Sudden Failure in Beam
Sudden Failure in Beam
(OP)
Hi! Have anybody here encountered concrete design problem, where your steel is yielding and and you cannot increase the size of your concrete section anymore resulting to the most-dreaded "sudden failure"? Thank you very much.





RE: Sudden Failure in Beam
Shear failures tend to be more sudden and therefore have the lower φ factors.
Can you say more about your situation?
RE: Sudden Failure in Beam
RE: Sudden Failure in Beam
RE: Sudden Failure in Beam
RE: Sudden Failure in Beam
Steel yield is assumed for concrete beam ultimate strength design. Just because the steel yields doesn't mean you have a failure (although you will get cracking), although you're best off staying away from it. Concrete crushing is the failure point.
It sounds like you need to tell the client that the beam was designed for a certain load and their new loads cannot be added and keep within code allowables. Making a client happy doesn't mean jumping through unrealistic hoops.
RE: Sudden Failure in Beam
Glass fiber will not strengthen the beam, it will only change the character of the concrete until it cracks. Then you have the steel reinforcing providing all the tensile strength for flexure and shear.
Bonded external FRP provides tensile strength. If the design meets ACI 440.2R-8 design guidance, then there should be no issue with "over-reinforced".
Consider higher strength reinforcing steel, but be aware that over 75/80 ksi (500/550 MPa) you could have serviceability issues (wider cracks or more deflection at higher elongation under load) as the tension force approaches capacity.
If the beam size is not negotiable, and you have maxed out the reinforcing in both the top and bottom of the beam, and have looked at redistribution of moments, then you need to look into significant redesign. I have very seldom seen a beam which can't be made larger in some direction.
You might also consider post-tensioning, internal or external.
RE: Sudden Failure in Beam
If it is badly over-reinforced, then it is the same no matter what tension reinforcement type is used. FRP or prestress will not help you.
The only solution as suggested above is more concrete and depth is more efficient. Tell the client you need more concrete depth (and do not forget that you compression reinforceemnt must be fully tied as for a column, and as concrete strength increases these rules become much more onerous)!
RE: Sudden Failure in Beam
You haven't really given enough information to know if this is a viable solution.
I don't think 50MPa is generally regarded as high strength these days.
RE: Sudden Failure in Beam