Combination of steel grades in one section

[formi]

Hello everyone!

I wonder if it's possible to compose a section made of wide flange column in 65 ksi with welded cover plates in 50 ksi? How to calculate its compressive resistance when there are 2 grades within one section? Any other things that I should be aware of when designing such a section?

 

[CELinOttawa]

As best as I am aware, you need to remain within the capacity of the lower strength section when dealing with a column, with the exception of some possible advantages for moment frames or other bending situations. Very large beams can be built of different strength sections in order to take advantage of the higher strengths for flanges or webs to handle disproportionately large flexure or shear.

It is easy to see how this works when designing elastically, but becomes a bit more complicated when trying to address plastic design.

I wouldn't do this if I could avoid it, and I would be looking for specialist support from the Steel Solutions Centre, HERA, or other industry expertise. Contact the appropriate industry resource for your area of practice; They are frenquently only too happy to help, and nearly always for free or nearly-free!

 

[rb1957]

keeping to the lower strength is conservative.

the more detailed approach is to check both materials. it's all straiing at the same rate, just part A is limited to 50ksi and part B 65ksi. i think you need to be careful is selecting loadcases to make sure you're loading up the weaker material as much as possible.

another approach maybe to allow/permit the 50ksi to yield and hope that the 65ksi material with restrain it and carry the load required.

another day in paradise, or is paradise one day closer ?

 

[structSU10]

I would imagine the column would buckle before the 65 ksi strength makes any difference, if that is all it is being used for. If it is combined bending and compression, maybe it will make a difference. You would want to understand slenderness of each component, and if you need to account for plasticity, its kinda funky but could be calculated. Of note, the 65 ksi likely has much lower ductility than the 50 ksi steel, which is something you may need to consider.

 

[KootK]

Really, even when you specify the same grade of steel, it's a bit of a lie. Consider:

1) Your wide flange section starts going plastic first at locations where Fy is effectively reduced due to residual stress patterns. Your plates, on the other hand, don't really have any residual stresses.

2) If the wide flange is an existing column, there will be locked in compressive stresses in it unless you're able to jack the supported structure to relieve the stress in the column.

Is this a new member or a reinforcement for an existing column? I have a handy cheat if it's an existing column.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[formi]

It's a new member.

 

[CELinOttawa]

Kootk: Wooten FTW!

 

[KootK]

@CEL: I feel as though I may be missing some important cultural reference here. What is this "Wooten" that you speak of?

@Formi: two practical points of interest:

1) When your welds cool it will wreak havoc on the cross section residual stress patterns. As a result, there's little point getting too fancy analytically unless you're desperate for capacity or there're a thousand of these things. Just use the lower Fy.

2) Keep an eye on how the compressive load gets delivered to the combined section. If the load isn't applied uniformly to all the parts, you need to quickly get an appropriate share of it out of the wide flange and into the plates at either end of the member (heavy local welding). I only point this out because I've seen it missed a few times in the past.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

@CEL: Jim Wooten's 3rd Law! Got it. New information for me -- thanks.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

I've always wanted a copy of the first and second laws... It is rumoured they exist as a 1960s paper memo. Pre-internet, pre-ladies, and pretty aweful.

I was just showing my two interns (one male, one female) "The Honeymooners". They couldn't believe the jokes, nor believe that the audience was laughing as Ralph threatens to hit Alice. We have come a long way, and most all of it very good... So far that the youth today don't even believe you when you mention the "old norms".

 

[KootK]

Now that Ray Rice has actually attempted it, threatening to knock your spouse "to the moon" sounds pretty nutty.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

Everything about hitting another person is nutty, regardless of gender.

 

[rb1957]

1) part of the "humour" might be in it being so inappropriate ?
2) maybe the audience laught is canned, perhaps emphasising that this is meant to be taken as a joke ?
3) so many things we did, said, thought "back in the day" are so inappropriate now, but back then we didn't have anything like "Sandy Hook" (let me emphasise, no disrespect intended)

another day in paradise, or is paradise one day closer ?