Strength of Beam-column Joint in Soft First Story of RC Buildings

Title
Author(s)
Strength of Beam-column Joint in Soft First Story of RC
Buildings RC建物のピロティ接合部の強度
Halim, Sefatullah
Citation
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URL
2014-03-23
http://repo.lib.nitech.ac.jp/handle/123456789/21767
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せ᪨ ⏦ㄳ⪅ࠝ Halim Sefatullah ࠞ
ᮏㄽᩥࡣࠕStrength of Beam-column Joint in Soft First Story of RC Buildingsࠖ࡜㢟ࡋ,
௨ୗࡢ 6 ❶࠿ࡽᵓᡂࡉࢀࡿࠋ
➨1❶
Introduction
➨2❶
Literature and background
➨3❶
Specimens and experimental results
➨4❶
Strut-and-tie models
➨5❶
Design equations
➨6❶
Conclusions
The open ground story system (soft-first story) is one of the main reasons of
building damages during recent earthquakes in the world as mentioned in almost all
reconnaissance reports and studies. Researchers try to reduce the danger of the
soft-story using different methods and machineries (e.g. installing dampers, bearing
sliders and Teflon sliders above the first story).
However, it’s possible to reduce the danger of soft-first-story by using strong
and stiff columns in the first story.
In this case, the strength of the beam-column
joint above the story is mysterious. In this study, a test is conducted to investigate the strength of the joint with a larger
sectional area of the first story column compared to that of the upper stories. Two types of
buildings are considered: 1) Buildings that the first-story column is extended toward the interior
of the building; and 2) Buildings that the first-story column is extended toward the exterior of
the building. The first story is open frame and shear wall is provided in the upper stories. It is
observed that the beam reinforcements are effective to prevent the beam-column joint failure in
both types of buildings. Stirrups and hoops strengthen the joints, respectively, in the buildings
with first-story column extended toward interior and exterior. The force-resistant mechanisms
of these joints are also found to be different from those of usual beam-column joints because,
the sign of the bending moment in the second-story column is the same as that of the first-story
column. The failure modes of these joints are also different from those of the usual
beam-column joints.
Strut-and-tie models (STMs) are developed for the specimens to understand the
force-resistant mechanism of the specimens. The developed models agreed with the observed
cracks. The developed models for the joints are different from those for the usual joint: the main
difference is that, in the specimens large struts were extended into the wall panel in the second
story. STMs are also developed for the total frame to understand the overall equilibrium.
Moreover, design equations are proposed where the joint strength is evaluated as the sum of the
flexural strengths of the beam and the second-story column. In case the first-story column is
extended toward interior, the effect of the wall panel above the joint and the beam stirrups are
also considered. In case the first story column is extended toward exterior, the effect of the
hoops in the joint is also considered. It is found that the strength and failure modes predicted by
the proposed procedure are in good agreement with the test results.

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