Numerical Investigation Of High Strength Concrete Steel Encased Composite Short Columns

Abstract

A concrete-steel composite is structural materials composed of two different materials joined together and acting as a unit. High strength concrete encased steel composite columns are those that can carry heavy loads with a smaller cross section and are used worldwide in the construction of high-rise buildings and other massive structures. It has many advantages, but the topic of composite columns has received little attention in the construction industry, especially in Ethiopia. Ethiopian Standard Euro Norm 4 provides methods to design composite columns, but it has some restrictions for concrete class, restricted to maximum C50/60. By using high strength concrete grades as per Ethiopian Standard Euro Norm 2, the researcher investigated this restriction that assists structural engineers in the design and analysis of composite columns. The objectives of this paper are to discuss the numerical investigation of the performance of high strength concrete steel encased composite short columns subjected to axial loading and the development of uniaxial interaction diagrams using finite element analysis. The finite element package ABAQUS 6.14 is used to analyze the capacity of composite short columns. In the finite element analysis (FEA), C3D8R was used for solid elements (concrete and structural steel sections) and T3D2 was used for reinforcements. Seventeen (17) column specimens were assembled in to four (4) groups by considering high strength concrete, configurations of longitudinal bars and structural steel section shapes. The EBCS-EN 2015, Eurocode-4 and British standard codes are used in this paper. Concrete damage plasticity (CDP) was used for modeling the material properties of concrete and plastic for structural steel, reinforcement bars and steel plate. The structural performance was investigated, including load carrying capacity, load displacement response, axial stiffness, ductility, failure modes and a uniaxial interaction diagram. For the validation of the model, simulation was conducted for an axially loaded composite short column test specimen from published literature. The load carrying capacity of the composite columns increased by 5.08% and compressive damage decreased by 36.1% as the high-strength concrete increased from fck = 60 MPa to fck = 90 MPa. Decreasing spacing between longitudinal reinforcement bars having the same area of reinforcement but different diameters and numbers of bars improved the capacity of composite short columns. Having the same area of section of structural steel but different structural steel section shapes changed the column`s capacity; it has been observed that from I-section shape to channel section shape, column capacity decreased by 10.72% maximum. And the uniaxial interaction diagram for high strength concrete and minor eccentricities with structural steel I-section was analytically derived using a simplified method that was reasonably close to the numerically observed N-M diagram. Finally, an analytical study was developed for column capacity, which shows a good correlation with experimental tests and finite element analysis (ABAQUS 6.14) results.