| Fire accidents are one of the major construction accidents that threaten public safety and social development.Compared with earthquakes,typhoons,and tsunamis,their occurrences are random,susceptible,unpredictable,and high-frequency.The mechanical properties of the structure have a great impact.However,there are few studies on slab-column structures under fire,and most of the slab-column structures studied are reinforced concrete slab-column structures,so the mechanical properties of new slab-column joints and slab-column structures at high temperatures are limited by ABAQUS Meta-simulation analysis.In this paper,by comparing the relevant experiments and related literature,the relevant parameters required for ABAQUS to perform finite element simulation calculations are determined.The finite element software is used to establish the reinforced concrete slab-column joints and the combined joints of steel tube-confined concrete columns and reinforced concrete slabs.The mechanical properties of the joints under the combined action of high temperature and external load are analyzed.Methods: A new type of structure,such as diagonal steel bars and octagonal concrete-filled steel tubular columns,was proposed and compared.The specific conclusions reached are as follows:(1)When the slab-column joints have different fire-receiving surfaces,the temperature field on one side is basically similar,and the temperature of the slab-column joints will rise rapidly when the two-sided fires occur;The faster the internal diffusion,the gradient from the internal temperature to the external surface temperature appears;the cross-section size of the column has little effect on the temperature of the internal steel bar;the thickness of the protective layer has a large effect on the temperature of the steel bar.As the thickness of the layer increases,the heating rate of the internal steel bar is also continuously reduced,and the better the fire resistance of the entire joint.(2)The ultimate bearing capacity of a slab-column joint of a steel tube-confined concrete column and a reinforced concrete slab at room temperature is 906.02 KN.After two hours of fire,its bearing capacity drops to about 80% of its original bearing capacity.The bearing capacity has dropped to about 70% of the original bearing capacity.From the analysis of the overall bearing capacity decline trend,the longer the fire,the faster the rate of structural degradation.After comparing the influence of the cross-section size of the column on the structural bearing capacity,it can be seen that the ultimate bearing capacity of the slab-column joints,and the overall trend increases with the increase of the cross-section size of the column.The thickness of the steel pipe was changed,and it can be seen that changing the thickness of the constrained steel pipe has little effect on the increase of the ultimate bearing capacity of the structure,and has little effect on the joints.(3)Analysis by ABAQUS finite element software shows that when the relative reinforcement ratio of the diagonal reinforcement is 50%,the ultimate load force is increased to 2.1%;when the relative reinforcement ratio of the diagonal reinforcement is 75%,the ultimate load force is increased to 5.8%;when the relative reinforcement ratio of the diagonal reinforcement is125%,the ultimate load capacity is increased to 8.3%.It can be seen that the larger the relative reinforcement ratio,the more the structural bearing capacity is improved.(4)An octagonal steel tube constrained concrete column and a reinforced concrete slab combined node,in which the pillar has a 12.5% reduction in the cross-sectional area of the main sub-section compared to the previous pillar,and its bearing capacity is improved under different fire exposure times.When exposed to fire for 30 minutes,the ultimate bearing capacity increased by 7.45% and the displacement was 0.0024 m.When exposed to 60 minutes,the ultimate bearing capacity increased by 10.46% and the displacement was 0.003 m.When exposed to 90 min,the ultimate bearing capacity increased by 7.54 %,The displacement is 0.0036m;the ultimate bearing capacity is increased by 5.7% and the displacement is0.0044 m when exposed to fire for 120min;the ultimate bearing capacity is increased by 7.7%and the displacement is 0.0047 m at 150 min exposed to fire;at 180 min exposed to fire,The ultimate bearing capacity increased by 10.87%,and the displacement was 0.0062 m.(5)A slab-column joint structure consisting of a single-layer octagonal steel tube constrained concrete column and a reinforced concrete slab was established,and a finite element simulation was performed to analyze the stress cloud diagrams at room temperature and60 min and 120 min under fire.It shows the direction of its force transfer and the tendency of destruction. |
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