I tried to draw a more simple section lines after the studied the models of the structure V and VI. The model created this time was very rigid at the vertex, it was an unexpected result when drawing in the computer model. But there was also a weak point at this structure after I tried to make the loading on the other part of this structure. I tried to figure out how to improve the weakness of this structure. Adding a triangle face at the weak point or other? After trying for many times, I figured out the weakness point of the structure will become stronger if we let the valley of the structure deeper.