Practical fire design of partially encased composite steel-concrete columns according to Eurocode 4

A practical method based on Campus-Massonet criteria which is developed initially to steel structures with combined compression and bending is adapted for the calculation of the buckling resistance of eccentrically loaded columns. The latter at room temperature or in fire situation is expressed by a simple formula as a function of an equivalent buckling coefficient taking into account the amount the eccentricity of the compressive applied load. The method proposed combines accuracy, efficiency and convenience obviating the need of M-N interaction diagrams and long iteration process. Otherwise, the estimation of the fire resistance for a given loading is made on the assumption based on the linearity with the level applied compressive load. It was found that the fire resistance of a column subjected to an eccentric load decreases gradually with the increase in the load level (eta), the slenderness ratio (lambda) or the amount of the eccentricity. For a fire resistance of one hour, time enough to evacuate the building of all its occupants, it recommended to use eta <= 0.5 and lambda <= 45. The range of values of reinforcement cover (u) suggested by Eurocode 4 leads to a better fire resistance except for u = 60 mm where there is a decline of the about 10%.