Inverted Beam

[Anonymous]

What is the best way to design inverted beam

1. make offset for it to be above the slab.

or

2. normal rectangular beam and in the provide reinforcement choose slab cut ?!!

[Artur.Kosakowski]

This is tricky as the RC Beam design module doesn't support inverted T beams. I'd consider creating a model of a slab "upside down" as if the beam was under the slab and then follow the workflow described here:

http://forums.autodesk.com/t5/Robot-Structural-Analysis/T-slab/m-p/3185418

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Beam-offsets/m-p/3332921

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[Anonymous]

thanks for your quick answer

but what i have is edge beam so its not helpfull the T beam with me i Think

[Artur.Kosakowski]

Then you may follow the same workflow calculating IY as for "offseted" rectangular beam and design it without the change in the cross section. In this case there is no need to model a slab upside down. 

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[Anonymous]

but what about the steel ?

isnt suppose to be reversed?!!

[Artur.Kosakowski]

The rebars are generated where they are needed. For the T beam and "upside down" model in the RC Beam design module you will see the flange at the top but you know that in reality it is at the bottom of the beam. For the other scenario (edge beam) if you don't define the model upside down what is top is top. If you do then what you see as reinforcement is also "reversed". 

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[Anonymous]

what about the first proposal , is it will work?!!!

[Artur.Kosakowski]

This cross section is not intended for use as a reversed T shape but for a beam with precast slabs instead and the design is based on assumption of its being of "quasi" rectangular shape (flanges are to support these precast slabs only and are assumed as being short). 

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[Anonymous]

So the best proper way is to increase IY for the edge beam and design it as Rectangular shape and assume that the steel at the bottom is actually will be at the top and the top steel will be the bottom in actual , right?

[Artur.Kosakowski · Accepted solution]

Correct in the situation when you defined your structure "upside down" which would only be the case when you want to design reversed T beams. If not, you can model a structure as usual > increase IY of edge beams > design rectangular beam with bottom reinforcement being the bottom one and top the top one. 

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[Anonymous]

You mean "If not, you can model a structure as usual > increase IY of edge beams > design rectangular beam with bottom reinforcement being the Top one and top the Bottom one.

[Artur.Kosakowski]

No, bottom being bottom and top being top (for not reversed model - see the attached picture).

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[Anonymous]

this is right if i reversed the model , but we agree that no need for that .

so if no need i will increase IY and design Rectangular but the steel in real will be reversed . am i get it right?