Grizzly Adams has a video about bridge suspension. Go to his profile and look through the threads he created and I think you will find your answer.
Good looking bridge. Have fun figuring out the width of your bars. I made my father a bridge and he wanted the bars to be wider. He bought wooden dowels and experimented with the width. Start wide so you can see what works best for you. Just make sure to adjust the suspension triangles so the forces are distributed correctly.