Size effect of concrete members applied with flexural compressive stresses |
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Authors: | Jang-Ho Jay Kim Seong-Tae Yi Jin-Keun Kim |
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Affiliation: | (1) Department of Civil & Environmental Engineering, Sejong University, 98, Kunja-dong, Kwangjin-gu, Seoul-si, 143-747, South Korea;(2) Present address: Department of Civil Engineering, Chung Cheong University, 330, Wolgok-ri, Kangnae-myun, Cheongwon-kun, Chungbuk-do, 363-792, South Korea;(3) Department of Civil & Environmental Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusong-dong, Yusong-gu, Daejon-si, 305-701, South Korea |
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Abstract: | In this study, two types of special experiments are carried out to understand flexural compressive strength size effect of
concrete members. The first type is an ordinary cylindrical specimen (CS) with a fully penetrated and vertically standing
plate type notch at the mid-height of the specimen, which is loaded in compression at the top surface (e.g., in the parallel
direction to the notch length). The second type is a general double cantilever beam (DCB), which is compression loaded in
axial direction (e.g., in the parallel direction of the notch). For CS, an adequate notch length is taken from the experimental
results obtained from the compressive strength experiment of various initial notch lengths. The trial tests to select the
effective initial notch length show that CS with an initial notch length approximately greater than four times the maximum
aggregate size fails without an additional increased load and in stable manner under Mode I failure mechanism. Therefore,
the initial notch length to the maximum aggregate size ratio of 4.0 is used for all size specimens. For DCB, the eccentricity
of loading points with respect to the axial axis of each cantilever and the initial notch length are varied. In both specimens,
the compressive loads apply flexural compressive stresses on the crack tip region of the specimens. These two types of specimens
fail by Mode I crack opening mechanism. By testing 3 geometrically proportional size specimens for CS and DCB, the experimental
datum for flexural compression size effect of concrete are obtained. Using the obtained flexural compressive strength size
effect datum, regression analyses are performed using Levenberg-Marquardt's least square method (LSM) to suggest new parameters
for the modified size effect law (MSEL). The analysis results show that size effect is apparent for flexural compressive strength
of specimens with an initial notch. For CS, the effect of initial notch length on flexural compressive strength size effect
is apparent. For DCB, flexural compressive size effect is dependent on the eccentricity of loading points with respect to
the axial axis of the cantilever beam. In other words, if DCB specimen is applied with greater tensile stress at the crack
tip, the size effect of concrete becomes more distinct. The results show that the flexural compressive strength size effect
of initial notch length variation of DCB exists but directly dependent on the loading location. This is due to the fact that
the sizes of fracture process zone (FPZ) of all DCB specimens are similar regardless of the differences in the specimen slenderness
ratio, but the flexural compressive and tensile stress combinations resulting in stress concentration at the crack tip region
has direct effect on size effect of concrete members. |
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Keywords: | cylindrical specimen double cantilever beam eccentricity flexural compressive strength initial notch length size effect |
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