| Compared the normal concrete filled steel tubular column(CFST),the special shaped concrete filled thin-walled steel tubular columns(SSCFST)can save 8%-26% construction cost as well as benefit for aesthetic and interoperability in the decorate stage.These advantages indicated that the prefabricated structure has great application value and market prospect.In this study,the effect of SSI on special-shaped concrete filled thin-walled steel tubular with steel ribs frame structures has been researched.The major works are as below:(1)Heating and cooling test on T shaped concrete filled thin-walled steel tubular long columns with steel ribsBased on the ISO834 standard temperature rise curve,fire resistance of 5 T shaped concrete filled thin-walled steel tubular long columns have been tested.Temperature-time curve of steel tube,steel rib and core concrete in the key point was obtained.The results showed that the steel tube and concrete core close to it have an approximately consistent trend with the average temperature of furnace.The concrete core achieved same temperature requiring more time with the increasing of distance of test point far from the steel tube,which means that the heating hysteresis is more obvious.(2)Static mechanical test on T shaped concrete filled thin-walled steel tubular long columns with steel ribs after fireIn this study,the effect of heating time,steel ribs and eccentricity on T shaped CFTST long columns with ribs after fire.The experiment including 1 specimen at ambient temperature and 5 specimens after fire.The failure mode,load-deformation curve,load-strain curve of steel tube and residual bearing load were measured and compared to the specimens with the same parameter at ambient temperature.The results showed that the T shaped CFTST long columns with ribs belonged to bending failure and correspond to multi local buckling converges on the middle of the long columns.The axial compressive load and bending capacity decreases of the specimens after the fire but still have good bearing capacity and deformability.(3)Numerical simulation and analysis of T shaped concrete filled thin-walled steel tubular long columns with steel ribs after fireThe theoretical model of T-shaped CFTST-LC with steel ribs under temperature field was established to analyze the axial and bending behavior.The key parameters including thermal parameters of materials,constitutive relations,contact model ect are determined.The comparison between numerical results and experimental results in this study and former researchers has validated the reliability of the model in this paper.(4)Parameter analysis and empirical model of residual bearing load of T shaped concrete filled thin-walled steel tubular long columns with steel ribs after fireBased on the numerical model,the influence of heating time,section diameter,material strength(including steel pipe,steel bar and concrete)and steel ratio on axial compressive bearing capacity,bending bearing capacity at ambient temperature as well as residual bearing capacity after fire were analyzed.The formulae of residual bearing capacity after fire of T-shaped CFTST-LC subjected to ISO-834 standard was proposed.(5)Seismic behavior based on SSI effect and numerical simulation of special-shaped concrete filled thin-walled steel tubular long columns with steel ribs after fireBased on SSI effect,the seismic performance analysis model of T-shaped CFTST-LC frame structure considering the soil-structure interaction was established and verified.The vibration mode and natural vibration period of the frame subjected to fire previously are obtained via modal analysis and compared with the frame without fire.Through the structural dynamic time history analysis,the variation of the maximum acceleration,the maximum story displacement angle and the maximum inter story shear loading of the frame before and after local fire under frequent and earthquake fortification was obtained.The results showed that the fire increases the natural vibration period of the frame.Compared with the calculation results based on rigid foundation assumption,acceleration amplitude of the structure and foundation considering the soil-structure interaction decrease.The maximum interlayer displacement angle is mainly determined by the acceleration of the structure and foundation,which occurs at the bottom of the structure.The softer the soil is,the greater the amplitude of seismic acceleration is,the more obvious the fire effect is,and the greater the interlayer displacement angle is. |
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