Journal of Structural and Construction Engineering (Transactions of AIJ)
Online ISSN : 1881-8153
Print ISSN : 1340-4202
ISSN-L : 1340-4202
ELASTIC-PLASTIC BEHAVIOR OF STEEL AND CONCRETE COMPOSITE COLUMNS WITH CRUCIFORM STEEL
Yo KURATOMITeruhisa TANAKAJunichi SAKAI
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2021 Volume 86 Issue 780 Pages 331-341

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Abstract

 The authors have designed and developed steel-concrete (SC) columns without reinforcement bars. The SC columns are composed of only cruciform steel and concrete, and they had an octagonal cross-section. In a previous work, an experiment was conducted on SC columns (section dimension: 190 mm × 190 mm) under cyclic and horizontal loads to investigate their earthquake-resistant performance. The experiment could not consider the scale effect of the concrete, which makes it difficult to evaluate the compressive strength of the concrete. In this study, four large-scale SC specimens were tested to investigate the scale effect of the concrete. The large-scale SC specimens were of dimensions 500 mm × 500 mm, and the shear span ratio of the SC columns was three. The experimental variables considered include the size of the cruciform steel, compressive strength of the concrete, and axial-load ratio. The small-scale specimens were tested with both ends fixed, whereas, the cantilever type was adopted for the large-scale specimens. The loading device was designed to subject the columns to an axial load N and horizontal load Q. The tests were conducted using a universal testing machine. For all the tests, the specimens were subjected to a constant axial load while the horizontal load was applied. The displacement amplitudes were increased uniformly and repeated two times at each amplitude peak.

 All specimens under an axial-load ratio n = 0.3 exhibited a very ductile behavior until the end of the test. Contrarily, under a high axial-load ratio of above 0.5, an abrupt degradation in the flexural strength was observed at a rotation angle R = 2.0%. The experimental maximum strength of the large-scale specimens exceeded the plastic-collapse mechanism line obtained by assuming a plastic hinge being formed at the fixed end of the column. The superposed strength was calculated from the yield strength of the steel and the compressive strength of the concrete. For the small- and large-scale specimens, no significant difference was observed in the axial strain and failure mode. The comparisons of the experimental results of the small- and large-scale specimens suggest that the scale effect of the concrete has little effect on the structural performance of SC.

 The flexural strength calculated based on the superposed strength or linear distribution of strain was assumed to be the estimated short-term allowable flexural strength of the SC columns. The flexural strength calculated based on the superposed strength was in good agreement with the flexural strength at the yield point of the steel flange in the tests. The rotation angle R at short-term allowable flexural strength was approximately 0.5%.

 An analysis on the elastic–plastic behavior of the SC columns was also conducted using the method that takes into account the concrete confined by the cruciform steel. The effect of the concrete confined by the cruciform steel was obtained from the axial compressive-test results of the small-scale specimens. Although the analytical results were somewhat underestimated compared with the experimental results, they pursued well with the experimental results up to a large deformation.

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© 2021 Architectural Institute of Japan
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