Experimental Study On Punching Shear Behaviours Of UHPC Locally Reinforced Concrete Slabs

Thin concrete slabs are prone to punching failure under concentrated loads.Traditional construction techniques such as adding column caps and punching steel bars to improve punching performance of thin concrete slabs have disadvantages such as complex construction conditions,increasing concrete dosage and compression of interlayer clearance.In order to solve the above problems,a new type of "local post-poured UHPC concrete sheet" structure is proposed in this paper.Through experimental research,numerical simulation and theoretical analysis,the punching properties of partially post-poured UHPC concrete thin slabs are studied.The main contents are as follows:(1)An innovative form of local post-poured UHPC concrete thin slab structureBased on the punching failure tests of 10 partially post-poured UHPC concrete slabs,the effects of the height,area and joint type of UHPC post-poured strip on the failure mode,crack occurrence and development,initial crack load,punching ultimate bearing capacity and energy dissipation level of concrete slabs were studied.A ductile energy dissipation index for evaluating the energy absorption of concrete sheet after punching failure is proposed for the first time.Based on the test results,the optimum size and height of UHPC postpouring belt are given.The results show that the addition of UHPC can change the failure mode of concrete thin slabs to a certain extent,promote the development of slabs from brittle punching failure to ductile bending failure,and effectively enhance the punching capacity and energy dissipation capacity of concrete thin slabs.(2)Experimental study on punching performance of partially post-poured UHPC concrete thin slabsBased on the punching failure tests of 10 partially post-poured UHPC concrete slabs,the effects of the height,area and joint type of UHPC post-poured strip on the failure mode,crack occurrence and development,initial crack load,punching ultimate bearing capacity and energy dissipation level of concrete slabs were studied.A ductile energy dissipation index for evaluating the energy absorption of concrete sheet after punching failure is proposed for the first time.Based on the test results,the optimum size and height of UHPC postpouring belt are given.The results show that the addition of UHPC can change the failure mode of concrete thin slabs to a certain extent,promote the development of slabs from brittle punching failure to ductile bending failure,and effectively enhance the punching capacity and energy dissipation capacity of concrete thin slabs.(3)Study on numerical model of refinement of partially post-poured UHPC concrete thin slabBased on the experimental results,the stress process of partially post-poured UHPC concrete thin slab is simulated and analyzed.The simulation results show that the calculated results of the finite element model are in good agreement with the experimental results.On this basis,the strength of UHPC material,reinforcement ratio,size and shape of loading plate,height and size of UHPC post-pouring belt are simulated and analyzed,and the effects of the above key parameters on punching performance of partially post-poured UHPC concrete sheet are explored.The results show that the increase of strength and reinforcement ratio of UHPC material can enhance the ultimate punching capacity of the test plate,but the effect is not significant;the increase of the size of the loading plate can significantly improve the ultimate punching capacity of the test plate,but the shape of the loading plate has little effect on the punching performance of the test plate.In addition,when the edge of UHPC post-pouring belt is 1.0-2.0 times the thickness of the plate from the loading side and the height of the post-pouring belt penetrates the thickness of the plate,the effect of improving the punching performance of concrete sheet is most remarkable,and the utilization efficiency of UHPC is the highest,which is a kind of UHPC post-pouring belt with both high performance and economic advantages.(4)A method for calculating ultimate bearing capacity of locally post-poured UHPC concrete thin slabs based on plastic hinge theory is proposed.A method for calculating the ultimate bearing capacity of locally post-poured UHPC concrete thin slabs based on plastic hinge method is proposed.The contribution of UHPC tensile strength and the influence of post-poured band size are taken into account when calculating the ultimate bending moment of single width of concrete thin slabs.A formula for calculating the ultimate bearing capacity of locally post-poured UHPC concrete thin slabs with high penetration thickness of UHPC post-poured band is established.The results show that the formulas for calculating the ultimate bearing capacity of partially post-poured UHPC concrete thin slabs proposed in this paper have clear physical meaning,reasonable calculation model and good agreement with the test results.They can be used to solve the problem of calculating the punching shear ultimate bearing capacity of concrete thin slabs with moderate thickness and area of UHPC post-poured strip.