Reinforcing Steel Columns 1

[dik]

When I'm reinforcing slender steel columns, I usually run the plates from toe to toe of flanges and extend the reinforcing to 1' from the connections at top and bottom. I design the column with the KL/r based on the new plated section and ignore the 1' at each end figuring that Fy*A will govern (pin-pin condition). I check both conditions (buckling and squash).

Does anyone have a more refined approach to this? Rather than a 'meatball' calculation, I'm looking at doing an SMath program for it.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Agent666]

Dik, it's been a while since I watched this AISC presentation, so I'm not 100% sure on content. But I think the speaker covered this scenario.

https://youtu.be/xltavaJQaGg

 

[human909]

What exactly are your concerns with this 'meatball' calculation? If I understand it correctly it seems the rational approach.

To put it another way is there any way that you think you approach is overconservative or underconservative?

 

[Agent666]

It'll be slightly unconservative as you're overestimating the buckling capacities if we're just talking axial load and no bending. By how much obviously depends on the ratio of extra stiffening required for a given situation.

 

[BAretired]

Columns with variable stiffness can be analyzed using Newmark's Numerical Methods. Also this specific case is addressed in "Theory of Elastic Stability" by Timoshenko and Gere. I don't think 1' at each end will result in any appreciable difference.

BA

 

[dik]

It is a rational approach and I've used it for 50 years... I'm just wondering if there is a 'better one'. The one foot at each end just keeps you away from messing with existing anchoring or bolted beam connections. Thanks Agent666, I'll look at it tomorrow. My design approach is that I design many columns with slight end moments as pinned with no end moments... you just have to be a little careful and understand what you are doing.

Thanks BART... I'm familiar with Timoshenko and was looking for something less...

The column in question has a new jib crane attached at 2/3 height and that moment will be accommodated as a beam column.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[human909]

I don't think 1' at each end will result in any appreciable difference.

Exactly. That was my implied point. A reduction in stiffness proximate to a a completely unstiff (pinned) connection quickly becomes negligible.

Sure the next question might be we how negligible is negligible? Well I put that into the same basket as all the other minor assumptions we make, eg pinned connections that aren't perfectly flexible.

We could quantify the 1% but is it really worth the effort?

 

[dik]

Thanks... my sentiments... I was wondering what the effect was...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

I'm with human909 on the scale of the impact. The effect of not reinforcing the last 1' may well be on the order of not accounting for shear flexbility.