Nonlinear analysis in FTOOL with semi-rigid connections: a partial development

Resumo

FTOOL is an interactive graphic software used worldwide by students and engineers for analysis of
two-dimensional frame models. The main objective of this work is to present the partial development of a new
version of FTOOL, incorporating semi-rigid connections in the analysis. The new version simulates a semi-rigid
connection by inserting a rotational spring finite element with linear-elastic or nonlinear behavior, allowing a
physically nonlinear analysis. An important characteristic of this implementation is that the stiffness matrix of a
connection finite element is not condensed to the beam element that contains the join, as it is usually done. Instead,
a fictitious node with only one additional rotational degree of freedom is created for each semi-rigid connection in
the planar case. The advantages of this approach are that the physically nonlinear behavior is isolated from the
elastic behavior of the beam elements and that the stiffness matrix of a nonlinear connection fictitious element is
assembled to the global stiffness matrix independently. The numerical algorithms to compute the nonlinear
solution of the structure are based on a geometric nonlinear analysis implementation of FTOOL, adapted to
physically nonlinear analysis. The resulting version will incorporate geometric and physical (from semi-rigid
connections) nonlinear analyses.