Research On Flexural Performance Of Coral Concrete Beams Reinforced With Steel Fibers By GFRP Bars

With the goal of China’s ocean power and the strategy of land and sea integration,the engineering construction of remote islands and reefs is gradually carried out,and the coral in the islands and reefs is reasonably used as aggregate for concrete,which can reduce the construction cost and shorten the construction period.Due to the high humidity of the air in the marine environment and the high content of chloride ions in the coral,the steel reinforcement is very easy to rust in this environment,resulting in the safety of the structural elements.Therefore,it is very important to use coral as aggregate to avoid reducing the life of members due to steel corrosion.The corrosion resistance of FRP reinforcement,which is a lightweight and high-strength alternative to steel reinforcement,can effectively solve these problems when reinforcing coral concrete beams.However,the lower modulus of elasticity of FRP reinforcement,linear intrinsic relationship and weaker bond with concrete due to the influence of aggregates make the members more brittle and cracked.The addition of steel fibers in coral concrete,using steel fibers to enhance the toughening of concrete to improve the compressive strength of coral concrete to match the high tensile strength of FRP bars,can reduce the degree of crack development in coral concrete,improve the brittleness of coral concrete,and increase the load bearing capacity of structural members.Based on this,this paper selects GFRP tendons which are more cost-effective compared with other fiber reinforcement and steel fibers to strengthen coral concrete beams,mainly carried out as follows:(1)The mechanical properties of the materials selected for the test beams were determined by conducting tests of various strengths of coral concrete and tensile tests of GFRP bars.It was concluded that with the increase of fiber admixture from 0 to0.5% and 1.5% respectively,the concrete cubic compressive strength increased by10% and 15%,splitting tensile strength increased by 15% and 28%,axial compressive strength increased by 7% and 15% respectively,while the modulus of elasticity increased by 7% and 30% respectively.the tensile strength of GFRP reinforcement measured by the test could also meet the test requirements.(2)Design one GFRP reinforced plain concrete beam,one GFRP reinforced coral concrete beam and four GFRP reinforced coral concrete beams with steel fibers,analyze the damage pattern and crack distribution development,load displacement curve and ultimate load,concrete and tensile reinforcement strain distribution of each test beam under different reinforcement rate and different fiber dosing conditions,it can be concluded that: With the increase of reinforcement rate,the load bearing capacity grows in a positive correlation,while the cracks are produced more and more intensively and frequent due to the increase of stiffness,although the crack height and width are limited;With the increase of fiber admixture,it not only improves the compressive ability of the concrete in the top compressive zone of the beam,but also improves the tensile ability of the concrete in the bottom tensile zone of the beam,which in turn improves the ultimate bearing capacity and deflection of the test beam;Meanwhile,the addition of steel fiber causes the stress dispersion to develop towards the weaker area,which effectively inhibits the development of cracks.(3)The accuracy of the values was first verified by ABAQUS-2020 software,and the differences in ultimate load and load displacement curves between the simulated and test beams with different reinforcement ratios were further compared.The results show that the principal structure relationship of steel fiber coral concrete can be applied,while the ultimate load increase with the increase of reinforcement rate reaches 18.6% and 46.9%,respectively.(4)The ultimate bearing capacity of GFRP reinforcement-doped steel fiber coral concrete beams under flexural ultimate load was calculated.Using the national standard calculation formula found that the calculated value of each test beam and the test value of a large gap,did not consider due to the addition of steel fibers on the impact of the concrete in the tension zone,so as to amend the GFRP reinforcement doped with steel fibers coral concrete beam ultimate load bearing capacity calculation formula.By comparing the results calculated using the modified formula with the test results in good agreement,suitable for actual engineering design calculations.(5)The value of the relative bond characteristic coefficient of GFRP reinforcement and steel fiber-doped concrete is corrected as well as the corresponding change of FRP strain heterogeneity factor due to the incorporation of steel fiber,and the correction factors for the effect of GFRP tensile stress in the tensile zone due to the incorporation of steel fiber are proposed,combined with the above equation with reference to the formula for calculating the crack width of FRP reinforced concrete beams in the specification,the calculation method for the crack width of GFRP reinforcement-doped steel fiber coral concrete beams is established and its good applicability is verified.