Rodolfo Danesi

Experimental and computational analysis of plates under air blast loading

The main objective of this paper is the comparison between testing and numerical responses of metallic plates subjected to explosive loads, in order to obtain guides to the numerical modeling and analysis of this phenomenon. Moreover, the secondary objective was to provide data that could be used for checking the accuracy of a variety of calculation methods. A set of four tests at natural scale is presented on two nonstiffened metallic steel plates with different boundary conditions (one clamped in the soil and another clamped in the four edges), subjected to the action of pressure waves originated by the detonation of explosive loads. The time history of the acceleration in different points of both plates and the pressure waves in selected points, are recorded. On the other hand, a linear dynamic analysis of the plate models with the code ABAQUS was carried out. The influence of the number of natural modes that are considered for the analysis and the refinement of the mesh are analyzed. Moreover, a nonlinear geometric analysis was carried out in order to verify this possible behavior in the first plate. Suggestions to computational modeling of structures under impulsive loads arise from the comparison of numerical and experimental results.

Coupled plastic-damaged model

Abstract A constitutive model that couples plasticity and damage is presented. The model is thermodynamically consistent and comes from a generalization of classical plasticity theory and isotropic damage theory of Kachanov. Coupling between plasticity and damage is achieved through a simultaneous solution of the plastic and the damage problem. After a description of the model, a numerical algorithm for the integration of the resulting constitutive equations is presented. It is an Euler Backward type of algorithm that is particularly suitable to solve plain stress non-linear problems with a 2D finite element program. The consistent stiffness matrix is also derived. The paper is completed with some application examples that show that the model presented accurately reproduces the behaviour of elastic-plastic-damaged materials.

Thermo-mechanic model for concrete exposed to elevated temperatures

Abstract A thermo-mechanical model for concrete subjected to high temperatures is presented in this paper. The model is based on a coupled plastic-damage model that has been extended to consider damage induced by high temperatures. The model is calibrated with experimental results of residual strength tests in concrete specimens. The paper is completed with application examples and comparisons with experimental results that validate the model presented. The model is also used to the damage assessment of a concrete structure that has been subjected to fire.

A modified Vlasov theory for dynamic analysis of thin-walled and variable open section beams

The equations of motion of thin-walled beams with open cross-section considering the effects of shear flexibility, rotatory inertia in the stress resultants and variable cross-sectional properties are presented. These equations are based on Vlasovs theory of thin-walled beams, which is modified to include the effects indicated above. The formulation is also applicable to solid beams, constituting therefore a general theory of coupled flexure and torsion of straight beams. The differential equations are shown to be particularly suitable for analysis in the frequency domain using a state variables approach. The resulting equations are used in the determination of the natural frequencies and the seismic response of a building provided with a thin-walled reinforced concrete core to resist lateral loads. Finally, an example of a variable section channel beam is presented, which provides additional evidence on the generality of the formulation.

Time-Dependent Analysis of Reinforced andPrestressed Concrete Members

A new step-by-step method is proposed that allows the determination of the history of strain and stress distribution in concrete sections with prestressed and nonprestressed reinforcement. It considers time-dependent effects on concrete and prestressed steel independently of the cracked or uncracked state. The analysis is performed at different time intervals satisfying the strain compatibility between concrete and all layers of steel, as well as the equilibrium equations in sections subjected to normal forces and moments due to external loads. The development along the time of the creep coefficient, shrinkage, and relaxation loss is taken into account on the basis of prediction models and equations that may be extracted from codes and recommendations. Numerical examples in reinforced, prestressed, and partially prestressed concrete sections, including different loading conditions, are used to demonstrate the applicability of the proposed method.

Analysis of structures subjected to random wind loading by simulation in the frequency domain

Abstract The closely related methods of transfer matrices and direct numerical integration have been extensively used in the analysis of free standing structures. In case of structures subjected to dynamic loading, the method is particularly suitable to analysis in the frequency domain, enabling the consideration of arbitrary linear time-dependent material behaviour without additional difficulties. In this paper, a method is proposed to simulate stationary random processes in the frequency domain and it is applied for analysis of structures under along-wind action. The method requires less computational effort than standard procedures to obtain the power spectral density function of response quantities of interest and, since the solutions are obtained by simulation, may be extended to include in the formulation some types of non-linearity. Furthermore, it can be advantageously employed in the dynamic analysis of thin-walled open section beams, for which other alternatives are rarely available. The method proposed is applied to various free-standing towers and chimneys, for which response measurements are available, allowing a direct comparison of theoretical and experimental results.

On the influence of foundation flexibility on the seismic response of structures

Abstract The main objective of this paper is to contribute to a quantification of the effect of foundation flexibility on the most important design variables in the seismic response of building structures with prismatic rectangular foundations. A soil–structure interaction model was used for this purpose. A general continuum formulation was adopted to represent the physical model of the structure and a lumped parameter model was adopted to represent the soil and the interaction mechanisms. Using the implemented models and in view of the objective of the work, a parametric study was made. For this purpose, a group of three structures, three seismic accelerations and seven sets of soil properties will be considered. The results obtained, in view of the large number of uncertainties involved, are presented in a probabilistic format and suggest that the soil–structure interaction can be neglected in the analysis of this class of structures.

Determinación de cargas generadas por explosiones en ambientes urbanos

El objetivo principal de este trabajo es la determinacion de la masa de explosivo y la ubicacion del foco de la explosion generada por un ataque terrorista en un ambiente urbano congestionado. La metodologia presentada es especialmente util cuando las dimensiones del crater generado por la explosion son inciertas o desconocidas. Se realizo un analisis computacional para la determinacion de presiones e impulsos en las fachadas de los edificios de una cuadra en un ambiente urbano real. Se realizaron simulaciones correspondientes a diferentes combinaciones de masa de explosivo - ubicacion del foco. Por otra parte, se realizo la evaluacion del dano producido en los edificios a traves de la utilizacion de las curvas de isodano que relacionan, en forma aproximada, las presiones e impulsos con los danos producidos. Posteriormente se definieron contornos de igual dano y se trazaron los mapas de isodano en toda la cuadra, para las diferentes alternativas analizadas. Por ultimo, a traves de la comparacion de los danos reales y los simulados computacionalmente, pudieron descartarse las alternativas no coincidentes.