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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. |
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