Simply supported Pedestrian bridge with two tube arch at both sides

I am modeling simply supported pedestrian bridge which have 2 architectural arch at both sides.

My questions are :-

1-What are the possible ways to draw arch in Staad Pro??

2- How to make Staad Pro understand that it's not structural element but it will effect it's behavior?? 

3- Could i put both of models in one model containing the bridge body rested on Elastomeric bearing at both ends on the towers ??

I have attached the two models with the AutoCAD file for more clear understanding of the bridge.

Please help me ASAP

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