Anna Saetta

Analysis of Chloride Diffusion into Partially Saturated Concrete

This paper describes the governing equations of moisture, heat, and chloride ion flows through concrete within the framework of a distributed parameter model. The coupling terms and the nonlinearity of the problems are taken into account and a numerical procedure based on the finite element method is developed to solve the set of equations. This study examined chloride diffusion even in partially saturated concrete by considering the variability of ion diffusion coefficients with concrete parameters. Chloride intrusion in various environmental conditions was investigated and the effect of moisture flux in transporting dissolved ions through the porous media is considered. Comparisons with experimental tests are also carried out to show the reliability and the effectiveness of the proposed numerical model.

THE CARBONATION OF CONCRETE AND THE MECHANISM OF MOISTURE, HEAT AND CARBON DIOXIDE FLOW THROUGH POROUS MATERIALS

Abstract The governing equations of moisture, heat and carbon dioxide flows through concrete within the framework of a distributed parameter model are described. The coupling terms and the non-linearity of the problem are taken into account and a numerical procedure based on the finite element method is developed to solve the set of equations. The influence of relative humidity and temperature is investigated and typical results are presented. Comparisons with experimental tests are also carried out and one example is presented in detail in order to show the reliability and the effectiveness of the proposed numerical model.

2 — D model for carbonation and moisture/heat flow in porous materials

The previously-published one-dimensional finite element model for the analysis of the carbonation mechanism is extended to two-dimensional problems. The governing equations for the propagation of aggressive agents through concrete are rewritten for two-dimensional domains. A comparison is made with the one-dimensional model and some examples are developed to test the method. Finally, the study of a reinforcing bar placed at the comer of a concrete structure is presented in detail to show that the proposed numerical model is able to demonstrate the effects of the multidimensional moisture, heat and carbon dioxide transport through concrete.

A scalar damage model with a shear retention factor for the analysis of reinforced concrete structures: theory and validation

Abstract A local isotropic single parameter scalar model that can simulate the mechanical behaviour of quasi-brittle materials, such as concrete, is described. The constitutive law needs the mechanical characteristics and the fracture energy of concrete to be completely defined. The damage parameter is obtained directly from the value of an equivalent effective stress in order to reduce the computing effort. Due to the unique damage parameter, this model is suitable for the study of quasi-static problems involving monotonically increasing loads. The problem of localisation and mesh dependency have been partially overcome by using an enhanced local method in which a characteristic internal length related to the mesh dimension is employed instead of the characteristic fracture length. In this work, the model was enriched further with the introduction of a shear retention factor that accounts for the friction between the two surfaces of a crack. These new features assure a real improvement of the damage model, maintaining nevertheless its simplicity and low computing cost and making it suitable for the practical solution of large scale problems. Several numerical simulations of experimental tests, concerning fracture tests on concrete specimens and beams failing in shear, have been performed for the validation of the model. The main results from the numerical analyses are described and compared with the experimental ones.

Non-linear dynamic analysis of cable-suspended structures subjected to wind actions

Abstract The numerical analysis of the response of wind-loaded flexible structures is presented. Initially the modeling and simulation of wind velocity are studied, by considering stationary, multivariate stochastic process, according to its prescribed cross-spectral density matrix. In the second part of the paper, geometrically non-linear structures subjected to wind loads are investigated, by means of a finite element approach. One test example is presented to show the reliability of the numerical procedure to solve geometrically non-linear problem in dynamic field. Finally, the study of a real structure characterized by an initial pre-tension layer subject to wind action is carried out.

