Alexandre Rodrigues Pacheco

Modelo 3D de elementos finitos para análise de estruturas de concreto armado

This work presents a numerical model for 3D analyses through the finite element method of reinforced concrete structures subjected to monotonic loads. The proposed model for concrete is orthotropic and uses the equivalent uniaxial strain concept. The equivalent uniaxial stress-strain relation is generalized to take into account the triaxial stress conditions. The parameters used in the equivalent uniaxial stress-strain curve are determined from the failure surface defined in the principal stress space. The implementation in finite elements is based on the consideration of smeared cracks with cracks rotating according to the directions of the principal stresses. Also, an embedded reinforcement model was implemented to represent existent reinforcing bars. Finally, some results are compared with experimental data from the literature to demonstrate the validity of the numerical model developed.

Revisions to Accelerated Corrosion Test Method for Post-Tensioning Grout

A minimum degree of corrosion protection should be conferred to an embedded prestressing strand by post-tensioning grouts, along with placement-related requirements. The accelerated corrosion test (ACT), an anodic polarization test procedure, is currently used to measure corrosion protection in the United States. Approval of a specific grout currently requires two conditions: a 1,000 hour average ACT time-to-corrosion minimum result; and a 0.45 water-cement ratio standard mixture (only water and portland cement) less than or equal to an ACT time-to-corrosion result tested under the same conditions. Different combinations of the two approval conditions are used in various specifications. Criticism has resulted since the ACT test procedure does not currently require that grout resistance variations be accounted for during selection of applied voltage. The addition of admixtures and pozzolans can significantly vary grout resistance, perhaps affecting test results adversely. The authors report on research on different ACT test post-tensioning grout mixtures with admixture level variation and resistivity effects inherent to electrochemical systems compensation option. Study results show that resistivity variation significantly affected test type variation, so when testing equipment does not allow IR compensation, potentially lower quality grouts may occur.

Linear Polarization Resistance Tests on Corrosion Protection Degree of Post-Tensioning Grouts

This article discusses the current industry practice for acceptance testing of post-tensioning grouts. The practice includes an accelerated corrosion test (ACT), as recommended in Post-Tensioning Institute (PTI) M55.1-03, “Specification for Grouting of Post-Tensioned Structures.” The current ACT method typically takes 1 to 2 months to complete and is seen as a downside. However, the linear polarization resistance (LPR) technique requires only a few hours to complete. The research presented in this paper indicates a strong correlation between the time to corrosion, as measured by the ACT method, and the system polarization resistance, as measured by the LPR technique. The authors recommend the use of the LPR method as a prescreen for very high-quality grouts so that lengthy ACT testing is not necessary.

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.

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.