mechbadem, the saddle ltself is usually just treated as a beam subject to external loading. Longitudinal due to wind, seismic, bundle pull, etc. Vertical due to seismic, dead weigtht, etc. Find the moment of intertial of the built up section, s = MC / I.
Influence of saddle loads on the shell may be done by a Zick-type analysis.
Recommend you get a standard handbook such as Moss, Bednar, etc.
Regards,
Mike