箍筋约束混凝土轴心受压性能尺寸效应研究

采用高宽比为3∶1的棱柱体试件，进行了不同截面尺寸箍筋约束混凝土试件的轴心受压试验。试件分为4组，每组3个相同试件，各组试件截面边长分别为108 mm、200mm、250 mm、370 mm。为保证各组试件具有相同的混凝土约束效率，采用相同的箍筋形式，箍筋直径和间距等参数也与截面尺寸保持相同比例，以研究试件截面尺寸对箍筋约束混凝土试件的轴心抗压强度、峰值应变、延性的影响。结果表明：各组试件的裂缝开展和破坏形态基本一致，荷载-轴向应变曲线的下降段随试件截面尺寸的增大而变陡；各组试件约束混凝土的轴心抗压强度基本相同，尺寸效应不明显；峰值应变随试件截面尺寸的增大而明显降低，截面尺寸为370 mm试件的峰值应变为108 mm试件的49%，表现出明显的尺寸效应。

Size effect on behavior of concrete confined by stirrups under axial compression

Concrete specimens with different sizes confined by stirrups were tested under axial compression. Prisms with aspect ratio of 3∶1 were used in the test. The specimens were divided into four groups and each group contained three identical specimens. The sectional dimensions of specimens of the four groups were 108 mm, 200 mm, 250 mm and 370 mm, respectively. To ensure identical confinement coefficient for specimens with different sizes, the same type of confining stirrups were adopted in all specimens and both diameters and spacing of confining stirrups were properly scaled. The influence of specimen size on axial compressive strength and its corresponding peak strain and ductility of confined concrete were investigated. Similar cracking patterns and failure modes were found in the test regardless of sizes of the specimens and steeper descending branches in load-axial strain curves were observed in specimens with larger sizes. It is found that there is not apparent size effect phenomenon with respect to axial compressive strength of confined concrete, while peak strains of confined concrete corresponding to the peak stresses decrease significantly with the increase of specimen sizes. The average peak strain of specimens of 370 mm is 49% of that of specimens of 108 mm showing a significant size effect.