Limiting stress value for steel beam flanges in composite sections
Limiting stress value for steel beam flanges in composite sections
(OP)
When looking at a steel concrete composite section you need to calculate the build up of stresses in the extreme fibre of the steel beam's flange. This is relevant under hogging moments but im not 100% sure why.
What sort of failure do you get when the yield stress is reached in the flange? Is it to do with torsion or is literally just a bog standard thing - checking the limiting stress value isnt reached in the beam and I suppose its more relevant as the concrete is cracked?
What sort of failure do you get when the yield stress is reached in the flange? Is it to do with torsion or is literally just a bog standard thing - checking the limiting stress value isnt reached in the beam and I suppose its more relevant as the concrete is cracked?






RE: Limiting stress value for steel beam flanges in composite sections
What is a hogging moment.
For a composite section, you will typically assume the yield stress has been reached in the entire steel section - possibly all tension or some compression and some tension.
What in the world is a "hogging" moment?
RE: Limiting stress value for steel beam flanges in composite sections
In a 'hogging' section you tend to assume any concrete in tension is cracked, which is fine. I was just curious as to the relevance of checking the stress capacity in the flange in particular in these sections.
RE: Limiting stress value for steel beam flanges in composite sections
RE: Limiting stress value for steel beam flanges in composite sections
RE: Limiting stress value for steel beam flanges in composite sections
RE: Limiting stress value for steel beam flanges in composite sections
RE: Limiting stress value for steel beam flanges in composite sections
We don't typically count on reinforcement, but have when necessary.
kslee-
I sort of see your point with buckling, but........
1.) that has nothing to do with built up stresses if the bare steel alone is taking the negative moment. It is whta it is. M/S. That simple there is no need for superposition of stresses since there is no composite section for negative bending.
2.) unless you have stacked construction (e.g. the typical case of beams framing into girders with the same top of steel elevation), the beam framing into the member in question will serve as a brace point for both flanges (assuming the shear connection extends more than halfway down the web of the member in question).
RE: Limiting stress value for steel beam flanges in composite sections
Are you considering the rolled section to be composite with the reinforcing in the negative moment region?
civilperson-
I have used negative reinforcing, for bridge superstructures. For this condition, AISC doesn't seem clear that the plastic neutral axis will move toward the reinforcing and away from the compression flange, making the composite section more susceptible to buckling. That is, a compact rolled shape is not always compact when composite with reinforcing. I think I3.2(b)(1) should read "The composite section is compact, according to Cases 2 and 11 of Table B4.1..."
RE: Limiting stress value for steel beam flanges in composite sections
RE: Limiting stress value for steel beam flanges in composite sections
The compactness of the compression flange is unaffected by the movement of the PNA upward toward the reinforcement. The compactness of the web in compression may be affected, but only in a lesser degree since the height of the compression part of the web divided by the height to the PNA is limiting the ratio of hc/tw.