Abstract
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 (ƞ) , the slenderness ratio (λ) 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 η≤ 0.5 and λ ≤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%.
Highlights
The theoretical evaluation of the fire resistance of partially encased composite steel-concrete columns is very complex, and is not practical for everyday design
The Eurocode 4 unfactored eccentric load strength was based on the cross-section and column axial load bending moment strength interaction diagrams, which needs in the first step to be calculated
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
Summary
The theoretical evaluation of the fire resistance of partially encased composite steel-concrete columns is very complex, and is not practical for everyday design. Often of a quick and easy application, its results are generally very conservative as it predicts very high values for the required reinforcement This method is still useful, at least in the preliminary design stages, where it can be used to choose between a composite steel-concrete structure and an equivalent steel structure with adequate fire protection. The material properties for each zone are modified using reduction factors, which depend on the average temperature in the zone These temperatures are determined by considering the section to be exposed to an ISO fire for the required fire resistance period. The aim of the present investigation is to present an efficient simple and practical method for the calculation of the buckling load resistance of an encased composite steel-concrete columns subjected to eccentric loading
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