| Reinforced concrete slabs-columns structure were initially developed at the beginning of the last century.This kind of structure building become very common for office buildings and residential as well as for parking garages for the simple structure form,convenient for construction,reduced building story heights and good economic efficiency.But in fact the slab-column connections was very complex in puching,and this subject therefore still attracts attention by researchers.At the same time,there still no Convinced puching Mechanism theory.Based on parabolic Mohr-Coulomb failure criterion,the partial differential equation that can be applied to obtain the minimum upper-bound solution of the punching shear strength of concrete column-slab connections is derived.Based on the equation,the analytical solution corresponding to the bearing capacity of circular column-slab connections and the series solution corresponding to the bearing capacity of square column-slab connections are abtained.The relevant parameter values of plastic theory are determined by summarizing the experimental punching shear characteristics of slab-column connections,and the formulas which can be effectively used in practice are derived.For circular column-slabs connections and square-column-slabs connections,the spatial distribution of stress in punching damage yield surface are analyzed comparatively,the results show that the stress at the edge of column is higher than that in the bottom of slab in both of two connections.For square column-slabs connections,stress concentration is found at the corner of the column.The plate under the action of axial force and moment punching problem is transformed into a node eccentric force effect,Based on the plastic limit analysis method,the translational-rotational compound motion mechanism model is proposed to analyze the ultimate bearing capacity of slab-column connections,and the functional is deduced.The proximate bearing capacity under partial load was calcuated with the assumed yield surface,furthermore,the results were appropriately simplified,also calculation method proposed in this paper and other calculation methods introduced in our existing specification are compared and evaluated;the comparison of the calculation method shows that the composite motion mechanism model can reflect the influence of the ratio of column to plate thickness on the bearing capacity more accurately than the eccentric shear stress model.the adjusted method proposed in this paper is accurate to the test results well.Based on plastic theory,this paper introduced a new concept,that the oblique section came into yield situation and at the same time the slab-column oblique section cracked and sliped,which caused that the punching failure in the slab-column joint.The oblique section cracking load could be derived by supposing the stress distribution on the oblique section and the plastic limit load could also be obtained on the basis of the parabola Mohr-Coulomb principle.Based on this failure mechanism,the solving methods aimed at the punching shear capacity of the slab-column joints under concentrated loads and uniformly distributed loads were obtained respectively,in addition,related parameters were corrected according to experimentalal results.The calculations were found in good agreement with the experimental datas.At last,the formulas applied to engineering practice were simplified according to the calculations.This model presented in this paper could also reasonably explain the phenomenon in which shearing-awl angle under concentrated force was greater than that under the uniform load. |
PDF Full Text Request