Howdy,
Apologies in advance as I am just an EIT so I might not be using the best verbiage. I work as a structural engineer for a company that designs a lot of structures for electrical substations. Risa3D is the only 3D modeling software we use as it is perfect for these small isolated structures we tend to design.
I have recently realized that there is a bit of an issue in the way that we go about designing some of these structures and everyone in my department is now kind of scratching their heads wondering what the most efficient way to proceed would be. I haven't been able to find a decent question for this online so I decided I'd finally make my first post.
I am going to use a 4 column, 3 phase, electrical switch support stand as an example here.
When designing a structure like this we basically have two frames in the long direction that have horizontal bracing connecting them together. Mounted on top of our long beams will be the equipment, in this case switches, and I have selected their bases in the blue. This equipment is being connected to our structure via rigid vertical links in order to account for the center to center eccentricity between our beam and the switch base (everyone here, myself included, hates using the I&J offset variable in the "additional properties"). Historically we have always modeled all of the equipment's elements as rigid members in the model and so that we can directly apply our linear and point loads directly onto a model that calculates the distribution for us and then puts the resultant loads at the top of our structure (I can explain further if needed). However, what has recently come up as a point of discussion is that these bases that I have highlighted are contributing to the horizontal frame action of the structure by transferring axial load and coupling out moments. This is NOT our design intent. We need to design our structures to be able to handle the loads being applied by the equipment and our scape ends at the beams, the switch bases are a product designed by the supplier of the equipment.
So we are now kind of at an impasse at this point. We cannot change the bases to have a pin-roller condition because we need the loads being applied to the switch to distribute properly between either side of the structure. I guess what I am wondering is if there is a way I can make the model calculate and distribute the switch loads to the top of the structure and then have them "deleted" or no longer included in the calculation of strength and serviceability of our structure. I understand that I could break out these models into two separate ones or add load distribution to our MathCAD sheets where we calculate the applied loads but both of these options would greatly slow down our design times for these structures. Does anyone know of a simple fix to basically label these bases as non-structural members in the eyes of Risa?
Would love to hear any thoughts or suggestions here.
Cheers,
- Dux
Apologies in advance as I am just an EIT so I might not be using the best verbiage. I work as a structural engineer for a company that designs a lot of structures for electrical substations. Risa3D is the only 3D modeling software we use as it is perfect for these small isolated structures we tend to design.
I have recently realized that there is a bit of an issue in the way that we go about designing some of these structures and everyone in my department is now kind of scratching their heads wondering what the most efficient way to proceed would be. I haven't been able to find a decent question for this online so I decided I'd finally make my first post.
I am going to use a 4 column, 3 phase, electrical switch support stand as an example here.
When designing a structure like this we basically have two frames in the long direction that have horizontal bracing connecting them together. Mounted on top of our long beams will be the equipment, in this case switches, and I have selected their bases in the blue. This equipment is being connected to our structure via rigid vertical links in order to account for the center to center eccentricity between our beam and the switch base (everyone here, myself included, hates using the I&J offset variable in the "additional properties"). Historically we have always modeled all of the equipment's elements as rigid members in the model and so that we can directly apply our linear and point loads directly onto a model that calculates the distribution for us and then puts the resultant loads at the top of our structure (I can explain further if needed). However, what has recently come up as a point of discussion is that these bases that I have highlighted are contributing to the horizontal frame action of the structure by transferring axial load and coupling out moments. This is NOT our design intent. We need to design our structures to be able to handle the loads being applied by the equipment and our scape ends at the beams, the switch bases are a product designed by the supplier of the equipment.
So we are now kind of at an impasse at this point. We cannot change the bases to have a pin-roller condition because we need the loads being applied to the switch to distribute properly between either side of the structure. I guess what I am wondering is if there is a way I can make the model calculate and distribute the switch loads to the top of the structure and then have them "deleted" or no longer included in the calculation of strength and serviceability of our structure. I understand that I could break out these models into two separate ones or add load distribution to our MathCAD sheets where we calculate the applied loads but both of these options would greatly slow down our design times for these structures. Does anyone know of a simple fix to basically label these bases as non-structural members in the eyes of Risa?
Would love to hear any thoughts or suggestions here.
Cheers,
- Dux
