Influence of the nonlinear behavior of semi-rigid connections on the analysis of low-rise steel framed structures

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2017

Öğrenci: ZAFER KARAKAŞ

Danışman: AFŞİN SARITAŞ

Özet:

In this thesis, the influence of several parameters to hysteretic behavior of semi-rigid connections on general response of low-rise special moment resisting frames (SMRF) is investigated. Two different types of low-rise structures, which are presented in SAC steel project, are taken into account. 1997 NEHRP (FEMA 1997a) and 1997 AISC provisions compliant flexible (lower bound) and rigid (upper bound) frames are selected to examine the influence of nonlinear behavior of connections on structural system response. Perimeter moment frames carry all of the seismic loads. OpenSees software is used in the analyses performed as part of this study. Beams and columns are modeled using nonlinear force-based beam-column frame elements. Semi-rigid connections are modeled using zero length rotational spring elements with hysteretic material response. In order to include P-∆ effects of gravity frames in the analysis, an additional imaginary bay with a leaning dummy column is added. Stiffness and strength due to this additional bay is negligible because leaning dummy column is pin connected at the ends and the beams are considered as rigid trusses. Nonlinear geometric effects are included by utilizing corotational transformation. Shear effect of the elements is accurately taken into consideration in the structural models. Modal, nonlinear static (pushover) and nonlinear time history analyses are conducted. The combined influences of connection rotational stiffness, yield moment and peak moment, mild or severe pinching and presence of strength loss or no strength loss are investigated in this study. Two sets of twenty ground motion records scaled to match seismic hazard levels of 10% and 2% probability of exceedance in 50 years are used for the nonlinear time history analyses. In terms of mean and median of interstory drift ratios (IDR), low-rise SMRF with semi-rigid connections do not reach collapse prevention (CP) limit of 5%. In 84th percentile of IDR, lower bound frames exceed the limit when connections are partial strength and have severe pinching with strength loss. In 95th percentile of IDR, all frames exceed the limit.