Shear Strength of Reinforced Concrete Column Subjected to Varying Axial Load due to Vertical Motion
Project/Area Number  08650679 
Research Category 
GrantinAid for Scientific Research (C)

Section  一般 
Research Field 
Building structures/materials

Research Institution  TOKYO METROPOLITAN UNIVERSITY 
Principal Investigator 
KITAYAMA Kazuhiro Tokyo Metropolitan Univ., Dept.of Architecture, Associate Professor, 工学研究科, 助教授 (70204922)

CoInvestigator(Kenkyūbuntansha) 
KOYAMA Akio Tokyo Metropolitan Univ., Dept.of Architecture, Research Associate, 工学研究科, 助手 (90285099)

Project Fiscal Year 
1996 – 1997

Project Status 
Completed(Fiscal Year 1997)

Budget Amount *help 
¥2,500,000 (Direct Cost : ¥2,500,000)
Fiscal Year 1997 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1996 : ¥2,200,000 (Direct Cost : ¥2,200,000)

Keywords  Reinforced concrete / Column / Shear Strength / Varying Axial Load / Shear Transfer / Truss Mechanism / Arch Mechanism / 鉄筋コンクリート / 柱 / せん断強度 / 変動軸力 / せん断伝達 / トラス機構 / アーチ機構 / 加力経路 
Research Abstract 
Exterior and interior columns in reinforced concrete (R/C) frames may be subjected to axial load varying complicatedly from compression to tension in 1995 Kobe Earthquake, resulting in ill influence on shear resistant capacity of these columns, since the vertical acceleration during the earthquake was larger than that as supposed. Then four column specimens with square cross section of 250mm x 250mm were tested to study the shear strength and deformation. Shear reinforcement ratio was 0.39%. Shear span ratio was 1.0. Concrete compressive strength ranged from 275 to 298 kgf/cm^2. Column axial load and loading path between the axial and lateral load to columns were varied in the tests ; constant axial compression corresponding to concrete compressive strength ratio of 0.49, constant axial tension corresponding to concrete compressive strength ratio of 0.29, varying axial load after applying the lateral load (called separate loading) and varying axial load with the lateral load applied si
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multaneously (called simultaneous loading). Conclusions were drawn as follows. (1) Shear strength of R/C columns under varying axial load was reduced up to 0.69 times and 0.88 times that under constant axial load in tension and compression, respectively. Arakawa formula and AIJ provision for ultimate strength design of R/C buildings, which can not account for tensile column axial load, overestimated shear strength under varying axial load in tension. (2) Shear strength subjected to varying axial load in compression was almost same in two loading paths, i.e., separate loading and simultaneous loading. Shear strength in tensile axial load under the simultaneous loading, however, was 0.83 times that under the separate loading. (3) Shear force carried by truss mechanism was almost constant regardless of varying column axial load whereas contribution of arch mechanism for resisting shear changed drastically with the variation of column axial load. (4) The inclination of diagonal compression struts in concrete assumed to be formed uniformly in truss mechanism, which was computed using measured bond stresses along column longitudinal bars and measured tensile forces in shear reinforcement, was similar to the inclination of principal compressive strain under tensile column axial load. Therefore compressive stress could not be transferred across diagonal shear cracks. this is the reason why arch mechanism was difficult to develop in R/C columns under tensile axial load. (5)測定結果を用いた柱主筋付着応力度とせん断補強筋負担力とからトラス機構のコンクリート圧縮束の角度を求めて、実測した圧縮主ひずみの角度と比較したところ、引張り軸力下では両者がほぼ一致した。そのためひびわれを超えた圧縮応力度の伝達は困難と思われ、このことが引張り軸力下ではアーチ機構が形成されにくい理由である。 Less

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