| As a reliable and efficient structural form,steel-concrete composite structure has been mature in China for more than half a century.In recent years,with the continuous enhancement of China's comprehensive national strength and the proposal of the strategy of the ocean power,the construction industry has made great progress.A large number of new materials,new technologies and new methods have been widely used in the field of architecture.As a typical representative of the stainless steel material,with its good mechanical properties,excellent corrosion resistance and beautiful appearance,it is becoming more and more popular with today's architects and structural engineers.This makes the appearance and popularization of the composite structure of stainless steel become available.However,in recent years,the frequent occurrence of building fires poses a serious threat to the safety of building structures.At present,the study of the composite structure fire resistance has become the main direction of the fire resistance research in the construction structure,but there is no relevant fire resistance design provisions for the stainless steel composite components in the current codes at home and abroad.This will bring great risks to the application of the stainless steel composite components.Therefore,the research on fire resistance of stainless steel composite beams has strong technical foresight and important theoretical value.Based on the above background,this paper studies the fire resistance of the stainless steel composite beam with rectangular cross section,reveals its behavior response and failure law in the fire,puts forward some suggestions on the fire resistance design method.The mechanical properties of materials at normal temperature and high temperature are the cornerstones of the research on the fire resistance of the components.Firstly,a series of mechanical properties tests are carried out on the stainless steel,concrete and steel materials in the rectangular section of stainless steel composite beams,and the relevant mechanical properties are obtained in a more comprehensive and accurate way.Based on the domestic austenitic S30408 stainless steel,the mechanical properties of stainless steel materials under different conditions were tested by tensile test at normal temperature and high temperature steady state test,and the mechanical properties of stainless steel at high temperature were investigated.The test results show that the two stage Ramberg-Osgood material model(R-O model)proposed by Rasmussesn and others can accurately simulate the stress-strain relationship of stainless steel at normal temperature,and the two stage R-O model of Chen at high temperature can simulate the stress-strain relationship of stainless steel at high temperature,but two The hardening exponent n and n_?and the parameters m and m_?in the model need to be corrected according to the test data.The stud connector is an essential part of composite beam.When the number of studs is fixed,the shear capacity of the studs determines the mechanical behavior of the composite beams.In view of the structural safety and the prevention of chemical corrosion between different materials(such as steel and stainless steel),stainless steel composite beams should be made of stainless steel.Therefore,in this paper,4 diameter 13mm stainless steel cylindrical studs were introduced at normal temperature,and the load slip curves of each specimen were obtained.The shear strength of 13mm stainless steel cylindrical stud at normal temperature was determined.Furthermore,the numerical simulation analysis of the shear bearing capacity of the stainless steel cylindrical stud is carried out by using the ABAQUS software,and the accuracy of the model is verified by comparing the numerical simulation results with the experimental results.On this basis,the numerical simulation analysis of the stainless steel cylindrical stud with different diameters is carried out,and the shear strength of the stud with different diameter of the stainless steel cylindrical stud is obtained,which provides an important reference for the accurate establishment of the analysis model of the anti fire performance of the stainless steel composite beam.In order to investigate the fire resistance of a stainless steel composite beam with rectangular section,by using ABAQUS software and based on the successive thermodynamic coupling analysis method,the numerical simulation method suitable for the analysis of the fire resistance of the composite beams of stainless steel composite beams is determined by the comparison of the numerical simulation methods of a variety of composite beams,and the existing composite beam fire test is used.Results verify the correctness and accuracy of the numerical simulation method.On this basis,based on the ISO834 standard temperature rise curve and the related research results of the shear bearing capacity of the stainless steel cylindrical stud,an analysis model of the fire resistance performance of the stainless steel composite beam with rectangular section is established,and the factors affecting the fire resistance of the stainless steel composite beam under the complete shear connection are analyzed.The influence of load form,load ratio n,concrete plate thickness h_c,concrete slab width b_c,stainless steel beam height h_s,stainless steel beam width b_s,concrete slab reinforcement ratio and composite beam span L on the fire resistance of the stainless steel composite beams are emphatically investigated.The results of parametric analysis show that:(1)The load ratio n,the thickness of the concrete slab h_c,the height of the stainless steel beam h_s and the composite beam span L are the important factors affecting the fire resistance of the stainless steel composite beams with rectangular section,and the most significant influence of the load is that of the n.(2)The thermal expansion coefficient of stainless steel material is larger than that of steel composite beams with ordinary structure.The stainless steel composite beam under fire will produce temperature additional bending moment due to the expansion of stainless steel beam,which has a great influence on the fire resistance of the stainless steel composite beam.(3)The greater the load ratio n,the lower the critical temperature and the shorter the fire resistance time of the stainless steel composite beams under the fire.When the load ratio is n<0.4,the influence of the vertical deformation of the stainless steel composite beam under the fire can be described as two stages:Stage I,in the pre heating period(the heating time is 0~15min),combination The vertical deformation development of the cross section of the beam is very rapid;stage II,in the middle and later period of heating up(15~40min),the vertical deformation development of the composite beam is relatively slow,and the smaller the load ratio n,the more obvious the above phenomenon is.The vertical deformation of the stainless steel composite beam is mainly dependent on the load ratio when the load ratio is more than 0.4.(4)There is a coupling relationship between the load ratio of n and the thickness of concrete slab h_c,the height of stainless steel beam h_s and the composite beam span L on the fire resistance of the rectangular cross section stainless steel composite beams.When the load is less than n<0.6,with the increase of the thickness h_c of the concrete slab,the increase of the height h_s of the stainless steel beam and the decrease of the specimen span L,the rectangular section under the fire is not rusted.The critical temperature of the steel composite beam is increased and the time of fire resistance is prolonged.When the load ratio n is more than 0.6,the critical temperature and the fire resistance time of the stainless steel composite beams tend to be consistent under the same load ratio.The fire resistance mainly depends on the size of the load ratio n,and the correlation is not strong with other factors.Therefore,in the analysis of the fire resistance of a stainless steel composite beam with rectangular cross section,it is suggested that the influence of the interaction between the factors should be taken into consideration in addition to the consideration of the influence of various factors.Finally,combined with the sectional characteristics of rectangular section stainless steel composite beams,a simplified formula for calculating the temperature field of rectangular section stainless steel composite beams is presented.On this basis,by considering the influence of temperature additional bending moment,the temperature additional bending moment coefficient K is introduced,and the maximum bending moment M of the stainless steel composite beam is adjusted and magnified,and the calculation method of the critical temperature of the stainless steel composite beam is perfected,so that the calculation method is more suitable for the prediction of critical temperature of stainless steel composite beam. |
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