| Reinforced concrete slab-column structure that can effectively reduce the building height,has the advantages of quick and simple construction,convenient pipeline layout,good comprehensive benefits,flexible plane layout,large use space,etc.As a common form of architectural structure,RC slab-column structure can better meet the requirements of architectural space and use function.However,the joint area of slab-column structure is subject to complex forces,and punching failure is likely to occur.Once punching failure occurs to individual joints of the structure,the original load borne by them will be redistributed to adjacent nodes,which is easy to cause continuous collapse of the structure.At present,scholars at home and abroad have conducted a lot of exploration and research on the slab-column joints of reinforced concrete slab-column structures,but most of the existing research results are experimental studies on the mid-column joints,and few on the side-column joints.In addition,a small number of tests on the edge-column joints are usually focused on their seismic performance,and there are even fewer tests on the anti-punching performance of the edgecolumn joints.Due to the existence of unbalanced load under the action of gravity,the stress state of the edge-column joints becomes more complex.Therefore,this paper studies the failure mode and stress performance of the edge-column joints.Taking the ratio of longitudinal reinforcement as the control variable,the punching test was carried out on two edge-column joints with hidden beam,and the load displacement curve,the distribution characteristics of concrete strain,longitudinal reinforcement strain and stirrup strain were obtained.The failure modes of slab-column joints were discriminated by using the formula of the failure modes of slab-colum joints.In addition,the results obtained from the formulas for calculating the punching strength of slab-column joints in China,the United States,Europe and the United Kingdom are compared and analyzed with the test values.Finally,the loading process of the two specimens was simulated and analyzed with ABAQUS software.The longitudinal reinforcement ratio and the longitudinal reinforcement arrangement mode were taken as variables respectively,and the edge-column joints with hidden beam were parameterized and analyzed with ABAQUS software.Through the above research,this paper has drawn the following main conclusions:a)In the failure stage,the tensile longitudinal bars of the two specimens have yielded.The stirrups of E-SC-1 did not yield,and the concrete was crushed along the periphery of the column in the compression zone with a large range of crushing zone,resulting in bending failure.Part of the stirrup of E-SC-2 with a high reinforcement ratio yielded,and the concrete in the compression zone around the column was not obviously crushed,resulting in punching failure.Both specimens showed good deformation ability during the failure process,but the specimens with higher reinforcement ratio had relatively small deformation ability.b)The ratio of longitudinal reinforcement has obvious influence on the mechanical behavior of the edge-column joints with hidden beam.The initial yield load,bending stiffness and ultimate load of the specimens all increase with the increase of the longitudinal reinforcement ratio.The distribution of tensile longitudinal reinforcement stress along the column strip and the hidden beam is not uniform.In the state of ultimate load,the longitudinal reinforcement within the range of 3-4 times effective plate thickness from the column edge basically enter the yield state,while the specimens with higher reinforcement ratio have a relatively small yield range.c)Since the partial unbalanced bending moment of the edge-column joint in the short side will transfer to the floor in the form of linear shear stress,the stirrup strain in the short side is gradually larger than that in the long side.In the failure stage,the stirrup strain within the range of 1-2 times effective plate thickness from the column edge rises sharply.So it is advisable to strengthen the anti-punching measures within the range of 2 times effective plate thickness from the column edge.However,the provision of Chinese code on the allocation of anti-punching reinforcement within the range of 3 times effective plate thickness from the column edge is reasonable and safe.d)When the load is around 75%Vu,the radial strain of concrete along the short side first appears the phenomenon of "unloading" in the range of about 1 times plate thickness away from the column edge,while the radial strain of concrete in other ranges only shows strain unloading when it is close to the failure.e)In the limit state of normal use,radial and circumferential cracks have appeared around the column range of the edge-column joints.However,the deflection,concrete compressive strain,longitudinal strain and stirrup strain are all at a relatively low elastic level.f)Among several formulas for determining the failure modes of slab-column joints,Wang Baoan's formula accurately predicted the failure modes of the two specimens in this experiment.According to the unbalance moment measured in the test,for the edge-column joints in this test,the shear force transferred by the unbalance moment accounts for about 30% of the design value of equivalent punching load.Among the formulas for calculating the punching and cutting capacity of the codes of various countries,the results of GB50010-2010 and ACI318-14 are similar,and the shear capacity is in good agreement with the design value of the equivalent impact shear load,while the results of the European code EC2-04 are the most conservative.g)Parameterization analysis results of edge-column joints with ABAQUS software show that increasing the ratio of longitudinal reinforcement can improve the punching shear capacity to a certain extent.When the ratio of longitudinal reinforcement is less than 1%,the improvement is greater.In the case of a certain total reinforcement ratio,by increasing the proportion of longitudinal reinforcement of hidden beam,the punching shear capacity of boundary column joints can also be improved to a certain extent.When the ratio of longitudinal reinforcement is less than 1%,the improvement is greater. |
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