Abstract When exposed to high temperatures, such as in a fire situation, the physical and resistance characteristics of the materials employed in the structure deteriorate as the temperature increases. This fact promotes a considerable loss in the bearing capacity and stiffness of the structural system. The verification of a structure exposed to fire depends primarily and principally on the thermal analysis of the cross section of the structural element. This analysis permits determination of the temperature variation or temperature range in the element from the boundary conditions provided by the fire model adopted. As such, this study had the objective of performing a thermal analysis in a transient regime by means of a finite element method on steel-concrete composite cross sections that are employed in civil construction through use of the Computational System for Advanced Structural Analysis/Fire Analysis (CS-ASA/FA). Two cross sections are analyzed and the results obtained were satisfactory. In addition, different iterative solution processes were adopted in the analysis. Parametric studies were also performed related to the mesh variation of the finite elements and time increase. From the results, it was possible to conclude that CS-ASA/FA can supply the necessary information when a thermo-structural analysis is performed for the evaluation of strength and stiffness losses of the structural material when exposed to fire.

Grande parte dos procedimentos numéricos para obtenção de caminhos de equilíbrio dos problemas estruturais com comportamento estático não linear baseia-se no método de Newton-Raphson, ao qual são acoplados métodos de continuação. Nesse contexto, esse trabalho usa uma técnica, referida como fluxo normal, no processo de obtenção da resposta aproximada não linear estática de sistemas estruturais. Tal técnica trata-se, basicamente, de uma modificação estabelecida no esquema iterativo de Newton-Raphson, na tentativa de acelerar o processo de solução e/ou contornar problemas de convergência. Para ultrapassar os pontos limites e traçar a trajetória de equilíbrio completa das estruturas, adotam-se três diferentes estratégias de iteração: comprimento de arco, norma mínima dos deslocamentos residuais e deslocamento generalizado. Com esse procedimento, é avaliado o desempenho dessas estratégias, quando associadas à técnica do fluxo normal. Dois arcos com caminhos de equilíbrio não lineares são usados no estudo. Os resultados encontrados permitem concluir que a associação da estratégia do deslocamento generalizado com a técnica do fluxo normal contribui para a eficiência da metodologia de solução não linear.

A large part of the numerical procedures for obtaining the equilibrium path or load-displacement curve of structural problems with static nonlinear behavior is based on the Newton-Raphson iterative scheme to which are coupled the path-following methods. In this context, this study uses one technique, referred to as normal flow, in the process of obtaining the approximate nonlinear static response of structural systems. Basically, this technique is an adaptation made with in the Newton-Raphson iterative scheme in an attempt to speed up the nonlinear solution process and/or remove convergence problems. To overcome the critical points and to trace the whole nonlinear equilibrium path, three different strategies are used in association with the normal flow technique: the cylindrical arc-length, the minimum residual displacement norm and the generalized displacement. With this procedure, the performance of these strategies when associated with the normal flow technique is valued. Two arches with highly nonlinear load-displacement curves are used in the study. The results obtained demonstrated that the association of the generalized displacement strategy with the normal flow technique contributes to the improvement of the nonlinear solution methodology.