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Question about adding steel members to a strucuture

Question about adding steel members to a strucuture

Question about adding steel members to a strucuture

(OP)
I have an equipment support structure that I am working on. There was an issue in the field and now we have to shift the beam forward to avoid clashing. I have attached the original drawing along with the new drawing showing the change in the structure. Bracing has been added to the structure in order to help support the new over hang due to the shifting of the beam. The bracing I am using are double L4 x 4 x 3/8 angles. The over hang length is 4'-8". I have run a STAAD analysis on the structure and found that the member all pass including the new braces (all with stress ratios less that 0.9). I am checking the base plate to verify that the additional weight and wind load do not effect the base plate thickness. I believe that a 3/8" thick plate will be adequate for the angle connection. Since both the plate and the angles are 3/8" thick, I believe a continuous fillet weld 3/16" size should work along with two 3/4" diameter bolts at each end of the brace. What else should I check? Is there anything else I am missing. Any comments/suggestions are appreciated.

RE: Question about adding steel members to a strucuture

To me the drawing is a bit confusing as it doesn't separate mechanical/electrical from structural. As far as your STAAD model goes......keep in mind: for braces, you have to check them manually as STAAD's code check is based on a concentric loading. I believe AISC has tables for that (I have some of my own).

EDIT: By the way, it appears you have that brace coming into a HSS wall. I don't know how much force we are talking about.....but if it's a significant amount, you may need to check the wall for it.

RE: Question about adding steel members to a strucuture

(OP)
The force coming in to the wall is 6.9 kips. I check the weld strength A 1/4" size fillet weld is adequate.

RE: Question about adding steel members to a strucuture

he means you need to check wall plastification per chapter K of AISC.

RE: Question about adding steel members to a strucuture

I think WARose meant that you should check the wall of the HSS for plastification and punching shear per section K of the steel manual.

RE: Question about adding steel members to a strucuture

(OP)
Is there an example of that calculation check of wall plastification per chapter K of AISC available?

RE: Question about adding steel members to a strucuture

Yes, AISC publishes detailed examples for most of their calculations.

RE: Question about adding steel members to a strucuture

(OP)
Also, I checked the base plate for the structure since we added bracing to it. I am getting that I need a thicker base plate then what is shown in the vendor drawing. The base plate is shown is 1 1/4" but with 36 ksi grade steel I am needing 1 1/2" thickness. I believe adding stiffener plate will help resolve the issue, but I do not have a program to back it up. Any recommendations.

RE: Question about adding steel members to a strucuture

Stiffeners probably would help with the material thickness of the base plate but be sure to consider the economics of that. If the base plate has not been fabricated, then using a thicker plate will likely be cheaper than adding the stiffeners. If the base plate is already welded on to the equipment, then stiffeners may well be the way to go.

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.

RE: Question about adding steel members to a strucuture

Quote (OP)

I believe a continuous fillet weld 3/16" size should work along with two 3/4" diameter bolts at each end of the brace.

I wouldn't consider the bolts and the welds as acting concurrently. That said, I'm sure that the welds are fine on their own.

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.

RE: Question about adding steel members to a strucuture

Anchor bolt capacity and possibly the foundation itself need to be checked for the revised loading. This may not be your responsibility; just see that it gets done. You are making changes, but does the foundation designer know that? A high percentage of failures are not because of design flaws or structural defects, but because something that basic gets overlooked and "falls through the cracks".

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RE: Question about adding steel members to a strucuture

(OP)
@SlideRuleEra - I will check the foundation design and anchor bolts. Thanks.

To everyone else, thank you for your input.

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