RC Beam with Set down Analysis and Detailing 3

[ENGUCR]

For a heavily loaded power station, A girder beam having a 500 mm set down is required to design(refer attachment). This girder is also supporting spandrel beam exactly at the set down location. The design procedure that I have followed for this non prismatic beam is as follows
1. The beam is modeled using frame element as a sub frame.
2. Two different frame elements are defined for the different two sections and they are combined using insertion points & thereafter loaded the beam
3. Analysis results are obtained and the bottom flexure r/f are derived using the 750 mm(D) dropped section & continue through out the bottom
4. Top r/f at restraint ends are also calculated for respective sections(1250 and 750 mm D)
5. Links are calculated from the analysis results at both ends for respective sections while provisions are made for the hanger links also
6. The Detailing is done as given in the attachment

Please comment if there are any more considerations on analyzing, designing and detailing to be done for these kind of beam sections
Thanks in advance

 

[ENGUCR]

Thanks jayrod12 and KooTK
@KOOTK:
Yes. I understand what is going on. Section dimensions seem to be not adequate to provide such a fixity and control the deflection. So I will retry with jayrod12 method with increased beam depth

But based on the levels, I would suggest to implement following arrangement to the beam. What would be the feasibility of this implementing this arrangement than using earlier arrangement. What minimum value of x will make this beam, equivalent to a simple one level beam or otherwise will this arrangement will behave in a different way. Note that the Depth(D) will be in the range of 750 mm-900 mm

 

[Tomfh]

To get the comparable strength you need to make X at least several times the beam depth. I like your first drawing better.

 

[rapt]

I would prefer a 30 degree slope on the bottom rather than the 45 degree shown.

The diagonal thickness through the throat of the step needs to be the same as a the beam depth. This will give you full capacity using the same reinforcement.

 

[slickdeals]

Unless the additional headroom is needed on the left side of the beam, it is simpler to keep the bottom level the same all the way across. You'll have a bit more concrete, but the reinforcement detailing and formwork just got a lot more simpler.

 

[KootK]

What minimum value of x will make this beam, equivalent to a simple one level beam or otherwise will this arrangement will behave in a different way.

I think that you're almost there as you've sketched it. In more detail:

1) I would proportion the joint following rapt's advice regarding maintaining your flexural depth throughout the joint.

2) I would take the center line length of the beam, including the diagonal bit at the step, and stretch it out to represent a faux, slightly longer beam.

#2 probably isn't a big deal but I'd include it simply to acknowledge that fact that there's no such thing as a free lunch. Introduce some goofy step, get some additional deflection (of course). #2 is a simple way to account for that without getting a headache.




I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Tomfh]

If you simply maintain the depth and reo through the joint won't you risk having less than 100% capacity of rectangular beam? I.e. can you really assume beam theory is valid at a kink?

 

[KootK]

f you simply maintain the depth and reo through the joint won't you risk having less than 100% capacity of rectangular beam? I.e. can you really assume beam theory is valid at a kink?

A large value of x as you've proposed would be ideal I think. And I agree that Bernouli beam theory gets more dubious the smaller we make x. That said, there are ways to deal with the "disturbed region" that results from a small value of x other than Bernoulli beam theory. One simply has to choose a path and then walk it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.