On the stability and instability regions of non-conservative continuous system under partially follower forces

Abstract The transition between stability and instability of a uniform cantilever beam subjected to a partially follower load is discussed by means of the finite element method. The stability diagram in terms of the load versus the non-conservativeness loading parameter is obtained both in the hypothesis of linearized (small displacements) and non-linearized (large displacements) analysis. It is found that the regions of divergence and flutter instability of the finite element model of continuous system are quite different from the corresponding ones obtained for the classical 2 degrees of freedom Zieglers model (i.e. the inverted double pendulum), both quantitatively and qualitatively. The transition from the 2 degrees of freedom model to the continuous model is investigated through the study of some multi degrees of freedom approximation models (i.e. the 3, 4, 5 and 10 degrees of freedom models) of the continuous column. Finally, the effect of damping in the stability diagram of the finite element model of continuous system is discussed and the destabilizing effect of small damping is emphasized.

Finite element solution of the stability problem for nonlinear undamped and damped systems under nonconservative loading

A nonlinear finite element analysis of elastic structures which can be studied by a 3D beam theory, subjected to conservative as well as to nonconservative forces, is presented. The stability behaviour of the system is studied by means of an eigenvalue analysis. The stiffness matrix of the eigenvalue problem is asymmetric (i.e., non-self-adjoint system). The flutter and divergence modes of instability, as well as the values of the critical load, are identified for a number of numerical examples belonging to the benchmark tests proposed by NAFEMS (1990). The results demonstrate the reliability of this finite element formulation. In particular the effect of damping on the stability behaviour of such structures is investigated and the destabilizing effect of small damping is underlined. Finally, the need to define a number of benchmark tests for nonlinear-nonconservative analyses in presence of damping is included.

Dynamic behavior of a tensegrity system subjected to follower wind loading

Abstract The aim of this paper is to present a possible develop-line for the study of large lightweight roof structures by non-linear geometric analysis, under the dynamic effects of the turbulent action of the wind, that can be applied into the classical engineering applications. In particular the paper deals with the study of tensegrity systems, that can be defined as pattern that results when push (struts) and pull (tendons) have a win–win relationship with each other. The pull is continuous and the push is discontinuous. The continuous pull is balanced by the discontinuous push producing an integrity of tension–compression. Static and dynamic analyses of the wind action effects on one example of such tensegrity system, i.e. the roof over the La Plata stadium, Argentina, have been performed by using the geometrically non-linear FE procedure named “Loki”. The wind loads are simulated as deformation-dependent forces. Both experimental data and numerical results available from the roof designers, have permitted to control the reliability of the proposed mathematical model.

Seismic risk mitigation technique for art objects: experimental evaluation and numerical modelling of double concave curved surface sliders

The opportunity and the advantages of applying base isolation technologies developed for civil structures to small objects are investigated and some considerations related to the scale effects are discussed. A series of experimental tests carried out at SRMD facility in San Diego are presented with the aim to investigate the dynamic response of a system designed to simulate a sculpture isolated by means of Double Concave Curved Surface Sliders. Such devices are specifically re-designed to fit the peculiar situation of light weight objects. In particular the samples used in the experimentation are designed with geometric and inertia characteristics fit for representing the Michelangelo’s sculptures exposed at the “Galleria dell’Accademia” in Florence, Italy. Finally, the main aspects concerning the numerical simulation of the seismic response of the proposed isolated system are discussed, also to investigate the efficiency of the existing numerical models, which are developed for traditional devices, when they are applied on such small and particular objects. The results of the experimental/numerical campaign show a general efficiency of the isolation system in terms of limiting the transferred action. Further study is needed to understand more clearly some local unexpected phenomena emerged from the experimental tests.

A non-linear finite element formulation for shells of arbitrary geometry

Abstract Based on a total Lagrangian approach, the shell element formulation developed by two of the authors is extended to non-linear field. The proposed shell element belongs to the degenerated 3D type, with a Mindlin–Reissner approach and five effective degrees of freedom per node. A detailed description of the geometry and kinematics characterisation of the element, as well as of the stress–strain relationship is presented. Numerical testing of the non-linear model indicates excellent performance of the proposed finite element shell, both in simulating large displacement and rotations, and in the buckling analysis of some classical test examples, e.g., cylinder and sphere.