Column Stiffeners and Doublers

[iponom]

Question from my partner, resulting from questioning the importance of considering the direction of lateral moments along with gravity moments versus the load combination (i.e. the total moment).

Consider you have gravity moments and lateral moments for beams on two opposite sides of a column. The beams are directly welded at the flanges. I find that I need a column doubler and a stiffener by comparing the flange forces with equations in AISC Manual, Sect. J10 p.16.1-115-120. When I design the doubler thickness I consider the shear capacity of the column as "Web Panel Zone Shear" p.16.1-119 and the shear transfer from the stiffeners as described in AISC DG13 p.29

Q1. Is that a correct procedure?
Q2. If I find that we don't need a doubler when comparing "Web Panel Zone Shear" to the required shear, and need stiffeners for Web Local Yielding, would I need to consider the shear transfer from the stiffeners to the col web., why not?
Q3. Why do I need to consider the shear from the stiffeners when designing the doubler?
Q4. How are the Web Local Yielding and Web Panel Zone Shear different?


Currently I design the doubler for both shear forces as described above, and when no doubler needed I don't design the column for shear from stiffeners, but still design the stiffeners for shear at the column web and their respective welds.

Q5. When designing Column stiffeners and Doubler is it important to consider the direction of the lateral loading?

 

[Berniedog]

AISC has a great spreadsheet called "clean columns". I know it is free for AISC members. Also, check out their Design Guide for strengthening columns due to Moment Connections.

 

[iponom]

Clean Columns is not too helpful since I need to perform an analysis on the column due to forces and select the appropriate stiffener doubler size, which clean columns does not show...

 

[westheimer1234]

i just use descon.. =)

 

[iponom]

westheimer1234,

Descon has some bugs in the calcs, which are still unexplained to me... For example when figuring out the stiffener welds LRFD method is used, but I am running and ASD version!!! Question, can you enter Lateral moments into descon?

 

[iponom]

Not to bring down descon, it is an awsome program and idea, I am just not so trustworthy when it comes down to specifics of load application and job which descon does not compute for. And too many bugs, crashed on me like 1000 times already...

 

[westheimer1234]

you can bring that "bug" to their attention.. you can call them.. i did this once.. and they will send you updates.. because sometimes you are using lower version/updates..

 

[DaveAtkins]

I won't try to answer all of your questions, but I will say that in the situation you are describing, doubler plates are rarely required (which is good, because they are expensive). You would need large, unbalanced flange forces to cause the need for a doubler plate.

Are you using the net flange force to check shear in the web?

DaveAtkins

 

[westheimer1234]

i read that too that doubler plates are rarely required.. but in my experience in oil and gas EPC.. it aint rare..

 

[abusementpark]

Why would you need a doubler and a stiffener? Is doubler on the web or flange of the column?

 

[iponom]

DaveAtkins,

You are right about unbalanced forces however that does not answer the question of when I need both would I design the doubler thickness using the shear transfer from the stiffeners...


westheimer1234,

no doublers are required for this job, but I am developing a way program which will figure that out so I need to know the answers to these questions, and so far I am going with DG13.

abusementpark,

Doubler on the web of column. Need it when column web shear is insufficient due to concentrated flange forces out of whack... for example one side 400k the other -200k (V=200k).

 

[iponom]

So far I have formulated a very comprehensive formula, but want to make sure it works before submitting for PE stamping. Oh well thank you for all your replies. I will make this work one way or the other!!!

 

[asixth]

I am very interested in the post and apologies for not being able to comment earlier because the detailing of steel moment connections is a widely debated topic in our office currently. I have seen moment connections go out with diagonal stiffeners, without diagonal stiffeners and have seen someone consider using doubler plates (recommended in the latest Australian rigid connections manual).

Personally it is my belief that diagonal stiffeners and double plates are not required and have built up a quick design example to display my thoughts.

Considering a 410UB53 frame (W16x36) with unbalanced moments. After the change in flange forces have been calculated and the resulting tension and compression diagonal stress determined in the web panel, the stress rarely exceeds 100MPa (14,500psi). Seeing that the allowable shear stress allowed in a web is 120MPa (17,400psi) to Australian standards (unsure about AISC), I do not see the need for diagonal stiffeners or doubler plates.

Please note that beam shear and axial forces have been ignored for the calculations.

 

[iponom]

asixth,


I am a designer in US and I have to deal with AISC steel design manual. I have never used Australian design standards. However I agree that with the appropriate column section one would not need any stiffeners or doublers. It is only when you consider the column limit states in local flange or web yielding, crippling, rupture, shear etc. that you can determine if the capacity is sufficient for the given loading.

I really like how you modeled the column cross section as a truss, I think that it is more appropriate way to do it.

However I was wondering, what other design checks do you use? Is the stiffener in you example welded at the col. web?

 

[asixth]

For the example that I have shown a stiffener plates would be full strength butt welded to the columns, I would match the size of the stiffener plates to the size of the beam flange, this would allow a much more direct load path for the flange forces.

Other checks include:

BEAM WELDS
-Design capacity of flange welds to beams
-Design capacity of web welds to beams
UNSTIFFENED COLUMN
-Local bending of column flange at beam flange
-Local yielding of column web at beam tension/compression flanges
-Column web crippling at beam compression flange
-Column web compression buckling
(These items should be elimanted with the transverse column stiffeners at both the compression and tension flange)
-Column web panel in shear
COLUMNS WITH DOUBLER PLATES
-Local bending of column flange at beam tension flange
-Local yielding at column web at beams flanges
-Crippling of column web at beam compression flange
-Compression buckling of column web
-Shear on column web panel

These checks were all taken from the Australian Steel Institutes publication on detailing rigid connections. I generally detail portal frame industrial buildings where the gravity loads (roof) are quite small and lateral moments (wind) can be significant. Often causing reversal of moments at the beam-column connection.

I am in favour of using transverse column stiffeners but don't think that doubler plates or diagonal stiffeners are required.

 

[iponom]

Here is a sample from my design criteria. Please answer the questions at the top if possible, thanks!

 

[hernestyoung]

I use Descon as well

Anyway, my advice is to ask opinions to expert. You can find one of my supplier following the link below, just ask them, they are usually too give this kind of information free of charge.