Mechanical Properties And Constitutive Relationship Of LRS-FRP-constrained Concrete Short Columns

In recent years,FRP materials have been widely used in the field of concrete structure reinforcement because of their superior mechanical properties.As a new fiber material in recent years,Large-Rupture-Strain FRP(LRS-FRP for short)has superior rupture strain capacity which is far greater than 2% of traditional FRP.It can overcome the fracture problem caused by stress concentration on the corners of a rectangular column confined by traditional FRP due to its lower elastic modulus and larger rupture strain.With the same tensile stiffness,LRS-FRP confined concrete have larger deformation and higher energy absorption,so it has gradually attracted the attention of academic circles.The purpose of this paper is to provide a complete theoretical system for the seismic design of LRS-FRP-concrete-steel tubular double coupling beam systems,and to study the mechanical properties of LRS-FRP confined concrete and LRS-FRP-concrete-steel tube.The main work results are as follows:(1)The effects of the cross-section aspect ratio,corner ratio,number of FRP layers,and loading method on the failure modes,limit states,stress-strain relationships and load-unload rule of LRS-FRP confined concrete were investigated through monotonic and cyclic compression tests on 8 cylinders,24 square columns,and 24 rectangular columns.The research results show that the above parameters have a significant effect on the compression behavior of LRS-FRP confined concrete.Choosing an appropriate aspect ratio and corner ratio can greatly increase the ductility of the confined concrete while keeping sufficient compressive capacity.(2)The effects of the cross-section aspect ratio,hollow ratio,number of FRP layers,and loading method on the failure modes,limit states,stress-strain relationships and load-unload rule of LRS-FRP-concrete-steel tube were investigated through monotonic and cyclic compression tests on 40 LRS-FRP-concrete-steel tubes.The research results show that the LRS-FRP-concrete-steel tube can fully develop the performance of each material and the interaction between the materials improves the mechanical properties of the composite column.The maximum axial strain of the composite column is up to 19.4%.(3)By analyzing the experimental results of LRS-FRP confined concrete and comparing the existing strength and strain models,the ultimate strength and strain models applicable to LRS-FRP confined concrete are determined,and the parameters were redefined based on the Zhou and Wu’s stress-strain model.For the first time,a single-segment stress-strain model suitable for LRS-FRP confined concrete was established.The prediction results are in good agreement with the test results.(4)The load-unload rule of LRS-FRP confined concrete was analyzed in detail,and the stress-strain model of LRS-FRP confined concrete under monotonic loading is combined to establish the stress-strain model of LRS-FRP constrained concrete under cyclic loading.The results show that the model predicts that the hysteresis loop is in good agreement with the test results.