Study On Flexural Behavior Of BFRP Reinforced Seawater Sea-sand Concrete Beams With TRE Tension Zone Cover

To solve the shortage of river sand resources in coastal and island reef areas,and taking advantage of the excellent chloride corrosion resistance of Fiber Reinforced Polymer(FRP)bars,the combination of FRP bars and seawater sea-sand concrete(SWSSC)is attracting wide attention.In this paper,based on Jiangsu Provincial Key Research and Development Program “Research on key technology of FRP reinforced sea sand concrete structures with TRC/ECC formwork”,the mechanical properties of BFRP reinforced seawater sea sand concrete members and the improvement of the serviceability of beams by using Textile Reinforced ECC(TRE)to replace the concrete cover are studied.The main experimental contents and conclusions are as follows:(1)The influence of the parameters,such as the diameter,the bond length,the concrete type,the surface form of the reinforcement,the bar type and the stirrup restraint,on the bond performance between BFRP bars and SWSSC are analyzed.The results show that the slip curves of ribbed BFRP bars can be divided into micro slip stage,slip stage,descent stage and residual stage.Reducing the bar diameter and bond length,stirrup restraint and using sand-coated bars can improve the bond performance.Seawater and sea sand has no effect on the bond behavior.The analysis about bond performance based on the energy aspect is in good agreement with the experimental results.(2)The acquired bond-slip constitutive model is in good agreement with the experimental bond-slip curves.(3)The effects of the reinforcement ratio,section height,bar diameter and bar type on flexural behavior of BFRP-SWSSC beams are analyzed.The results show that the bearing capacity,crack width and deflection of FRP-SWSSC beams are much larger than those of a steel-SWSSC beam.Increasing the reinforcement ratio or the section height can increase the bending stiffness of the beam,which consequently increases the bearing capacity and reduces the strain,deflection and crack width.Beams with similar axial stiffnesses exhibit similar flexural behaviors.BFRP bars with smaller diameters are conductive to reducing the crack width,while the bearing capacity and deflection are not affected.The curvature limit of 0.005/d can meet the deflection and crack width requirements of BFRP-SWSSC beams in normal use.(4)Based on GB 50608-10 and the collected test data,the formula for calculating the maximum crack width of FRP reinforced concrete flexural members under short-term load is modified.The design method based on the bearing capacity limit state and the serviceability limit state for BFRP-SWSSC beams with double reinforced rectangular section is proposed.(5)The influences of the composite layer type,textile layers and matrix thickness on the flexural properties of TRE composite beams are analyzed.The results show that with the increase of the matrix thickness and textile layers,the failure mode of composite beams transits from tensile failure to balanced failure.The composite layer can increase the cracking load and bearing capacity of the beam to some extent.Compared with ECC and TRC composite layer,TRE can effectively delay the stiffness degradation of the beam and improve the deflection and crack width of the beam under the service load,which make it meet the requirements of the codes.The composite layer is beneficial to improve the brittleness of FRP-SWSSC beams at failure.The ductility index of beam TRE20-3 is 29.1% higher than that of the control beam.(6)Based on the section analysis method,the calculation method for predicting the flexural capacity of composite beams and the calculation formula for the optimal reinforcement ratio of textile are proposed.The experimental data are in good agreement with the calculated results.There are 90 pictures,28 tables and 150 references in this paper.