Keywords: confined concrete, concrete column, stress-strain, stirrup, solid, frame.

Most of the studies that are made for increasing the strength of concrete under longitudinal and lateral loads, show that this can be possible by he use of concrete additives and lateral reinforcement. Confinement increases both the compressive strength and the ductility of concrete. The energy absorption capacity of concrete also increases by increasing ductility. As the percentage of lateral reinforcement increases, the energy absorption capacity of concrete increases.

In this study rectangular column sections are chosen for virtual experiments. Concrete is modeled as solid and stirrups are modeled as frame elements which carry axial loads only. Calculations are made for different stirrup step spacings.

Column supports are chosen as fixed support. The limit loading condition is calculated according to concrete class and the column is loaded in this calculated limit condition. For determining lateral stress, stirrup axial forces are calculated and divided by the column cross section area. At the column start and end, stress distribution is not uniform. So cross sections for analysis are taken from the middle part of column. The stress-stirrup step spacing relationship is determined and curves are drawn.

Experiments are made for many stirrup step spacing values from 2.5 cm to 50 cm. Also in this study, lateral stresses of confined rectangular columns are determined as a function of stirrup step spacing. The calculated lateral stresses are used for determining a proper stress-strain relation model for confined columns. This model is compared to other confined concrete models and comparisons show that this model is effective for confined concrete columns.

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