topic Re: Inverted Beam in Robot Structural Analysis Forum

Inverted Beam

Anonymous — Mon, 07 Sep 2015 20:56:57 GMT

What is the best way to design inverted beam

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

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

Re: Inverted Beam

Artur.Kosakowski — Tue, 08 Sep 2015 08:10:54 GMT

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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Re: Inverted Beam

Anonymous — Tue, 08 Sep 2015 08:46:50 GMT

thanks for your quick answer

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

Re: Inverted Beam

Artur.Kosakowski — Tue, 08 Sep 2015 09:03:44 GMT

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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Re: Inverted Beam

Anonymous — Tue, 08 Sep 2015 09:16:09 GMT

but what about the steel ?

isnt suppose to be reversed?!!

Re: Inverted Beam

Artur.Kosakowski — Tue, 08 Sep 2015 09:48:22 GMT

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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Re: Inverted Beam

Anonymous — Tue, 08 Sep 2015 11:56:57 GMT

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

Re: Inverted Beam

Artur.Kosakowski — Tue, 08 Sep 2015 12:42:59 GMT

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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Re: Inverted Beam

Anonymous — Tue, 08 Sep 2015 15:18:29 GMT

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?

Re: Inverted Beam

Artur.Kosakowski — Wed, 09 Sep 2015 06:38:17 GMT

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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Re: Inverted Beam

Anonymous — Wed, 09 Sep 2015 08:05:18 GMT

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.

Re: Inverted Beam

Artur.Kosakowski — Wed, 09 Sep 2015 08:40:54 GMT

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

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Re: Inverted Beam

Anonymous — Wed, 09 Sep 2015 08:45:29 GMT

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?