Keywords: steel portal frames, dynamic analysis, semi-rigid connections, column base plates, computational modelling, non-linear finite element analysis.

Traditionally, the steel portal frame design assumes that beam-to-column connections are rigid or pinned. Rigid connections, where no relative rotations occur between the connected members, transfer not only a significant amount of bending moments, but also shear and axial forces. On the other hand, pinned connections are characterized by almost free rotation movement between the elements connected that prevents the bending moment transmission. Despite these facts, it is largely recognized that the great majority of joints does not exhibit such idealized behavior. These connections are called semi-rigid, and their design should be performed according to their actual structural behavior.

Extensive research has been performed over the past twenty-five years to estimate the actual behavior of such joints. Numerous studies were published on composite and steel semi-rigid connections including: state of the art reports, numerical studies and experimental tests [1,2,3].

One of the main objectives of this work is to propose a modelling strategy to properly represent the semi-rigid joint response under dynamic loads. Another important issue investigated concerns the assessment of the structure dynamic behaviour due to the presence of symmetrical and non-symmetrical beam-to-column semi-rigid joints and, especially, the column base plates.

The mathematical model calibration was made through comparisons with tests and other numerical models found in the literature [3]. The structural analysis was made with the aid of the ANSYS [4] finite element program. The finite element model included geometric non-linearity, using an updated Lagrangean formulation, and considered the influence of non-linear and hysteretic moment versus rotation curve of the joint.

The results indicated that the resonance physical phenomenon was not reached in the nonlinear semi-rigid frames dynamic response. The resonance does not occur in these systems due to the hysteretic damping induced by the energy dissipation of the non-linear hysteretic loops at the non-linear joints. It was concluded that the hysteretic damping cannot be observed in simple linear stiffness joint models and emphasized the important damping character developed in non-linear hysteretic joints.

1

Castro R.A. de, "Modelagem Computacional de Ligações Semi-R'igidas e sua Influência na Resposta Dinâmica Não-Linear de Pórticos de Aço", MSc Dissertation (In Portuguese), Post-graduate Programme in Civil Engineering, State University of Rio de Janeiro, UERJ, Rio de Janeiro, Brazil, 2006.

2

Jaspart J.P., Vandegans D., "Application of the Component Method to Column Bases", Journal of Construction Steel Research, Vol. 48, pp 89-106, 1998. doi:10.1016/S0143-974X(98)90196-1

3

Chui P.P.T., Chan S.L., "Transient Response of Moment-Resistant Steel Frames with Flexible and Hysteretic Joints", Journal of Constructional Steel Research, Vol. 39, pp. 221-243, 1996. doi:10.1016/S0143-974X(96)00038-7

4

ANSYS, Swanson Analysis Systems, Inc., P.O. Box 65, Johnson Road, Houston, PA, 15342-0065, Version 10.0, Basic analysis procedures, 2nd edition, 2003.

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