Flexural Behavior Analysis Of GFRP-concrete Box Composite Beam

The appearance of FRP-concrete composite structure can effectively solve many problems of steel-concrete composite structure and pure FRP structure.However,due to the limitation of FRP material properties(such as low stiffness and brittle failure),the optimal design of FRP-concrete composite structure should be carried out,and the response of composite structure under the action of repeated loading should be the key consideration.In this paper,a GFRP-concrete box composite beam structure is presented.Based on the characteristics of the composite beam structure,the flexural behavior of GFRP-concrete box composite beam is analyzed.In this paper,the bending process of GFRP-concrete box composite beam under external loads is analyzed theoretically and the theoretical formulas of ultimate flexural capacity under two failure modes are obtained.The hysteretic performance indexes of the inelastic dissipative energy curve,hysteresis loop,stiffness curve and skeleton curve are obtained after the simulation analysis of GFRP-concrete box composite beam under the low cyclic load by ABAQUS.In the analysis and calculation process,the constitutive relation of the selected materials in the simulation model,including the elastic-plastic parameters of concrete,the damage evolution process,the engineering constants of GFRP and the failure criterion,are discussed in the paper.The mechanical behavior before and after failure of all the composite beam materials is fully considered,so as to achieve the goal of closer simulation and practice.For concrete,the damage factor is used at the beginning of the plastic stage until the material fails.For GFRP,the corresponding user subroutine UMAT is written according to the failure criteria of the material,and the reduction of stiffness is carried out after failure.In this paper,the influences of the factors such as the laying angle of GFRP in the web,the strength of concrete flange,and the thickness of GFRP web and base plate on the hysteretic performance of composite beam are analyzed.The results show that the laying angle of GFRP in the web has a great influence on the shape of hysteretic curve,but has little influence on the ultimate bearing capacity of composite beam.Different GFRP laying methods will affect the ductility of composite beam.The concrete strength in the flange of composite beam is not the higher the better,the higher the concrete strength is,the easier it leads to brittle failure.The larger the web thickness of the composite beam is,the better,butthe cost should be considered.The thickness of base plate of composite beam should be selected to ensure that the failure of composite beam is under-reinforced.The above research results can provide useful references for the application of GFRP-concrete composite beam.