Beam Design

[zahr4]

HELLO

I hope somebody can help me with this design problem.
I want to design two beams in which the first beam can take M=192 kN.m while f'c=25 Ma and the second beam can take up to M=219 kN.m and f'c=55 MPa. But the cross section is rectangular section (w=200mm,d=300mm) for two f'c which are 25 and 55 MPa and both need to have the same bar reinforcement. Bars up to 25mm diameter is allowed clear cover is 19 mm and finally fy=550 MPa.
I used ACI method under reinforced case with neglecting the safety factors and I also tried over reinforced case but I got nothing because with under reinforced and f'c = 25 MPa the bottom bars wont yield if I use four 25 mm bars (each two bars are bundled ) but it works for f'c=55. how do u think I should design it?

(please forgive my poor English.)

 

[jayrod12]

All beams must be under-reinforced to force ductile failure modes. Therefore if your beam when analyzed with 25 MPa concrete doesn't yield, you need less rebar or a higher strength concrete. No way around that.

That's a pretty shallow beam to have over 200 kNm of moment on it. What's the span and loading look like?