Hi all,

Newly grad and newbie to Risa :)

I need to check the capacity of junior beams supporting a monorail at their midspans.

Modelling the junior beams are simple enough (about 6 beams spaced at 5.5ft), but I'm stuck at trying to model the monorail (S10x50) supported by the junior beams at their midspans. The monorail beam should be "hanging" , but modelling it just makes the beam cut "through" the supporting beams like a horizontal bracing. Is this the correct way of modelling it?

Any help would be appreciated

It depends on what you're trying to get out of your analysis. Most of the time, you are concerned primarily with the vertical load that the monorail transmits to the supporting structure. If this is the case, then modeling the monorail and the supporting beams at the same elevation is fine.

If, however, you are primarily concerned with lateal loads in the monorail (and how this can cause moment in the supporting members) then you could model the vertical offset between the two members. There is a section in the Modeling Tips section of the RISA-3D help file which talks about using rigid links to model one beam crossing over another. I believet that is similar to your situation.

JoshPlum is absolutely correct...you would model your junior I beams and locate nodes in the XZ plane where the S10x50 crosses them, then relocate your grid (or manually) draw in the monorail beam with nodes again in the same XZ points but with the neutral axis lower by 1/2 the depth of the junior I beams and 1/2 the depth of the S10 connected vertically by rigid links.

You can also apply loads to the S10x50 either by using the "moving load" module of RISA or by suing rigid links to simulate the vertical offset.

A secondary check would be to look at the flange loading per the Crane Manufacturers Association of America spec #74.