Behavior Of The Fire Resistance Of Angle Steel Strengthened Reinforced Concrete (RC) Columns Considering Twice Loading

For the completed reinforcement concrete structure,many factors,such as the change of construction function,building aging and so on many contribute the structures are not satisfied with applicability and durability requirements.Structural reinforcement has become an important method in our life.Angle steel strengthened reinforcement is an effective method to improve the capacity of ultimate load for concrete members which section size is limited.Much research on mechanical property of angle steel strengthened reinforced concrete(RC)structure have been carried at home and abroad currently,the behavior of fire resistance of angle steel strengthened reinforced RC structure is causing growing concern.On account of under twice loading,mechanical property of angle steel strengthened reinforced concrete(RC)members is different from members without strengthened,so twice loading should be considered when the research of fire resistance of angle steel strengthened reinforced concrete(RC)columns is carried.Considering the problems above,finite element model is built under twice loading,on the basis of data of four angle steel strengthened reinforced concrete(RC)columns tested for fire resistance by our research group,the main study process and production are as follows:(1)Reference the test data of research group and reference materials to select appropriate thermodynamic property and thermal parameter of materials.(2)The model of angel steel strengthened reinforced concrete(RC)columns were built by FEA software ABAQUS.Consider burst of concrete protective coating and the heat transfer slow down by joint grouting in temperature field model.Consider the evaporation of epoxy resin adhesive between angel steel and concrete under fire,But don’t consider the contribution of mechanical of concrete cover the in thermal-mechanical couple model.(3)The results of temperature field and curve of displacement at the top of columns of numerical simulation compared with the test data of four angle steel strengthened RC columns to verify the rationality of the model.(4)Consider twice loading by deactive and reactive elements and track of elements on the basis of verify model,indicate the distribution of first force and the second force by load distribution factor n.analyse the influence of different value of n to transformation and fire resistance of angel steel strengthened reinforced concrete columns.(5)The influence of the load ratio,eccentricity ratio of the load,reinforcement ratio and size of angle steel to the fire resistance behavior of angle steel strengthened RC columns is analyzed,and compare the difference of fire resistance between strengthened with twice loading and without twice loading.On the basis of finite element analysis and design and engineering practice,summarize the adverse effect of twice loading on fire resistance of angel steel strengthened reinforced concrete columns,and give some advice on fire resistance design.