How would you model this? And thoughts on lack of diagonal braces?

[damorim]

Hi everyone,

I just want to get your thoughts on how you would model this structure (having some differing opinions within office). Basically, the tank on top is being increased to hold more water and I am tasked with making sure the stand can support it. It is made of 2x2x1/4" mild steel square tubing. It has angle iron bracing at mid-height roughly welded all around. The top (triangle portion) of the stand is also made of the same square tubing welded all around. The bottoms are welded all around to a square plate and bolted with 4 bolts at each corner. See attached pic. Two of the legs are nearly vertical and the third is angled due to space constraints.

(PIC REMOVED)

I will be modelling in STAAD (not a fancy Finite Element) and have limited budget to complete this analysis. Thoughts on setting up model? What supports to use, etc? Also, what are you thoughts on the lack of a diagonal brace connecting the top to mid point to bottom. Looks like a bit of torsion would twist the stand pretty easily?

Thanks

 

[BAretired]

The concept is good. I agree that angles might be easier.

BA

 

[ajh1]

You may find you need to add two more tiers to the bracing, i.e., 3 horizontal cross members top to bottom, to cut down on the unbraced lengths of the tubes. That would also help the angles on the diagonal attachments.

 

[damorim]

Thanks for the suggestions guys. I agree that angle iron on outsides would be the way to go. I just have some issues with how nicely it'll sit on the tubes and what quality the final connection would be. I will likely add two additional horizontal braces to reduce the unbraced length (especially considering if angle will be used for those diagonals). Much appreciated.

 

[dik]

Neat... and even less capacity if you lean on it... a couple of 1/4" rods might help.

Dik

 

[sponton]

Thanks for the suggestions guys. I agree that angle iron on outsides would be the way to go. I just have some issues with how nicely it'll sit on the tubes and what quality the final connection would be. I will likely add two additional horizontal braces to reduce the unbraced length (especially considering if angle will be used for those diagonals). Much appreciated.

Yeah, except that the more complicated you make it [for example, using hss rather than angles as KootK suggested] the more work and cost and not to mention complexity per connection. As KootK also said, the more exaggerated the brace angle the less effective it will be, i would rather add lattice to make sure that the individual tubes are stiffened correctly.

 

[KootK]

I just have some issues with how nicely it'll sit on the tubes and what quality the final connection would be.

Yeah, that's a thing. I'm sure the verticals were not oriented to suit easy trussing. And they're four sided things in a three sided system. One option could be to cope the outstanding angle legs so that the remaining leg forms a tab that can be bent to suit. Another could be to run horizontals inside the legs and then diagonals outside the horizontals. This is a small load thing so I wouldn't sweat the implied connection eccentricities.

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.