Shell Interfaces in RAM Elements

Question

Just getting the hang of Elements and was trying to model a shear wall in a steel frame and I am having trouble figuring out and applying the shell interfaces properly so the wall only attracts the in-plane lateral loads and not the vertical loads from the beams and column. I have tried a few combinations but the vertical loads are still be being transmitted to the wall and not thru the beam and columns that the shell is bordered by.

Karl G · Accepted Answer

Please refer to the attached model. The frame on the left consists of a steel moment frame with a concrete wall. A Type 1 shell interface is modeled, which will allow only shear transfer across the interface so that gravity loads are resisted by the steel frame and the lateral loads are dragged into the stiffer shell. The frame on the right is the steel moment frame only, and is modeled to compare forces with the frame with the shell interface. Each frame is modeled with a vertical 2 kip/ft distributed load along the beam and a 10 K lateral load a the top of the frame. 
 When viewing shears and moments in the beam and column, you will see that the forces in the frames are nearly identical (differences due to the gaps associated with the interface). The screen capture below shows the moment diagrams for each frame. 
 
 The sum of the TX reactions at the finite element nodes at the base of the shell equals 10 k, which shows that the entire lateral load is dragged into the concrete wall. 
 
 1.37 + 1.52 + 1.61 + 1.55 + 1.42 + 1.23 + 1.29 = 9.99 k 
 Shell Interface Example.etz

Karl G · Answer

Lauren, think of the interface as a gap between the frame and the shell. The interface type controls which forces are exchanged between the frame and shell across this separation. The 4 nodes correspond to the beam and column interface sizes that are entered when the interface is created. If 0.5 in is entered for both, then an intermediate node is created at a distance of 0.5 along each measured from the beam-column joint to facilitate the interface. The shell is meshed to nodes that are offset 0.5 in from the beam and column in that case and not to the intermediate finite element nodes that are added along the beam and column.