrete beams under plane stress states. The most significant advantage of this implementation is the possibility of using the element-embedded rebar model in ANSYS with its 2D eight-node quadratic element PLANE183 for discretization of the concrete together with element REINF263 for discretization of rebars, stirrups, and cables, making the solutions faster and more efficient. For representation of the constitutive equations of the steel and the concrete, a proposed model was implemented with the help of the UPF customization tool (User Programmable Features) of ANSYS, where new subroutines written in FORTRAN were attached to the main program. The numerical results are compared with experimental values available in the technical literature to validate the proposed model, with satisfactory results being found.

A tridimensional finite element approach to model a tunnel with shotcrete and precast concrete

This paper describes a numerical simulation with 3D finite elements of a tunnel. The viscoplastic law of Perzyna represents the rockmass behavior. The concrete, shotcrete or precast, is modeled as a viscoelastic material through the Maxwell and Kelvin chain models. Finite element simulations are performed by incorporating subroutines for viscoelastic concrete models in the ANSYS code. The method to simulate tunnel excavations is by activating and deactivating elements in sequential steps. In the first part of the paper two validations are performed. The analytical solution and the deformation achieved on the stabilization in the ANSYS code are compared with an unlined tunnel. A lined tunnel, with an elastic and viscoplastic rockmass combined with an elastic lining, is compared with the results of the GEOMEC91 code. In the second part, it is compared the same tunnel with two different concrete lining for two chain models. Finally, it is modeled the Kielder experimental tunnel, which in situ measured data is available.

Finite element analysis of segmental concrete bridges

The application of externally post-tensioned segmental members is a very attractive solution compared with classical construction methods. The use of this solution results in smaller precast elements tied together by post-tensioned tendons, upbringing such advantages as fast and versatile construction, high quality control and lower overall cost. In this paper, a formulation based on the Finite Element Method is discussed. This formulation is used to numerically simulate the structural behavior of members composed of externally post-tensioned segments. These analyses not only allow serviceability limit states verifications when sections are fully compressed, but also allow verifications of ultimate limit states when joint openings and load transfers at the joints are considered. Additionally, to evaluate the accuracy of the numerical results of the computational model a comparison to experimental data from the literature is performed.