Experimental Study On Bearing Behavior Of Prestressed Reactive Powder Concrete Beams After Fire

RPC,as an ultra-high performance concrete material,has remarkable durability and application prospect in large span,high-rise and underground buildings.The combination of RPC and high strength prestressed steel bar to form prestressed RPC beam can give full play to the excellent performance of the two,so as to reduce the structure self-weight,expand the structure span and increase the durability.With the increasing of fire frequency,the structural fire resistance design of prestressed RPC Beams has been widely concerned by researchers at home and abroad.The structural refractory design needs to meet the safety performance under the structure fire and after the fire,even if there is no major damage to the prestressed concrete structure in the fire,but the fire causes the mechanical properties of concrete,prestressed steel bar and non-prestressed steel bar to degrade,which brings hidden danger to the safety performance of prestressed concrete structure after fire.The results of the study on the mechanical properties of prestressed RPC beams after fire have not been reported,and as the main load-bearing components,the prestressed RPC beams lack effective refractory design methods.Therefore,it is of great theoretical significance and practical value to study the mechanical properties of prestressed RPC beams after fire,and to put forward the calculation method and damage assessment of the residual bearing capacity of prestressed RPC beams.In view of this,the paper mainly carried out the following work:(1)RPC is prepared by using ordinary sand instead of quartz sand.For the mechanical performance test of RPC cube test piece,the 120 MPa RPC mix ratio suitable for the normal temperature curing condition of the construction site is selected.Six bonded and two unbonded prestressed RPC beam specimens were made.(2)According to the principle that the fire resistance limit is close,the test pieces PRPCB1,PRPCB2,PRPCB3,PRPCB4 are in the same furnace,and the test pieces PRPCB5,PRPCB6,UPRPCB1,and UPRPCB2 are tested in the same furnace.According to the IOS834 standard heating curve,the test furnace is subjected to the temperature deformation of the test piece,and the physical quantity such as temperature reaches the fire end limit,and the load is removed to prevent the test piece from collapsing and collapse.The test data such as the fire temperature and time,the bursting of the beam side and the beam bottom,the crack distribution and the failure mode of the prestressed RPC beam specimen after the fire were collected,and the test specimen beam was compared with the reference after the static load.(3)The prestressed active powder concrete beams with different key parameters,such as thickness of protective layer,load level,prestress degree,non-adhesion force and anti-fire test,were tested at room temperature static load.Based on the test results and numerical analysis of 8 specimens,the load-deflection curve,crack distribution and development,deformation characteristics and damage mechanism and failure mode of prestressed active powder concrete beam after fire are obtained.The influence of the parameters such as thickness of protective layer,load level,prestress degree,with/without adhesion force on the mechanical properties of the post-fire/unbonded prestressed RPC beam is put forward.Based on the temperature field under fire,a practical calculation method for the residual bearing capacity of prestressed RPC beams after fire and a method for calculating the stiffness degree and crack width of prestressed RPC after fire are put forward.