open access

https://doi.org/10.14943/doctoral.k16126

https://hdl.handle.net/2115/93641

Dynamic Analysis of Steel Moment-Resisting Frames Considering Panel Zone Yielding, Local Stiffening due to Bracing Connections, Beam Local Buckling and Fracture

英語

2024-09-25

Hokkaido University

iv, 260, 6p.

Numerical simulation based on beam-column elements cooperated with fiber sections has been widely applied in structural analysis and design due to its high efficiency in computation. However, simulated results based on such models are generally affected by modeling schemes, such as selections of element and material models, connections between elements, simplifications of structural components, etc., and thus reasonable results always rely on appropriate models. In Japan, moment-resisting frames (MRFs) are generally constructed by square hollow-structural-section (HSS) columns and I-section beams. Seismic behaviour of panel zones in such columns is typically complicated by many factors, such as interaction of axial force and biaxial bending moments, stiffening from brace connections, and presence of composite slab, etc., and thus modeling of panel zone with consideration of these factors is one of the challenges in simulation. Furthermore, steel MRFs subjected to extremely large or repeated earthquake excitations may suffer from local buckling and low-cycle fatigue at beam ends. Significant losses of structural stiffness and strength usually accompany local buckling and low-cycle fatigue, which may result to excessive deformation of structure or even collapse. Therefore, this study focuses on modeling schemes for steel MRFs taking account of panel-zone yielding, stiffening from brace connections, and beam local buckling and fracture, and examination on how closely recorded responses of shake-table tests could be reproduced. Panel zone responses for modeling study were measured from shake-table tests on a nearly full-scale, 10-story steel moment-resisting frame with buckling-restrained braces (BRBs). The specimen was subjected to the 3D JMA Kobe motion, scaled from 25% to 100%. During the 100% JMA Kobe motion, the 10-story specimen yielded in the 1st to 8th stories developing maximum story drift ratio of 0.020 rad at the 2nd story. As expected, the column and panel zones in the interior grid point yielded under biaxial forces, while the connecting beams remained elastic. Methods to estimate panel-zone shear force were devised based on equilibriums of free-body diagrams. A panel zone model with a strut representing the stiffening from brace connection was calibrated to match the measured column inflection points and panel-zone deformation. Time history analysis of the frame using the calibrated model reproduced the experimental results with acceptable consistency. Local buckling of beams was simulated by a piecewise linear material model, which considered strength degradation at compression side. Low-cycle fatigue of beams was simulated by a material with fatigue limits based on a linear cumulative damage rule. Two material models were introduced to a force-based beam-column element, and then calibrated by cyclic loading tests on beam-and-column subassemblages. A numerical model with the proposed modeling scheme of beams was built in OpenSees to simulate a 1:2.5-scale, 4-story steel MRF subjected to unidirectional excitation of JMA Kobe-NS record scaled from 10 to 100%. The 4-story model reproduced the measured responses before fracture with acceptable consistency. Simulated beam of the exterior joint at 2nd floor fractured at the same excitation and same zone among the section with the experiment. Finally, limitations and possible solutions for future work of the proposed beam model are provided.

2024-09-25

甲第16126号

博士(工学)

(主査) 教授 岡崎 太一郎, 教授 菊地 優, 准教授 高井 伸雄

工学院（建築都市空間デザイン専攻）

博士論文

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