how to find maximum axial , shear and bending moment carrying capacity of a section used in a STAAD model based on various lengths of members used in a particular model.

Hi

I have to design connection for sections in steel structure.

And as per our client and applicable codes requirement I have to ensure that while designing connections , apart from maximum end forces coming on members, the connection should also be designed for some minimum percentage of its max. load carrying capacity (i,e axial ,shear and bending). say for example max. axial froce Fx coming on a bracing is 100 KN , but max. axial load (compression) carrying capacity of that bracing for that particular member length is 500 KN and code says connection should be designed for min. 50% of its max. capacity. than i have to design it for 250 KN.

I can find out the max. force coming on a member , but how i can find out the maximum capacity of that type of section in a particular STAAD model , because max. load carrying capacity such as compression and bending varies based on its length for a single section type in a particular model.

So please suggest -

how to find maximum axial , shear and bending moment carrying capacity of a particular section type used in a STAAD model , based on various lengths of members used in a particular model. as axial (compression) and bending moment carrying capacity will vary in a single model based on its length.

Thanks in advance.

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  • An approximate way to get the maximum load carrying capacity is to do a steel design and look at the interaction ratio. For any member, the reciprocal of that value tells you how much additional capacity that member possesses. For example, if the highest ratio for a member is 0.85, the reciprocal is 1.176, which means, the member can take about 17.6% more load.

    Note that the interaction ratio is not linearly related to the applied load, so, this can only give you an approximate estimate.

    Another way is to do a buckling analysis and look at the buckling factors. First, the factor would have to be greater than 1. The amount in excess of 1.0 is the additional load carrying capacity for the structure, since this analysis is based on the weakest member in the structure. The tedious aspect of this method is, you have to do the buckling analysis for every combination case, find the lowest positive buckling factor from among all the cases, and find the reserve capacity on the basis of that.