Research On Mechanical Property Of The Reinforced Concrete Columm With HRB500MPa Steel Bars After Fire In Drawed Area

The column is the most important impression member in the reinforced concrete structure,whose mechanical property is focused widely.Especially the mechanical property of reinforced concrete column after fire is the research focus in the academic world.Firstly under the action of fire,the column is put a kind of initial damage,based on which,the normal temperature component and high temperature component is carried out static load test,then the mechanical property of reinforced concrete column after fire in drawed area is studied.Secondly based on the test,the formula of residual capacity with the reinforced concrete column after fire is inferred.The paper is studied according to test and theoretical analysis,The main work and conclusions are as the following three aspects.1.In fire experiment,the column is compressed with the axial compression ration of 0.2.The column is warmed according to the international standard heating curve,the temperature field of component is measured by the thermocouple buried in the interior of column,which laies the foundation of evaluating the high temperature damage with component.The results shows:?1?There is a offwhite line between damaged seriously concrete and danaged mildly,then the damage depth of the component would be estimated according to offwhite line;?2?There are a lot of temperature cracks focus on small cracks,mainly without through cracks,which laies the foundation of the component length in the following formula.?3?In the whole warming,the temperature of the 20mm of column and the tensile bar is as the same,so in the following calculation,the standard cube compressive strength of concrete after fire is calculated by the temperature of tensile bar instead of the temperature of concrete near the bar.2.The static load test is conduced in the normal and high temperature members severally,section strain distribution diagram,load-strain curve of the steel bar and concrete,lateral displacement of the member and N-M curve are analysed.Then the influence on the mechanical property of reinforced concrete column after fire from fire time and eccentric distance can be analysed further.The results shows:?1?The impacts on the residual capacity of column from the fire time include two sides,the first one is stiffness,fire weakens the siffness of the component,then the resistance to deformation becomes weaker.The other one is depth of compression,the fire moves the neutral axis from fire side to unexposed surface,then the depth of compression becomes small and the ultimate bearing capacity declines;?2?The influence on ultimate bearing capacity of the column after fire from eccentric distance is the similar the normal components.With the rise of eccentric distance,the ultimate bearing capacity of the column becomes small;?3?The N-M curve of the component after fire and in normal temperature has the similar variation trend,it is worth noting that the axial compression member will become compression member with small eccentricity after fire and the compression member with small eccentricity member which has the enough temperature damage will become large eccentric compressive member,the component always change into the most vulnerable direction.3.The bonding strength between bar and concrete in the drawed area after fire will reduce,which will influence the ultimate bearing capacity of the column.The isolator of bar and concrete is analysed in the paper,based on the equilibrium equation,physical equation and deformation equation,the influence on the ultimate bearing capacity of the column from the reduction of bonding strength will reflect the design tensile strength of the rebal.The design tensile strength of the stell bal after fire and the design value of compressive strength of concrete with the discount of f_cu,Tf_cu are substituted into the simplified calculating formula about residual capacity of the component inferred in this paper after the fire,then the residual capacity of the member can be got.Compared with theoretical calculation result and trial value,the error is within 25%,which proves that the formula is in point within a certain range.