Critical Buckling Time of Compressed Steel Bars Considering High Temperature Creep

Steel structures are sensitive to the risks associated with elevated temperatures, especially in the range of fire temperatures. This applies in particular to slender compressed elements such as columns, truss rods etc. These hazards are not only related to the deterioration of the mechanical properties of steel at elevated temperatures, increased deformations and stresses, but they may also cause short-term high temperature creep, which can lead to rapid loss of stability of compressed elements in a short time, with stresses significantly lower than Euler's critical stresses. Thus, for safety reasons it is important to know the time for which the structure will retain its load capacity. This paper presents the results of calculation of the critical time, after which the total loss of stability of the axially compressed prismatic steel bar occurs. Calculations were made with the use of the initial imperfection method, taking into account experimentally determined relationship between creep strain and time, in the form of epsilon(c) = f (sigma,t) = k sigma(n)t. The results of theoretical calculations were compared with the creep times obtained in the experimental creep tests of axially compressed steel members at elevated temperatures. Laboratory short-term creep tests were performed in the Instron/Satec KN 600 universal testing machine equipped with a furnace for high-temperature testing type SF-16 2230, that enables testing at temperatures up to 1200 degrees C. This paper presents only a part of the research and analyses conducted for ordinary structural steel, at 700 degrees C.