In this study an algorism for the computation of Interaction Surface of reinforced concrete Tshapedrncolumn subjected to axial load and biaxial bending is developed. The method is exact andrnit is based on the transformation of the double equilibrium integrals into line-integrals along therncompressive perimeter of the concrete section using Greenâ€™s Theorem. For up to third degreernpolynomial stress-strain relations, Gauss integration with only three sample integration pointsrnyields exact results.rnBy inserting the necessary cross-sectional dimensions and material properties on the userrninterface, the program locates the position of the plastic centroid of the cross section. Therncoordinates of corner points and reinforcement bars will be calculated using the cross sectionalrndimensions and position of the plastic centroid.rnThe interaction charts produced are for reinforcement ratios of 0 to 0.8 with an increment ofrn0.1.Parabolic-rectangular stress distribution is used for the analysis of the concrete section as isrnprimarily recommended by EBCS-2,1995. The capacity of the section is checked for differentrnpositions of neutral axis. Greenâ€™s theorem transforms the double integration over therncompression area into a line-integration along the closed line that encloses the area. The linernintegration along the perimeter of the compression area of the section is numerically evaluatedrnusing Gauss integration.rnThe calculation of the stress and force carried by the steel is straightforward. From the strain werncalculate the corresponding stress and finally the force on each bar. Note that from the stress ofrneach compressive bar we subtract the stress of the concrete at the location of that bar in order tornavoid double counting the compressive concrete area displaced by the bar.rnThe presented method for the construction of Interaction Surfaces of concrete sections isrncomputationally efficient because the double integration is reduced to numerical evaluation of arnfew line integrals. The number of line integrations is equal to the number of the sides of thernsection in the compressive zone. Each of these integrals involves typically three sample pointsrnthus the number of computer operations is very small.rnAlthough the initial objective of the study was to develop interaction chart for T columns; in thernprocess of solving the problem other possibilities are also achieved. The program developed canrnalso produce interaction surface of L and rectangular columns. Six of these interaction surfacesrnare shown in appendix A. It is clear that the computation time would allow the interactive use ofrnthe method as a design tool. The program is written in visual basic programming language.