NONLINEAR ELASTIC TRANSIENT ANALYSIS OF STEEL FRAMES WITH SEMI-RIGID CONNECTIONS

Resumo

Steel structures are reputed to have high slender ratio and excellent ductility. Due to these
features, the second-order effects and the influence of connection flexibility can play an important role
on the behavior of such structures since they can increase the risk of instability. Additionally, it has been
observed that only the linear static analysis may not describe the real behavior of a structure submitted
to various external requests, especially in the case of atypical situations, such as earthquakes and strong
wind gusts. Thus, the aim of this research is to evaluate the repercussion of the geometrical nonlinearity
and connection flexibility on the transient elastic response of plane steel frames. To this end, it is
employed a geometrically exact nonlinear formulation, based on Euler-Bernoulli model, that considers
the updated Lagrangian formulation and the corotational approach for the consistent deduction of the
element’s tangent stiffness matrix. The theory predicts that nodes will suffer large displacements and
rotations, and the elements of the structure, large stretches and curvatures. The semi-rigid connection is

modelled by a rotational spring element whose behavior is obtained on the basis of a bilinear moment-
rotation diagram that follows the kinematic hardening rule. In order to solve the nonlinear transient

equations, it is adopted the Newmark’s implicit time integration method combined with the Newton-
Raphson technique. The results of the performed analyzes showed a good agreement with the numerical

solutions available in the literature, demonstrating the efficiency of the proposed method in obtaining
the geometrically nonlinear dynamic response of steel structures with semi-rigid connections.