a technique to model a beam supporting slabs from 2 different levels

[dollarbulldog]

Hi

Can anybody suggest the tip to model a beam which must support slabs from 2 different floor levels (one slab at top and another at bottom level of beam). I have tried to use a shell with assigned spandrels but it seems to be clumsy. I have noticed that ETABS allows to assign spandrel label for beam too. How can make it work? Thanks

 

[slickdeals]

I think you are better off modeling a wall element to pick up the two loads. You should be able to get shears and moments for design by assigning spandrel labels. However, you will need to break the spandrel labels into multiple pieces to pick up all the values of moments/shears.

For example, if you assign only one spandrel label, you won't be able to get the positive moment at midspan because the spandrel only reports forces at the ends.

 

[dollarbulldog]

Dear slickdeal
I am using that method you mentioned since i still dont have any better way. It seems to me that the result obtaining from wall element is greatly affected by the way to model slab.

 

[ATOOMUS]

Hi,

Use two separate beams on two different levels then use supper-position method to collect internal foreces or stresses.

Try it then send me your results and conclusions if u can do.

 

[dollarbulldog]

Dear ATOOMUS

This seems to be non-automated procedure and I try to avoid such non-automated procedure in conducting large-scale analysis model. What's your suggestion?

 

[ishvaaag]

You may also put the beam at a one level and pass the loads of the other through notional (non-existent) short columns, likely pinned to beam and floor. You will get then overall forces right for the beam; however when doing these things one must be attent to the actual way of passing the loads to the beam, to avoid some kind of stresses being forgotten, say transversal flexure of a flange etc, that must be accounted for when support so demands. In a case like yours it seems both flanges would be laterally coerced for movement, so it will be more than anything an issue of passing the vertical floor loads. One may also get hypersafe design these ways, since except you specify it, the program may not consider the bottom flange coerced.