I am designing a structure with steel truss supported by concrete columns, performing the analysis and design, I already have the right sections for every members. And since I am designing now the connection (truss-concrete column), I needed to delete the concrete and retained the truss and added pinned supports just to get the reactions in the truss support. However, when I ran again the analysis and design, I noticed the utilization ratio of most members of my truss became lower as when it was combined with concrete structure. Which is correct way of designing this, design the two separately or in combination?