Checking the Flexural-Torsional Stresses in Power Plants Pipe Supports Steel Frames

摘要

The LRFD stress checking of steel members in the latest revision of STAAD.pro v.8i doesn't include the checking for Torsional Stresses. For steel members supporting pipes, which are very common in power plant projects, it is important to check the combined Flexural-Torsional stresses in order to qualify these steel members in accordance with AISC design guide #9. Thus, the engineer has to calculate the applied torsional stresses manually using the tables and charts available in this design guide and then has to combine these torsional stresses with the flexural stresses, obtained from STAAD.pro, using either hand calculations or some computer tool. In either case, the procedure will be time consuming especially if there are a large number of load combinations to be considered. In order to expedite the process of the LRFD Flexural-Torsional checking using the output results of STAAD.pro, an Excel workbook is developed and programmed to import the steel members' geometries and their "Enveloped" LRFD forces from STAAD.pro analysis and to calculate the Torsional Stresses at different places along any steel member of the structure, as well as the other member stresses, by just inputting their start and end member and joint numbers. The stress ratios for the Shear, Flexural and Torsional stresses as well as the combined interaction stresses are then automatically computed and displayed within few minutes. It is shown that performing the LRFD steel design by STAAD.pro without accounting for torsion, in such structures, can produce misleading results.