Experimental Study And Numerical Analysis On Fatigue Performance Of Prestressed Concrete Beam And Slab After Fire

With the rapid development of bridge technology in our country,there are more and more prestressed concrete beams and bridges.Overloaded vehicles and vehicles transporting inflammable and explosive goods are increasing day by day.The probability of bridge fire is greatly increased.After the bridge fire,the fatigue performance and fatigue life of prestressed concrete beams and slabs change under repeated vehicle loads.Aiming at the fatigue performance and fatigue life of prestressed concrete beams and slabs under fatigue load after fire,this paper mainly studies the following aspects:(1)Using reinforced concrete test blocks and prestressed concrete beams and slabs to carry out fire tests and finite element numerical simulation,the variation law of concrete internal temperature field under different fire conditions is studied,and the temperature field distribution in different depth ranges within the concrete is measured.The test results show that the temperature field inside the concrete is distributed step by step with the distance from the fire receiving surface.When the temperature of the measuring point reaches 100℃,a platform will appear.The duration of the platform is related to the distance from the fire receiving surface.(2)Through the fatigue test of prestressed steel strand after fire,the fatigue performance and fatigue life of prestressed steel strand after fire are studied.The test phenomenon shows that the fatigue failure of steel strand is brittle failure.The fatigue life of steel strand after fire decreases more and more with the increase of temperature and stress amplitude.However,when the stress amplitude is small and the temperature is low,the fatigue life of steel strand decreases less.Finally,the S-N curve and calculation formula of steel strand with temperature change after fire are fitted by using the test results.(3)Based on the fatigue tests of prestressed concrete beams and slabs,the forms and characteristics of fatigue failure of prestressed concrete beams after fire are studied,as well as the development rules of compressive strain of concrete at the top of beams,strain of steel bars and mid-span deflection of beams and slabs under fatigue load.It is found that the three increase with the increase of fatigue load times and gradually spread.(4)Based on the finite element software ANSYS,the test beam is numerically analyzed,and the selection of element type and material constitutive relation,as well as the loading and solution are studied.The formula for calculating the fatigue life of the beam and slab is fitted through the numerical simulation results.Finally,the formula is modified by using the test data to obtain the modified fatigue life calculation formula for the beam and slab after fire.