| At present,the development of the South China Sea is one of the hot spots of the development of China’s marine economy.A large number of artificial structures need to be constructed.However,in some island areas far from the mainland,there is a shortage of river sand and fresh water resources for concrete pouring.And the steel bars in concrete structures are vulnerable to corrosion in marine environment.As a result,the combination of Basalt Fiber Reinforced Polymer(BFRP)with seawater and sea-sand concrete can effectively alleviate the problems above by using the characteristics of excellent acid-alkali corrosion resistance,light weight and high strength.A new type of BFRP reinforced concrete short column which adapts to the marine environment is presented in this paper.By using BFRP bars as longitudinal reinforcement,spiral continuous BFRP strips as constraint element to improve the compressive strength of concrete indirectly.And the concrete protective layer is retained outside the strip,which is of great significance to the fire resistance of columns.The tensile properties of four different layers for BFRP sheets and the compression and tensile properties of three different diameter for BFRP bars were tested in this paper.The mix proportion experiment for 8 groups of seawater and sea-sand concrete has been carried out and the optimum mix proportion of target strength was obtained.By the axial compression test of 11 seawater and sea-sand concrete short columns reinforced with BFRP spiral strips+BFRP bars,the effects of the BFRP longitudinal bars reinforcement ratio,the number of layers,width and space of BFRP strips on the bearing capacity and ductility were analyzed.On the basis of the working mechanism,the calculating formula for compressive bearing capacity of concrete short column reinforced with BFRP spiral strips+BFRP bars is deduced.Specific findings are as follows:(1)The tensile stress-strain curve of BFRP sheet is linear without yield point,and it belongs to brittle failure.The tensile strength of 2 layers,3 layers and 4 layers increases 2.66%,4.81% and 9.96% respectively compare with that of 1 layer.The relationship between tensile modulus,elongation at break and the number of layers is not obvious.(2)The tensile strength of BFRP bars is about 2～3 times of compressive strength.The compressive elastic modulus is similar to tensile elastic modulus,which is about 1～2 times of concrete elastic modulus.Both compressive and tensile stress-strain curves have no yield point,and BFRP bars belong to brittle failure.There is no obvious law on the influence of failure mode on ultimate strength,elastic modulus and elongation.(3)Compare with unconstrained short colum,the bearing capacity of constrained short columns with BFRP spiral strips is increased by13.84%～37.97%,and the ultimate deformation is increased by16.39%～130.82%.With the same constraint indexes,the bearing capacity of constrained short column with BFRP spiral strips is 78.3% of that of short column with spiral steel stirrups,and the ultimate deformation is 47.0% of the latter.With the same conditions,the higher reinforcement ratio of BFRP longitudinal bars,the greater the width and the smaller the space of the BFRP strips,the higher the axial bearing capacity of the short column.But with the increase of the number of strip layers,the bearing capacity decreases first and then increases.The deformation capacity of short columns increases to a certain extent with the increase of reinforcement ratio for BFRP longitudinal bars.Change the number of layers,width and spacing of BFRP strips has no obvious effect on the deformation capacity of short columns.(4)In the axial compressive short columns with BFRP spiral strips,the utilization rate of BFRP longitudinal bars is between 30.91%～97.46% and the average utilization rate is 53.44%.The contribution rate of BFRP longitudinal bars to the compressive bearing capacity of short columns is between4.96%～31.97%,and the average contribution rate is 17.30%.The cooperative work between BFRP strips and concrete is better than that between BFRP bars and concrete,which can provide reference for marine aggregate concrete with BFRP reinforcement.(5)Based on the calculation formula of compressive bearing capacity deduced in this paper,the ultimate bearing capacity derived from which is close to the test value.When the effect coefficient under the lateral compression of BFRP spiral strips is 2.26,the average relative error is 8.3% and the formula can predict the axial compressive bearing capacity of such members well. |
