Experimental Study And Analysis On Fire Resistance Of Prestressed RPC Beams

With the continuous development and innovation of the construction industry and the emergence of high-performance materials,Reactive Powder Concrete(RPC)has developed rapidly since it entered China at the end of the 20 th century.RPC is a new type of concrete material with super-high strength and super-high performance,which is widely used in large-span structures,super-high-rise buildings,salt lakes,marine environment,underground buildings and other fields.Because of its compact structure and low permeability,RPC is more likely to burst at high temperature than ordinary concrete.Stress relaxation and creep of prestressing tendons at high temperature,mechanical properties degradation of reinforcing bars and so on will make the bearing capacity of prestressing structures seriously degraded and even collapsed.There is a lack of effective research and design methods on fire resistance and failure mechanism of prestressed RPC beams,and the research results on fire resistance of prestressed RPC beams have not been reported at home and abroad.Therefore,in view of the above scientific and technological problems,the fire resistance test research and analysis of pre-stressed RPC beams are carried out.The main work is as follows:(1)This paper makes a systematic study on the fire resistance performance of prestressed RPC structure,and designs and produces 8 prestressed RPC simple supported beams with load level,prestressed reinforcement layer thickness,prestressed bar type and prestress degree as test parameters.The fire resistance test under the condition of ISO834 standard heating was carried out by using 150? high temperature dry thermal curing.The test data of temperature change,deflection-fire time curve,effective prestress,crack development,burst distribution and depth in beam are obtained.The results show that the thickness,load level and type of prestressed bar protective layer are the key factors affecting the performance of prestressed RPC beam,and with the decrease of thickness of protective layer and the increase of load level,the flexural deformation of the specimen under fire is significantly improved,the fire resistance limit is reduced,and the performance of bonded prestressed RPC beam is better than that of unbonded prestressed RPC beam.Under the design of the fitting beam at room temperature,the damage of the specimen is easy to occur under the fire.(2)The nonlinear transient temperature field model of prestressed RPC Beam is established by the theory of heat conduction,and the fine model of prestressed RPC beam performance analysis is established based on the ABAQUS finite element software platform,considering the influence of the thermal coupling effect of concrete,the high temperature creep of prestressed steel bar and the creep of high temperature.The correctness of the refinement model is verified by comparison with the experimental data.Through the analysis of the expansion parameters,the influence of the parameters such as load level,thickness of longitudinal bar and prestressed reinforcement layer,prestress degree,section size and comprehensive reinforcement rate on the fire resistance of prestressed RPC beams is studied.The results show that with the increase of initial load level and the decrease of protective layer thickness,the fire resistance limit of prestressed RPC beams decreases gradually;with the increase of section size,the fire resistance limit of prestressed RPC beams increases,while the influence of prestressing degree and composite reinforcement ratio on the fire resistance of prestressed RPC beams is relatively small.(3)This paper analyzes the influence of the performance of prestressed RPC beam of each parameter,determines the key parameters affecting the performance of prestressed RPC beam and the influence law of key parameters,and puts forward the recommended value of section size of prestressed RPC beam,the recommended value of concrete protective layer thickness,the recommended value of comprehensive reinforcement rate,etc.Some scientific and reliable suggestions are put forward for the fire safety of prestressed RPC beams.