Study On Determination Method Of Steel Strength After Fire

Since the advent of steel has been widely used in the construction field,especially the steel structure buildings have sprung up in the major cities.Steel structure building fire accident occurred frequently in recent years,inspection and repair work is particularly important,steel strength after fire is the performance index which must be detected.The traditional method of intercepting sample belongs to a kind of damage method,is not conducive to subsequent repair work.This paper proposed to use nondestructive detection method-Leeb hardness method to measure the strength of steel after the fire,and established the relationship curve between strength of steel after the fire and Leeb hardness and the calculation formula.First,this paper has chosen the H-beam steel which is commonly used in steel structure as test object,experiencing high temperature process under seventy percent design pressure.Set up six different temperatures in the fire test,respectively 100 ? ~ 600 ?,made restriction on the heating time of constant temperature,the two cooling ways was used to simulate fire extinguishing,water cooling mode and natural cooling mode respectively.High temperature of specimen after cooling,according to bear the 70% stress of the residual bearing capacity after fire and Unstressed state with mechanical jack fixed two situations,the Leeb hardness values of which were measured.On the same specimens,the Leeb hardness values of 3 testing parts of the position of flange and 3 testing parts of the position of web were measured respectively.Intercept standard samples in each specimen of flange and web,measure its mechanical properties with a tensile testing machine,and record the data.Finally,The influence of factors on the hardness value are analyzed,such as cooling mode,temperature,stress state,test position and other factors,and the experimental data are analyzed by using both linear and nonlinear methods.Considering all the factors,fitted the curves of the Leeb hardness and tensile strength of the flange position and the web position,determined two regression equations,provided the basis for the detection of steel strength after the fire.