Álvaro F. M. Azevedo

A direct method for analyzing the vertical vehicle-structure interaction

Article history: Received 24 June 2011 Revised 24 September 2011 Accepted 3 October 2011 Available online 10 November 2011

Numerical Simulation of Thin Steel FiberSelf-Compacting Concrete Structures

Fundacao para a Ciencia e a Tecnologia (FCT) - POCTI/ECM/57518/2004 “FICOFIRE - High performance fiber reinforced concrete of enhanced fire resistance”, bolsa de doutouramento SFRH/BD/23326/2005.

A nonlinear vehicle-structure interaction methodology with wheel-rail detachment and reattachment

. A vehicle-structure interaction methodology with a nonlinear contact formulation based on contact and target elements has been developed. To solve the dynamic equations of motion, an incremental formulation has been used due to the nonlinear nature of the contact mechanics, while a procedure based on the Lagrange multiplier method imposes the contact constraint equations when contact occurs. The system of nonlinear equations is solved by an efficient block factorization solver that reorders the system matrix and isolates the nonlinear terms that belong to the contact elements or to other nonlinear elements that may be incorporated in the model. Such procedure avoids multiple unnecessary factorizations of the linear terms during each Newton iteration, making the formulation efficient and computationally attractive. A numerical example has been carried out to validate the accuracy and efficiency of the present methodology. The obtained results have shown a good agreement with the results obtained with the commercial finite element software ANSYS

Thermo-mechanical model for the material nonlinear analysis of cement based materials

Financial support of FCT, PhD Grant number SFRH/BD/23326/2005. The authors acknowledge the support provided by SUPERCONCRETE Marie Sklodowska-Curie Actions, Research and Innovation Staff Exchange (RISE), proposal 645704

Object Oriented Implementation Of A Second-order Optimization Method

A structural optimization problem may be formulated as a single nonlinear program (NLP) and solved with a second-order method. This class of methods requires first and second derivatives of the objective function and of the inequality and equality constraints. When the size of the problem is large, derivative calculation may become tedious and error prone. Automatic differentiation (AD) techniques provide exact values for the derivatives without user intervention. In this paper the object oriented implementation of a Lagrange-Newton optimization algorithm is presented. An object oriented parser is used to interpret all the functions that describe the NLP. First and second derivatives are calculated with AD techniques using Rall numbers and their associated overloaded operators. A shape optimization example is presented to illustrate the proposed techniques.

Second-order Optimization Of Frames WithNonlinear Behavior

In this paper an integrated formulation for the structural optimization of frames with nonlinear material behavior is presented. Member sizes, generalized displacements and internal forces are treated as variables of the nonlinear program. The objective function is the cost of the structure. Equilibrium equations and plastic hinge complementary conditions are treated as equality constraints. Stresses, displacements and plastic hinge rotations may be limited. Plastic hinges are automatically located in the most critical position. The nonlinear program is solved by a second-order Lagrange-Newton algorithm. The computer implementation parses all the expressions and calculates first and second derivatives of the Lagrangian. The sparsity of the Hessian matrix is taken into account and several numerical techniques are used to improve the efficiency and the reliability of the optimization process. A numerical example is presented.