Column Stiffeners and Doublers
Column Stiffeners and Doublers
(OP)
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?
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?






RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
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?
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
Are you using the net flange force to check shear in the web?
DaveAtkins
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
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).
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
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.
RE: Column Stiffeners and Doublers
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?
RE: Column Stiffeners and Doublers
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.
RE: Column Stiffeners and Doublers
RE: Column Stiffeners and Doublers
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.