I have joined multi curve to one polycurve by Dynamo. But I can’t select and use it to create a swept blend element.
Anyone could help? Thanks.
use point at parameter where 0 is the startpoint of the poly curve and 1 is the endpoint
now create a circle at point 0
create a square at point one
create your swept blend
Hi Marcel, Thanks for your rely. I only know the profiles at point 0 and at Point 107, and the Swept Blend in Revit not allow multi curve, that’s why I joined the multi model line in a single polycurve.
So you are attempting to use this line (grouped curves -> polycurve) as the path for sweeping between two different profiles? Your background preview looks like the path is flat in the Z direction, correct? Can you sketch the final intent and post a pic? Then we can offer the best advice 
Hi Ewan, Thanks for your rely. Yes, you are right. I will model a bridge with different profiles between start and end points. Thanks for your help.
CurveJoin.dyn (12.4 KB)
Contral Line_Bridge.rvt (1.1 MB)
You will need to first order your curves, then place profiles at points along the reference Polycurve, before creating a solid. I have demonstrated this with Circle profiles to make a ‘horn’ using your layout curve.
Good luck! 
Post back with how you got on after you have tried to implement this for the benefit of others on the forum. 
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Hi Ewan, Thanks for your help. In my case, I only know the start and end point section profile, I don’t know the mid cross section profile. The attached two cross sections profile maybe a bit complicated, but I even used two very simple hexagon and circle cross sections, it still doesn’t work.
Slab_Sec_1.rfa (528 KB)
Slab_Sec_2.rfa (320 KB)
Try using the node PolyCurve by Profile Family Type to get your geometry.
Hello Ewan_Opie
I really want to know how to use this node!
I encountered the same questions…