Uniaxial Interaction Charts For Fully Encased Composite Columns

Nowadays, steel-concrete composite construction is used to meet performance andrnfunctional requirements of mid to high-rise structures as well as large span structures.rnThese structures acquire the structural and constructional advantages of both thernconcrete and steel. Among composite members is a composite column. A steelconcreterncomposite column is a compression member, comprising either a concreternencased steel section or a concrete filled tubular steel section.rnThe resistance of a composite column to combined compression and bending isrndetermined using an interaction curve of its cross-section. Developing interactionrncurves requires rigorous section analysis. For this reason, different practice codesrnincorporated simplified analysis and design procedures. Among which, the Eurcode 4rnprovides a simplified method for composite sections and columns satisfying certainrnrequirements. According to this method, the axial force-moment interaction curve ofrna composite cross-section is obtained by assuming full plastic stress distribution.rnFurthermore, the Eurocde 4 approximates the entire interaction curve by a polygonrnmade up of four or five points on the interaction curve. Despite these simplificationsrnand approximations, the analysis of a composite section is yet computationallyrndemanding. In addition to this, for composite sections that violate the codernrequirements a more rigorous analysis is mandatory. This has been a majorrndisincentive for using composite frames. Despite their advantages, the topic ofrncomposite columns is given few attentions in the Ethiopian construction industry.rnMoreover, neither design aids nor analysis tool haven’t been developed yet to assistrnstructural engineers in analysis and design of composite columns.rnIn this thesis, more accurate uniaxial interaction curves are developed for “I” and “H”rnsteel sections that are fully encased in concrete. The stress resultants were evaluatedrnstarting with strain distributions in the ultimate limit states that were adopted from thernEurocode 2. The stress-strain laws of materials were taken from Eurocode 2 andrnEurocode 3. The stress resultants of the concrete and structural steel involved doublernintegrals of the stress over the compressed regions of the concrete and structural steelrnsection as well as over the tensioned regions of the steel section. These integrals werernivrnthen transformed into line integrals by using Green’s theorem. Finally, the linernintegrals were solved using Gauss Quadrature which is numerically exact methodrnwith the adopted material laws. Double counting of the concrete area in compressionrnzone which is replaced by the structural steel section and the reinforcement wasrnavoided.rnThe uniaxial curves developed were verified against the outputs of the software calledrnMASQUE. The comparisons indicate that the developed interaction curve is almostrnidentical with that of MASQUE output.rnTo increase the applicability of this study, especially in the Ethiopian market, arncomputer program UICISEC with a friendly graphical user interface is incorporated.rnFinally, a design example for a column length subjected to biaxial bending wasrncarried out according to the Eurocode 4 simplified method. Here, the uniaxialrninteraction curves of this study were utilized.rnKey Words: composite column, fully encased composite section, strain distributionrnin the ULS, section analysis, stress resultants, column length

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