I assume you mean angles and T-Shapes/double angles when you say L & T shaped columns.
If this is the case, check out ASD Manual of Steel Construction, 9th Ed., Chapter 3. Pages 3-55 to 3-58 contain design examples for angle columns. Load charts for Double Angles and Structural Tees (WT sections) follow this.
PCA Column program does the job for you. It has very good GUI and capacity to design any arbtrary shaped column.
If you are looking for theory, the belive it would be similar to that of rectangular columns with little more involved calculations, but not very sure.
Thanks to breaks,JAE & Bannu for responding my problem,i want to clear to Breaks that my problem is related with concrete L & T shaped columns.i want to more about PCA.also
design procedure for same.
i asked about the ability of rebalcing the steel section in composit column (steel encased concrete)using the prograam PCA column
i have the version 2.2 of that program (1989) nd i want n new version of that program if it possible