Failure Mode Control of steel MR-Frames with pin-jointed column bases - F8

The promotion of a collapse mechanism of global type is of primary importance in earthquake resistant design, because partial and local failure modes are responsible of the worsening of the energy dissipation capacity leading to an increased risk of collapse under destructive seismic events. Therefore, dissipative zones have to be located at the beam ends whereas column sections, which constitute the unknown of the design problem, need to remain in elastic range. To this scope, the theory of plastic mechanism control can be applied. It also includes the influence of second order effects which are accounted for by means of the concept of mechanism equilibrium curve. The design requirements are derived by means of the kinematic theorem of plastic collapse. Column sections are obtained by imposing that the mechanism equilibrium curve corresponding to the global mechanism has to lie below those corresponding to all the other undesired mechanisms within a displacement range compatible with the local ductility supply. This theory is herein presented with reference to MR-Frames with pin-jointed column bases. The case of pin-jointed column bases is very interesting from the practical point of view, because it can be demonstrated that the obtained structural solution is also a safe side solution in case of MR-Frames with fully restrained column bases. Aiming at the evaluation of the accuracy of the presented procedure, push-over analyses are carried out to investigate the actual collapse mechanism typology of MR-Frames designed according to the proposed method.

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