I am trying to find through which combination of commands, I check if a particular cross section, has sufficient capacity or not, after the structural analysis. The structural analysis will determine all the inner forces within a cross section.
I think you need to find out the maximum stress on the section due to the applied external load. If external load is vertical then find out the vertical stress on the section. The stress which you have obtained from the analysis should be lesser than the structural capacity of the section. The maximum structural capacity of the concrete section is vary with respect to the grade of concrete. Further details, surely you will get from the software manual. Hope, I have answered to your question. All the best in your research work.
Surely all you get out of the opensees software is the internal stresses within the sections based on the assumptions of the Finite elements that you are using. The sectional capacities can be simply determined from basic mechanics of materials and depends on the materials that you are using. You should probably export your results to a spreadsheet and then calculate your capacities based on a code of practice (which include appropriate margins of safety) within the country or industry that you operate.
Create a Matlab script as post-processing will be helpful in this case. You can load your analysis result for each combination from opensees and write the script to check the demand/capacity ratio of your section. The capacity will be based on code of practice you are using.
Stress-based assessment may not be efficient for steel member as it experiences buckling.
MacIsaac is right except that since the element has been exposed for some time in the open seas, then you will need to determine the effective cross-section available for structural safety based on the current API code after deterioration in the aggressive environment. This intrinsic safety should conform to the current JCSS target safety for the extended service or operation period and according of the material of construction investigated using a reliable FE software.
However, if it is a new construction, then the FE with a good design software will provide the adequate sections (in steel or concrete) combined with excellent professional judgement the section tat meets bot the current API and JCSS recommendations. FERUM ma be used to evaluate the reliability or safety in both new and old constructions. Thank you.