Maximum allowable reinforcement strain
Maximum allowable reinforcement strain
(OP)
Hey. So I'm looking at RC beam design, and I'm aware that beams are typically designed to be tension controlled, i.e. at the concrete rupture strain (0.0035), the steel should be beyond the yield strain. I've read that it is good to aim to have the steel strain at around 0.005-0.008 when the concrete ruptures. What I want to know is, what is the maximum allowable strain in the steel? What strain does steel fracture at? I can't find a definitive answer.
Thanks
Thanks






RE: Maximum allowable reinforcement strain
RE: Maximum allowable reinforcement strain
I ran a bunch of different beam configurations and pretty much was always ending up with strains in the 0.0x to 0.00x range so well under the 0.1x range for rupture on diagrams I was finding. It was seeming that the minimum steel ratios and standard equations where set up to pretty much guaranty the steel isn't getting close to the rupture strain when the concrete reaches its rupture strain of 0.003-0.0035 but is hovering around the 0.038 to 0.045 range. See some examples below all with min steel and f'c of 5,000: 8x8, 12x12, 8x16, 12x24, 18x36, 12x120, 48x120
those images got horribly compressed - attached zipfile has the uncompressed images where you can read the numbers.
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
RE: Maximum allowable reinforcement strain
RE: Maximum allowable reinforcement strain
RE: Maximum allowable reinforcement strain
Link
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
RE: Maximum allowable reinforcement strain
pretty much get an es = 0.044-0.045 strain at minimum steel in every case so far.
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
RE: Maximum allowable reinforcement strain
Skin reinforcement starts coming into play though which included or not in anaylsis can greatly impact the steel centroids and help rein that extreme strain back in, although at the expense of shear strength when considered.
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
RE: Maximum allowable reinforcement strain
skin bars
w/o skin bars
Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering
RE: Maximum allowable reinforcement strain
There are no problems with higher ductility reinforcing products such as those used for Earthquake design which are normally in the order of 10 - 15% strain.
But for normal reinforcing steels there are reasons for limits but the design codes do not apply them.
At a minimum reinforcement level equivalent to the cracking moment of the section, the strain in the steel will be in the order of 5%. As the reinforcing level increases, this strain reduces.
If you add the effects of strain localisation at a crack, this strain actually increases so it is significantly higher than 5%.
For the lower ductility reinforcement products like welded wire products, European Class A (at 2.5%), Australian Class L (at 1.5%)these actual strain levels are a real problem and need to be addressed by design codes.
Unfortunately it always seems to be in the too hard basket. The lower the ductility of the reinforcement, the higher the minimum reinforcement requirement should be to account for this.
RE: Maximum allowable reinforcement strain
RE: Maximum allowable reinforcement strain
RE: Maximum allowable reinforcement strain
They are the minimum strain requirements, but Eurocode does not require you to limit strain in the steel due to flexure if you use an elastic/plastic stress strain diagram. You only have to limit the strain if you allow for increasing strain past yield.