Study On Fire Resistance Of Scale Model Of Concrete Structure Based On Similarity Theory

The fire resistance test of full-scale concrete members can directly reflect the thermal response of members.However,due to the limitation of fire test equipment,full-scale members can only select some conventional sizes,and cannot carry out fire resistance test on full-scale members of super high-rise and long-span structures.The establishment of scale model for fire resistance test based on similarity theory has great advantages such as controllable parameters and short test cycle.Therefore,studying the similarity relationship between the thermal response of the scaled model and the full-scale model,and achieving the thermal response of the full-scale model through the fire resistance test of the scaled model can greatly reduce the cost of structural fire resistance test and promote the fire resistance test research of the overall structure.In order to comprehensively study the thermal response similarity between the concrete scale model and the full scale model under different sizes,this paper adjusts the structural similarity,time similarity and temperature field similarity of the concrete scale model based on the finite element software,and further studies the thermal response similarity of concrete members.The main research contents are as follows :(1)Based on the similarity theory of structural model test and heat transfer theory,it is expounded that the premise of similarity relationship of thermal response of concrete structure under different proportions is the similarity of temperature field.According to the similarity theory of temperature field and thermal response,the calculation method of actual heating curve of scale model is introduced.(2)The full-scale models of 12 groups of reinforced concrete columns were designed,and the corresponding 2/3,1/2 and 1/3 scale models were established based on the similarity theory.The actual heating curves and displacement loading rates under three proportions were established respectively.The numerical simulation of 12 groups of series columns under high temperature was carried out by ABAQUS finite element software.The finite element results show that the temperature field similarity of each series of columns is high,and the fire duration and cross-section size have little effect on the temperature field similarity.The decrease in the number of fire planes will lead to the decrease in the temperature field similarity,thereby reducing the similarity of high-temperature mechanical properties.The axial deformation similarity of each series column is higher,the larger the load ratio,the higher the structural deformation similarity.The fire resistance limit similarity of each series column is higher,the larger the scale ratio,the higher the fire resistance limit similarity.The displacement curves of high temperature bearing capacity and the fire resistance ultimate bearing capacity of each series of columns are highly similar.The larger the scale ratio is,the higher the similarity of fire resistance bearing capacity is.(3)The full-scale models of 12 groups of SRC columns were designed,and 2/3,1/2 and 1/3 scale models were established according to the similarity theory.The numerical simulation of 12 groups of series columns at high temperature was carried out by ABAQUS.The results show that the temperature field similarity of each series of columns in the section steel and surrounding concrete is high,while the temperature field similarity in the outside concrete is low,and the less the number of fire exposed surfaces,the lower the similarity.The similarity of axial deformation and fire resistance limit of each series of columns is higher than that of the reinforced concrete series columns,and the similarity decreases with the decrease of the number of fire surfaces and the eccentric action.The displacement curves of high temperature bearing capacity of each series of columns basically coincide,and the similarity is higher than that of reinforced concrete series columns,and the similarity of scale ratio has little effect on fire resistance ultimate bearing capacity.(4)The full-scale models of 9 groups of bidirectional reinforced concrete slabs and 6 groups of unidirectional reinforced concrete slabs were designed,and the corresponding 2/3,1/2 and 1/3 scale models were established according to the similarity theory.The boundary conditions of 15 groups of series slabs were transformed by ABAQUS finite element software and the numerical simulation was carried out at high temperature.The finite element results show that the temperature field similarity of each series of plates is low,and there is a large temperature gradient difference along the heat transfer direction,and the temperature field similarity near the non-fire surface is reduced.The central vertical displacement similarity of each group of plates is low,and the larger the ratio of long and short sides,plate thickness,reinforcement ratio and protective layer thickness are,the higher the similarity of some scaled models is.The boundary conditions have little effect on the hightemperature mechanical properties of each series of plates.(5)Applies the new type of steel structure waved steel bar to reinforced concrete beams.Based on the normal temperature constitutive of waved steel bar and the high temperature constitutive of linear steel bar,the stress-strain relationship of waved steel bar at high temperature is deduced.The full-scale models of nine groups of RC beams were designed by equivalent substitution method,and the 2/3,1/2 and 1/3 scale models were established based on similarity theory.The numerical simulation of nine groups of series beams at high temperature was carried out by ABAQUS finite element software.The finite element results show that the temperature field similarity of each series of beams is high,close to the non-fire side,and the similarity is reduced.The high temperature structural deformation and fire resistance limit similarity of each series of beams are high,the larger the load ratio,the higher the similarity,and the scale ratio has little effect on the fire resistance limit similarity.The high temperature bearing capacity of each series of beams is not similar.