Experiment And Process Simulation Of High Performance Concrete At High Temperatures Under The Coupling Of Vapor Pressure And Thermal Stress And Load Action

High performance concrete(HPC)is extensive used in constructional engineering for its good working performance,high volume stability and and excellent durability.The spalling of HPC at high temperatures lead to an influence on bearing capacity of constructure and normal working function,because spalling of HPC will weaken the section of supporting member.The influence facter of HPC spalling at high temperatures are vapor pressure,thermal stress,load and the coupling of these factors,it is necessary to study the internal stress,strain,deformation,energy variation process,and uncover spalling mechanisum and how PP fiber restain spalling mechanisum of HPC at high temperatures under the coupling of vapor pressure,thermal stress and load.This thesis is supported by National Science Foundation of China(51478290).High performance concrete slab mixed without polypropylene fiber(Named NHPC)or high performance concrete slab mixed with polypropylene fiber(Named PPHPC)with a strength grade of C80 was prepared,and these slab was used in the coupling of vapor pressure,thermal stress and load experiment.The coupling of thermal stress and load numerical simulation of high performance concrete and the coupling of vapor pressure,thermal stress and load numerical simulation of high performance concrete with experiment parameters.The result of experiment and simulation were hoped to be the reference for stress and strain and displacement and energy variation process and spalling mechanism of high performance concrete at high temperatures.Main content of this thesis as follows:1.The coupling of vapor pressure and thermal stress and load Experiment of high performance concrete at high temperaturesThe prepared NHPC slab and PPHPC slab was used in the coupling of vapor pressure,thermal stress and load action experiment under fire condition.The experiment result shows that: NHPC slab was spalling after fire heating 27 min,the spalling area is over 80% area of the whole fire heating surface at the end of experiment.The side of NHPC slab generated much macro crack.But PPHPC slab didn`t spalling over the whole heating time,only a few micro crack and macro crack happens in the heating surface.The temperature test results show that the temperature of the fire has a great influence on the temperature of the NHPC and PPHPC at 25 mm,and has a small influence on the 50 mm.The results of thermal strain test show that the strain difference between NHPC slab and PPHPC slab at 50 mm in the same loading time is relatively small.The strain of the NHPC continued to increase after the fire time of 25 mm was over 30 min,while the strain of PPHPC gradually decreased,and then the small amplitude increased,and then decreased significantly.1.The coupling simulation for thermal stress and load of high performanceconcrete at high temperaturesThe experiment parameter of NHPC slab and PPHPC slab fire heating experiment was used in the coupling of thermal stress and load simulation.Analyzing the variation of the temperatures,equivalent stress,equivalent strain,thermal strain,the gravity direction deformation and strain energy of NHPC slab and PPHPC slab in the simulation.The result of simulation shows: Variation trend of temperatures nephogram internal force nephogram displacement nephogram and energy nephogram of NHPC slab and PPHPC slab is in accord with experiment.Temperature has a big impact on temperatures von-mises stress,vonmises strain,thermal strain,gravity directional deformation and strain energy of the position which within 25 mm distance from heated surface of NHPC slab and PPHPC slab,on the contrary,50 mm distance from heated surface of NHPC slab and PPHPC slab,these parameter shows little effect by the temperature but much effect by the internal force.The position which are 50 mm and 75 mm distance from heated surface of NHPC slab and PPHPC slab shows big influence by the variation of deformation and internal force which caused by high temperatures.2.Microscope simulation for the coupling of vapor pressure and thermal stress of high performance concrete at high temperaturesThe scanning patterns of NHPC and PPHPC specimens obtained at room temperature by CT technology were binarized,vectorized,smoothed and imported into ANSYS workbench finite element analysis software.The cross sections of NHPC and PPHPC specimens were subjected to steam pressure at elevated temperatures.And stress,strain,displacement and energy changes under load.The cross-section is taken as the plane parallel to the surface of the fire,at the same position from the fire surface(ie,stratosphere),the temperature curve under test conditions and the modified vapor pressure test value are applied under the thermal stress-steam pressure coupling effect.simulation.The simulation results show that the results of equivalent stress under the effect of vapor pressureload coupling are consistent with the experimental results,and the thermal strain simulation results are greater than the ultimate strains of NHPC and PPHPC.The existence of steam pressure does not increase the internal strain of high strength and high performance concrete.Instead,the internal strain of high strength and high performance concrete is relieved because of the presence of holes and tunnels.The thermal strain exceeding the ultimate strain of concrete is the main reason for the spalling of high strength and high performance concrete.one.The strain energy of NHPC in the 25 mm stratosphere is much higher than that of the high strength and high performance concrete.The strain energy of the NHPC at 50 mm and PPHPC in the 25 mm and 50 mm stratosphere are all smaller than the fracture energy,and the different materials in the thermal strain test.The actual results at different locations are consistent.