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Common
column design variables are probably limited to the following:
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Column
section dimensions.
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concrete
compressive strength.
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yield
strength of reinforcement.
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number
and size of rebar reinforcement inside the column section.
Structural
engineering professionals always consider practical and economical aspects
in the design of concrete column in a structure, such as:
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Symmetrical
reinforcement layout in the column cross section. Unsymmetrical layout
is not practical in column design due to reversal loading conditions,
unless the designer is dealing with clear situation, such as a column
loaded with mono-rail cantilever.
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Fixed
concrete compressive strength, at least for the columns.
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Use
of one size of rebars with a single column section. Although the use
of different rebar sizes is not prohibited by code, practical
construction would not be in favor for such design.
The
effect of these elements, or variables, is behind the effort to compile
the ready-to-use column strength interaction diagrams. Practitioner
engineers, as well as architects would appreciate this design aids to
quickly and promptly analyze concrete column using the wide selection of
ready-to-use column strength interaction diagrams.
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Range
of elements used in the ready-to-use column diagrams:
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Dimensions:
range from 10x10 inches to 18x18 inches, including some intermediate
rectangular shape columns.
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Concrete
compressive strength: Range of values used are 3, 4, and 5 ksi
concrete at 28 days. (ksi= kips per square inch).
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Steel
yield strength: One value used, fy=60 ksi.
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Number
of rebars: in selecting the number of rebars to fit into a column
section under consideration the following parameters were considered:
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Minimum
ratio of reinforcement is 1% of the column section gross area, in
accordance with ACI 10.9.1.
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Maximum
ratio of reinforcement is 8% of the gross area according to
ACI 10.9.1. However, the diagrams used around 4% ratio for
practical reasons, in order to avoid rebar placement difficulty,
and honey comb defect while pouring concrete in member congested
with reinforcement.
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