Research On Fire Resistance Performance And Reinforcement After Fire Of Pouring Floor Integrated PC Hollow-core Slab With Constraints

Prestressed concrete hollow slab(PC hollow-core slab)is widely used in our country.The research on the fire performance of simply supported PC hollow-core slab has been reported.However,majority of PC hollow-core slabs work with constraints in the construction project.To simulate the constraints applied to PC hollow-core slab under working conditions,the negative moment rotational of the floor was achieved by pouring edge beams beams around it in experiments.And the vertical displacement was restrained by placing the side beams on the horizontal furnace wall.The four PC hollow-core slabs worked together coordinately through the 50mm laminated layer casted on the top of them.To learn the fire resistance performance of floor integrated PC hollow-core slab(PCHSF)with constraints,mechanical performance after fire and reinforcement method after fire.8 PCHSF specimens were manufactured.Each specimen consisted of four PC hollow-core slabs,constraining beams and laminations.8 PCHSF with constraints were studied in static tests under ambient temperature,in fire endurance experiment,in bearing capacity tests after fire and the reinforcement experiment after fire.The comparison of finite element(FE)simulation and theoretical calculation were carried out.The main conclusions are listed as follows:(1)The bearing capacity of 1 PCHSF with constraints was tested under ambient temperature.The cracking load,ultimate load,crack development,cross strains and failure mode of the specimen were studied in the experiment.It shows that the ultimate bearing capacity of PCHSF is much larger than the total of 4 single PC hollow-core slabs owing to the contribution of side beams and laminated layer.The results provided load data for the experiments under and after fire.(2)FE simulation on the flexural behavior of PCHSF with constraints were carried out by software ABAQUS.The flexural capacity of PCHSF was calculated based on the theoretical algorithm of plastic hinge.Finite element and theoretical results were both coincident with the experiment data.(3)The fire endurance of 3 PCHSF was tested under load.The load ratio is respectively 0.3,0.5,0.7.The section temperature field,failure characteristics and fire performance in different moment under fire were comparatively studied.The results indicated that the fire endurance of PCHSF decreases by the increase of load ratio.(4)The results of FE simulation of temperature field which achieved by using software ABAQUS agreed well with the experiment results.According to this,the nonlinear coupled thermal-mechanical analysis of PCHSF was completed.Analytical results of fire time-midspan deflection curve and fire endurance agreed well with experiment results.The numerical simulation analysis of the fire resistance of PCHSF with constaints is carried out when the load ratiao varied from 0.2 to 0.9.The fire endurance formulas of PCHSF with constraints under different load ratio levels of were obtained.(5)The flexural behavior of 3 PCHSF with constraints which were exposed to fire during different time(30min,60min and 90min)under the same load level(0.3)were tested under ambient temperature after natural cooling.The cross temperature field during heating and cooling,residual bearing capacity of specimens and flexural deformation under and after fire,were studied in the experiments.It shows that residual deflection rose gradually with the increase of time under fire.The ultimate load and initial cross stiffness decrease with a parabolic law relationship by the increase of time on fire,the corresponding formulas were also obtained.(6)The cross temperature field of specimen was simulated during heating and cooling and the flexural ability of PCHSF with constraints after fire was analyzed by ABAQUS.The results indicate that the cross temperature field during heating was apparently different from heating process.The simulation of ultimate load and load-displacement curves of PCHSF with constraints after different time under fire were consistent with experiment results.(7)The mechanical performance of fire-damaged PCHSF strengthened with CFRP sheets and steel beam was studied by static load test under ambient temperature.The results indicate that the ultimate bearing capacity of specimen after reinforcement respectively increased by 20.8%and 40.3%comparision to specimen without fire and fire-damaged specimen without reinforcement.The strengthened specimen peeled of between CFRP sheets and PC hollow-core slabs.FE simulation of strengthened specimen was achieved by software ABAQUS.The simulation of ultimate load,failure mode and load-displacement curves of fire-damaged PCHSF strengthened agreed well with experiment results.