Ultimate axial load and moment interaction diagrams for prestressed HPC thin-walled short columns

In order to lighten the prestressed concrete solid members, nowadays, it is possible to make use of the advantage of HPC (fc>60 MPa) as well as replacing the solid section with a PSC thin-walled section for certain members such as circular and box columns. Using the strength theory of ACI, a numerical procedure along with a computer program was developed for the analysis of such sections subjected to axial compression or tension load and bending moments. The program solves for all possible variables such as, concrete compressive strength (fc= 60-100 MPa), type of prestressed steel, concrete cover, ratio of wall thickness to the section dimensions and the PS steel arrangements to satisfy the given loading cases, thus leading to an optimal cost solution. However, since the cross section is thin-walled circular or box and the PS steel is located at discrete points along the periphery of a circle or rectangle, the equations of equilibrium are complex for hand computations (especially for circular section) but suitable for computer program. So, by use of MATLAB software the interaction diagrams were also drawn for the analysis of such sections for all mentioned variables. The use of such diagrams is a safe and easy tool for the analysis of such columns. Finally the results are compared with the worked examples and a very good agreement is achieved.