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Earthquakes and Structures
  Volume 16, Number 4, April 2019, pages 469-485

Ductility demands and reduction factors for 3D steel structures with pinned and semi-rigid connections
Mario D. Llanes-Tizoc, Alfredo Reyes-Salazar, Sonia E. Ruiz, Eden Bojorquez, Juan Bojorquez and Jesus M. Leal Graciano

    A numerical investigation regarding local (uL) and story (uS) ductility demand evaluation of steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (IGF), is conducted in this study. The interior connections are modeled, firstly as perfectly pinned (PP), and then as semi-rigid (SR). Three models used in the SAC steel project, representing steel buildings of low-, mid-, and high-rise, are considered. The story ductility reduction factor (RuS) as well as the ratio (QGL) of RuS to uL are calculated. uL and uS, and consequently structural damage, at the PMRF are significant reduced when the usually neglected effect of SR connections is considered; average reductions larger than 40% are observed implying that the behavior of the models with SR connections is superior and that the ductility detailing of the PMRF doesn\'t need to be so stringent when SR connections are considered. RuS is approximately constant through height for low-rise buildings, but for the others it tends to increase with the story number contradicting the same proportion reduction assumed in the Equivalent Static Lateral Method (ESLM). It is implicitly assumed in IBC Code that the overall ductility reduction factor for ductile moment resisting frames is about 4; the results of this study show that this value is non-conservative for low-rise buildings but conservative for mid- and high-rise buildings implying that the ESLM fails evaluating the inelastic interstory demands. If local ductility capacity is stated as the basis for design, a value of 0.4 for QGL seems to be reasonable for low- and medium-rise buildings.
Key Words
    steel building; moment resisting frames; local and story ductility; ductility and force reduction factors; pinned and semi-rigid connections; 3D models; nonlinear analysis
Mario D. Llanes-Tizoc, Alfredo Reyes-Salazar, Eden Bojorquez, Juan Bojorquez and Jesus M. Leal Graciano: Facultad de Ingenieria, Universidad Autonoma de Sinaloa, Culiacan, Sinaloa, 80040, Mexico
Sonia E. Ruiz: Instituto de Ingenieria, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Coyoacan, Ciudad de Mexico, Mexico

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