column to existing beam connection

[LAU668]

Hi FOLKS;

I am designing a project. there is a new column stand on top of existing beam.
the column is w12x45, exiting beam is w36x135.

I don't want weld stiffener on the exiting beam. the beam is 80' long, huge load on top of it.
anyone have idea of it?

Thanks

 

[BAretired]

If bearing stress is within limits, stiffeners are not required. Are the column and beam webs aligned?

BA

 

[LAU668]

column and the beam webs aligned

 

[LAU668]

can i design column base plate thicker? use 1" base plate.

lAU668

 

[KootK]

can i design column base plate thicker? use 1" base plate.

Sure. However, if your webs are aligned, I would think that there wouldn't be much to be gained that way as you're already spreading the load out over the depth of the column. You'd probably need base plate stiffeners to make substantial gains.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[njkeng]

I agree with the above comment. If you don't want to add stiffeners to strengthen the bearing capacity of the web in the existing beam, you should increase the 'spread' of the column reaction into the beam web by increasing the bearing area with a larger column baseplate incorporating base plate stiffeners between the edges of the column and the baseplate to limit the flexibility of the baseplate.

 

[LAU668]

thanks kootk & njkeng;

I got it

 

[BAretired]

Using a doubler plate each side of the column web may be worth considering to increase bearing area of the column as its web is less than 3/8" thick. The width of bearing for the beam can be as much as 2k which is more than 3".

BA

 

[KootK]

BA's suggestion might also be a good way to ensure that there truly is some overlap between the webs in the field. Assuming perfect alignment is always sketchy, especially in a reno situation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[LAU668]

Can I design a pre-welded stiffener part?
see attached picture.

 

[CELinOttawa]

Yup; That'll work... The web cannot cripple like that; I might think about cross bolting through the web to clamp the assembly together and eliminate the chance of the three pieces parallel to the web from opening.

 

[KootK]

Clever concept. I wouldn't be comfortable with it personally, however. I worry that bolt slip would mean that the column web to beam web load transfer path would be much stiffer than the pre-welded stiffener path. The beam web would then attract the lion's share of the load and you'd still have to contend with web yielding and crippling. I might go for it with slip critical bolts but, even then, I'd be a bit nervous.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

KootK, Assuming the governing failure was crippling as opposed to yielding you don't think that detail would assist much? I agree that i would rely on the original web only for terms of yielding as per the stiffness load sharing you mentioned.

I would think that the vertical plates, if spaced close enough over a region would resist the ability to buckle in many ways. Just wondering your opinion

 

[KootK]

Assuming the governing failure was crippling as opposed to yielding you don't think that detail would assist much?

.

I do agree that the assembly would prevent any buckling tending to occur beneath the columns flanges. The question for me, I guess, is do I believe that's where the buckling wants to occur in this situation? I'm not sure that I do. I see the reaction beneath the column as being more like a uniform load beneath the web of the column, skewed towards the flanges. And, if that's the case, how do we know that crippling won't occur at the center-line of the column rather than at the flanges?

This one would be out in no man's land for me. If it were my project and a designer brought me this solution, I'd request something else. If I were reviewing a colleague's project and came across this detail would I go to the mat arguing for it to be changed? Nah.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[LAU668]

Hi CEL;

is your opinion like the attached picture?

 

[SAIL3]

do not understand why the OP does not follow njkeng's idea, unless there are other restrictions, as it DIRECTLY addresses the problem of web cripling of the beam , ofcourse, not knowing the load in the col one does not know to what extent that a problem exists...

 

[BAretired]

What is the factored column load?
Has the column changed from W12x45 to W14x61?
Are you concerned about beam web crippling, bearing stress on column or both?

I have the same concerns as KootK. Pre-welded stiffeners may prevent web crippling of the beam but they would not provide reliable bearing under the column flanges due to bolt slip.

BA

 

[dhengr]

LAU668:
I agree with KootK and BA and will try explaining Njkeng’s approach, as I understand it, in different words. His idea was my thought too. Lengthen the column reaction area, down the length of the W36 to reduce the web bearing and crippling potential. A W14x61 col., means d = 13.89", say 14", and I would extend your col. base pl. 8 - 10" beyond each flg., a 34' long col. base pl., down the length of the beam. Weld .5 or .75" stiffener pls. btwn. each col. flg. and the base pl. on the line of the col. and beam webs. This transfers the flg. loads down the beam length and lessens crippling and bearing stresses per unit length on the beam web. My sizes are for descriptive purposes only, since you haven’t told us anything about the loads, moments, etc. I might have some less concern about some light welding on the beam, above its neutral axis, if I could do some min. jacking and shoring under the weld area. Then some half height stiffeners might be put under the col. flgs. and fitted for bearing to the underside of the W36 top flg. Maybe 4" wide, 12-16" high x 5/8" thk. (4 thus).

 

[CELinOttawa]

Yes, particularly for the through bolting.

I do, however, think some of the other posters have raised pertinent points, particularly Kootk and BA. You will need to address them to your satisfaction before you proceed...

Don't forget that your drawing shows these stiffener assemblied perfectly tight, but you need to be able to build tge darn thing! Perhaps opposing shims for the top packer?

 

[SAIL3]

dhengr has explained it pretty good.....one other concern I would have is the possibility of weak/weak axis instability in this area...I would consider the col pinned in the weak direction @ the beam and the possibility of the beam fla rotating....maybe some partial web stiffeners on the beam to address this...if there are other tributary bms tying in and around this area, it may be less of a concern.....