Inverted T-section RC beam design

[Anonymous]

Greetings,

I'm having trouble designing inverted T-section RC beam, example attached below. Since there is no option of such cross-section, in previous post I've seen a suggestion to design the structure "upside down"(example) - does that mean to change the global coordinate system or simply the direction of the loads ? And secondly, when designing T section beam, RSA doesn't put longitudinal/transversal reinforcement in the beam's flanges, by my calculations it's not needed as well, but the standards require the minimal reinf. to be put. So, how do I make RSA design it with it ?

T. R.

[Anonymous]

*Bump* Still looking for advice/solutions.

[Artur.Kosakowski]

Hi @Anonymous

I'm sorry not answering you earlier but in a situation 1 : many (forum users) I may not able to do this as fast as I'd love to and may not be able to do this for all posts however the use of the search option may stand for a good replacement in some situations 

If you run the search for your flange question you will find the answer in the first topic listed:

For the other question that would probably be the same for a single beam model (I haven't tested this so you may actually perform it and decide which works better for you). You may also compare the results to continuous foundation T beam design on elastic soil with very small KZ value.

I hope this helps.

P.S. If you share your findings on the forum I'm sure that would be of great help for other forum participants having  a similar design in the future 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Thank you for your reply, Artur. The flange question came to me while writing the original one, so I didn't check for solutions beforehand (sorry). Now onto the main problem - since I haven't found a way to invert the global coordinate system, would it be correct to design normal RC T beam with the loads distributed on the bottom side of the beam (trying to figure out this "upside down" model thing) ?

[Artur.Kosakowski]

Since I haven't found a way to invert the global coordinate system

You can't do this but what you can do is to define a model as if it was 'reversed'. My main concern is with the provisions for bottom reinforcement which is at the negative 'part' of the local Z axis of the bar and I'm not sure what would work better as in both cases we sort of 'cheat' the program to do what it wasn't designed for. Perhaps the 3rd option will be actually the best? 

[Anonymous]

Hello again,

I've tried a couple of things on this matter:

1) In file (Kelpsa-4) I've used beam model with gamma 180, the program assumed it was a beam with precast slabs cross section, did the calculations and moved some of the bottom rebars along the flanges and the result was still verified as O.K. You mentioned in the previous post that this cross section's design is based on assumption of its being of "quasi" rectangular shape, but it seems like it includes flanges in the calculation as well.

2) In the file (Kelpsa-4(+Z) I've modeled loads in the opposite direction(along the bottom side normal shaped T beam), the needed reinforcement value is the same, but i get 2 calculation errors (e.g. 2 Span P1.Right support. Insufficient bottom reinforcement area near the edge support) and an additional (unwanted) "main-top" rebar (No. 5).

I'd prefer using the 1) option, unless it's incorrect, any thoughts ?