| When the underground reinforced concrete slab-column structure is subjected to fire,the punching shear failure will occur easily and the continuous collapse will be caused then.Experts and scholars in the field of structure pay more and more attention to the fire resistance research of slab-column structure nowadays.However,most of the existing studies only focus on the scale specimens,which cannot reflect the actual phenomenon of structure under fire.Therefore,based on the full-scale structural test,the fire behavior of underground reinforced concrete slab-column structure is studied,and the acoustic emission technology combined with infrared monitoring technology is used for analysis,and the contents are as follows:(1)In this paper,the fire test of three full-scale underground reinforced concrete slab-column structures was completed.In the process of the test,the four-point concentrated load was applied on the plate surface,and the plate bottom and slab-column joints in the furnace were directly affected by fire,at the same time,the columns and its foundation were protected against fire.The test recorded the displacement of the concrete slab and collected the temperature data of furnace temperature,different positions of concrete sections and reinforcement.Infrared ray was used to monitor the whole process of crack development on the surface of the S3 under fire.3D scanner was used to scan.Finally,under the fire condition,the temperature distribution law of the concrete slab section,the displacement distribution law of the outside and inside plane,the crack development law of the specimen under the infrared ray monitoring,the cracking phenomenon of the plate bottom and the elevation of the plate surface after the test were obtained.(2)The test results show that the test piece surface forms a series of radial radial negative plastic hinge lines in the area adjacent to the column.The radial plastic hinge line is concentrated at the support center point of the column,and the test piece has an inverted sector.The temperature field of the concrete slab along the direction of section thickness presents a nonlinear distribution,and the concrete temperature gradient close to the fire surface within 33 mm increases rapidly in the first 30 minutes.There is a significant influence on temperature rise of steel and concrete because ofmoisture,and it presented a horizontal segment of temperature rise at 100℃ in concrete.There are measuring points of displacement which the deflection is downward except for the measuring points of mid-span which the deflection is upward,and the maximum downward displacement is located in the four corners of the plate surface.There is a significant impact on the crack of concrete for moisture content.In the process of the test,there are different degrees of crack among the three specimens,and the maximum crack depth is 60 mm.(3)The acoustic emission technology was used to monitor the whole test process of the specimen.The changes of acoustic emission event rates,cumulative event numbers,energy rates and b-value of the plate under the condition of step loading under ambient temperature and heating under constant load were investigated,and the relationship between parameters and crack development and furnace temperature was analyzed.The results show that the relationship between the event rates and cumulative event numbers and the time reflects the activity change of the plate in the test process,and the high energy rates represent the release of high-intensity acoustic emission signal at this moment.The b-value of acoustic emission reflects the stress state of the specimen at a certain moment and the crack expansion in the slab at that moment.When the crack develops in a small step,the b-value is large;when the crack develops in a large step,the b-value is small,meanwhile,this moment corresponds to the large-scale failure of the specimen.Each parameter can be used to distinguish the pre-cracking stage,the concentrated appearance stage and the slow propagation stage. |
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