| Reinforcement concrete slab-column structure is a general structural configuration. It's widely used in garages and residential buildings and generally used in Europe and America, because of the advantages, such as simple formworks and small self-height which can reduce the hight and cost of buildings and so on. There may be circle and rectangle columns connecting to slab in practical structures to satisfy the building function and structure arrangement demand of users, on the other hand, slabs can be supported by short-leg shear walls in slab-column shear wall structures. Nowadays, the experimental study of the circle or rectangle slab-column connections is insufficient at home and abroad, and there are no explicit understandings about the longitudinal reinforcement ratio effect on the punching shear capacity of slab-column connections. The codes provisions from different countries of the punching shear capacity is based on semi empirical and semi theoretical other than the mechanism model of failure. It's necessary to further investigate the effects of column shape and longitudinal reinforcement ratio.In order to investigate the influence of the column section shape and longitudinal reinforcement ratio on the punching shear behavior, In this paper, on the basis of summarizing previous researches, 10 reinforced concrete slabs subjected to concentrated loading were tested. Specimen dimension is 2550mm×2550mm×180mm. the main variables of the experiment are column shape and the longitudinal reinforcement ratio:(including circle, hexagon, square and rectangle), Take longitudinal reinforcement ratio 1.28%, 0.86%, single bidirectional configuration.The load-deflection curves, the failure mode, the distribution of concrete, steel strains and the inner shear crack forming process were obtained through the tests. Analysis were combined with the test results and the existing experimental data, the results showed that: longitudinal reinforcement ratio affects deformation properties obviously, improves slab-column connections punching capacity partly, specimen punching failure occurs when the maximum bending moment portion of the longitudinal reinforcement yield; there is no significant effect on the punching capacity when the column length-width ratio is between 1and 4; the basic reason of the negative effect of the column section shape on the punching shear capacity was the stress concentration due to the increase of the ratio um/h0 and the assumed angle of the punching shear surface and the consideration for the calculation of the slab-column with circle column were unreasonable; on the other hand, the inner shear crack was firstly formed at the upper area nearing the column, then develop up and down leading to punching shear, which is not perfectly plastic.Comprehensive comparison four kinds of codes widely used in the world can be considered, the codes EN 1992-1-1: 2004 and MC 2010 can better reflect the influence of longitudinal reinforcement and column section to the punching shear capacity. In this paper, based on twin shear strength criterion and the theory of rigid-plastic punching failure punching shear capacity of slab-column node was deduced by the theoretical formula calculation, a good agreement with the formula to calculate the test results, the theoretical formula and the collected historical data contrast, also good agreement. |
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