Study On Punching Shear Resistance Of Concrete Slabs Reinforced With CFRP Grids

Carbon fiber reinforced polymer(CFRP)grids have excellent corrosion resistance.As an ideal substitute for traditional steel bars,CFRP grids can be placed in the concrete slabs to improve the durability of the structure.In addition,CFRP grids have the characteristics of electromagnetic wave transmission,non-conductivity,thermal isolation and relatively small thermal expansion,which can be applied to engineering structures with special performance requirements.In recent years,a lot of structural collapse accidents have occurred due to the punching failure of basement roof,resulting in significant casualties and economic losses.The punching shear resistance of concrete slabs can be improved by using the punching-shear CFRP grids.At present,there are few studies on punching shear resistance of concrete slabs reinforced with CFRP grids at home and abroad,and the mature method for calculating punching shear capacity hasn’t been formed.In this paper,a combination of theoretical research and experimental research is carried out to systematically study the punching resistance of concrete slabs reinforced with CFRP grids.The research object of this paper includes two types of concrete slabs:(1)slabs where CFRP grids are used as flexural reinforcement,referred to as "concrete slabs reinforced with CFRP grids";(2)slabs where CFRP grids are used as punching-shear reinforcement,referred to as "concrete slabs reinforced with punching-shear CFRP grids".Based on the shear-compression failure theory of reinforced concrete,this paper proposes an analysis model and calculation formula of punching capacity of reinforced concrete slabs based on the height of shear-compression zone.Compared with the codes of various countries,the calculation value of punching shear capacity of reinforced concrete slabs based on the height of shear-compression zone is in good agreement with the experimental value,and the discreteness is smaller.The effect of flexural CFRP grids and flexural steel bars in concrete slabs is similar.According to the difference of material properties,the punching shear capacity of concrete slabs reinforced with CFRP grids can be calculated by the equivalent reinforcement ratio(the reinforcement ratio of CFRP grids to which it is equivalent to traditional steel bars).Based on the study of the punching resistance of normal reinforced concrete slabs and concrete slabs reinforced with CFRP grids,this paper proposes a method for calculating the punching capacity of concrete reinforced with punching-shear CFRP grids.Based on the theoretical study of the punching shear resistance of concrete slabs,the experimental research was carried out.Experimental research on punching shear resistance of six concrete slabs was carried out(One of them has double-layer two-way steel reinforcement on the top and bottom of the slab,one has double-layer CFRP grids reinforcement on the top and bottom of the slab,two have double-layer two-way steel reinforcement and punching-shear CFRP grids reinforcement,two have double-layer CFRP grids reinforcement and punching-shear CFRP grids reinforcement).The crack appearance and development,load-deflection curves,CFRP grids strain,concrete strain and failure modes were recorded and analyzed.Experimental research shows that the mechanism of punching failure of reinforced concrete slabs is basically same as that of concrete slabs reinforced with CFRP grids.Concrete slabs reinforced with punching-shear CFRP grids can effectively improve the cracking load,punching shear resistance capacity and deformation capacity of concrete slabs.The calculation value of punching shear capacity of concrete slabs based on the height of shear-compression zone agrees well with the experimental value.