If your applicable code is ASME B 31.3 Ed 2004 or later, you can use App-P - toggle on it's implementation in Caesar-II 5.00 or 5.10 config in 'SIF & stresses' heading. Calculate operating stress & compare with allowables & defend your design.

But, be careful, loads on your supports will be high & the same need to be properly designed with co-ordination with civil/structural.

Support spans & allowable displacements are suggestives & can be violated without violating allicable code. With high mid-span sag, there may be need for high slope for draining.

regards,

sam