| Nowadays,reinforced concrete structures are widely used in various building structures,but in some special environments,the corrosion problem of reinforcement is becoming more and more prominent,which poses a challenge to the durability of the structure.As a kind of fiber-reinforced composite material,FRP rebar not only has good durability,but also has low density and high strength.It is an ideal substitute for reinforcement.At the same time,UHPC has ultra-high strength and good ductility.The combined structure of the two can give full play to their excellent properties and has a good application prospect.However,FRP rebar will have obvious performance degradation at high temperature.Compared with ordinary concrete,UHPC has high thermal conductivity and low specific heat capacity,which makes the temperature rise speed of its section temperature field faster.Therefore,the high temperature resistance performance of FRP rebar reinforced UHPC structure is poor,so it is necessary to carry out relevant research.In this paper,the high temperature resistance and bending resistance of GFRP rebar reinforced UHPC beams under fire and high temperature are studied through the finite element software ABAQUS.The specific research contents and results are as follows:(1)The research results of scholars at home and abroad on the basic theory of thermal mechanical coupling analysis,thermal properties and high temperature mechanical properties of GFRP rebar and UHPC are analyzed and summarized.It is found that the tensile properties and elastic modulus of GFRP rebar decrease rapidly at high temperature,the thermal conductivity of UHPC is high and the specific heat capacity is low,which makes its section temperature rise faster than that of ordinary concrete.After analysis,reasonable thermal parameters are selected,the thermal mechanical coupling finite element model is established,and the accuracy of the model is verified.(2)The thermal mechanical coupling analysis of GFRP reinforced UHPC beam is carried out through the finite element software ABAQUS.It is found that the residual bearing capacity of the beam decreases fastest within 30 minutes of fire,and the contribution proportion of GFRP rebar to the flexural performance of the beam becomes smaller and smaller with the increase of fire time,indicating the performance disadvantage of GFRP rebar at high temperature;For the tensile GFRP rebar at the bottom of the beam,every 5mm increase in the thickness of the protective layer can reduce the temperature of the rebar by about 50 ℃ and increase the fire resistance time by 3min to 6min;Because of the axial binding force,the fixed beam at both ends has better fire resistance than the simply supported beam at high temperature.(3)The midspan cross section temperature field of GFRP rebar reinforced UHPC beam under fire is analyzed,and the section temperature isotherms under different fire time are obtained.Referring to the calculation method of flexural bearing capacity of GFRP rebar reinforced UHPC beam at room temperature,based on the equivalent section method of threestep model,the calculation method of residual bearing capacity of GFRP rebar reinforced UHPC beam under high temperature is proposed,and The numerical simulation results are compared with the theoretical calculation results,and the results are in good agreement,which can provide reference for engineering application. |
