Hi there, I am after some advice on how to correctly model an existing portal frame building. It is a fairly long-winded explanation so please bear with me!! The portal frame consists of two bays across its width, with the interior column (that separates the two bays) joining the rafters at the apex of the building. Adjacent to the main portal columns (approximately 600mm inside) are columns that support an overhead traveling crane. These crane support columns are approximately two thirds the height of the main portal columns and are orientated 90 degrees to the main portal columns. The crane support columns are tied back to the main portal columns via horizontal I-section members spaced at approximately 1000mm centers up the length of the column. These horizontal I-section members are fully welded to the inside flange of the main portal columns and at the other end, fully welded to the web of the crane support column. In addition to the horizontal members tying the columns together, there are also diagonal members running between opposite ends of the horizontal members. These diagonal members are welded to the top flange of one horizontal member at one end and then welded to the inside flange of the main portal column just underneath the opposite end of the horizontal member above. In summary, these members tying the crane support column back to the main portal column form a ‘N’ pattern truss like structure.
The interior columns that separate the two bays are also composed of multiple members and also act as the crane support columns at the interior of the shed for each bay. They consist of two vertical I-section members approximately 1200mm apart, orientated so that the major x-axis of the members is parallel to the plane of the portal frame. These two I-section members continue to the same height as the crane support columns at the exterior of the building. Tying these two members together are horizontal I-section members spaced at approximately 1000mm centers up the length of the column. These horizontal members are welded to the web of the vertical I-section members at either end of the horizontal members. Support of the apex at the interior columns is via an I-section column that runs from the apex of the portal frame down to the very top horizontal cross member that ties the interior crane support columns together.
This is where my question arises. When modeling this structure in a structural analysis program, how do I correctly model the composite members to achieve the correct member forces?? If I just assume that all the members in the composite columns are rigidly connected to each other I get very large support reactions at the base of the columns. When I say very large support reactions I mean in comparison to if the portal frame was modeled using singular exterior and interior columns. How do I overcome this problem or is this right?? Any help/advise would be greatly appreciated as it has got me stumped. Thanking you for your time. Axle.
The interior columns that separate the two bays are also composed of multiple members and also act as the crane support columns at the interior of the shed for each bay. They consist of two vertical I-section members approximately 1200mm apart, orientated so that the major x-axis of the members is parallel to the plane of the portal frame. These two I-section members continue to the same height as the crane support columns at the exterior of the building. Tying these two members together are horizontal I-section members spaced at approximately 1000mm centers up the length of the column. These horizontal members are welded to the web of the vertical I-section members at either end of the horizontal members. Support of the apex at the interior columns is via an I-section column that runs from the apex of the portal frame down to the very top horizontal cross member that ties the interior crane support columns together.
This is where my question arises. When modeling this structure in a structural analysis program, how do I correctly model the composite members to achieve the correct member forces?? If I just assume that all the members in the composite columns are rigidly connected to each other I get very large support reactions at the base of the columns. When I say very large support reactions I mean in comparison to if the portal frame was modeled using singular exterior and interior columns. How do I overcome this problem or is this right?? Any help/advise would be greatly appreciated as it has got me stumped. Thanking you for your time. Axle.
