Bracing joist bottom chord from bottom surface of chord angle.

[StrEng007]

Has anyone run into a condition where they are trying to brace an existing joist bottom chord but cannot place their angle along the top of the existing bottom chord (due to obstructions)?

Instead, I'd have to provide my angle to the bottom of the chord as shown in red.

I'm hoping the GC can run a weld across the full width of the reinforcing angle. I'm just not sure how I feel about the connection not having positive bearing at the chord.

 

[CDLD]

I see no issue.
In fact the red detail is more optimal when considering brace eccentricity to the bottom chord.

 

[human909]

Agreed.

Members bearing on other members is overrated by young engineer and design drafters. For many steel connections bearing is inferior to bolting and welding which often can put the load path in superior places.

The second detail in red seems superior. Marginally harder to install but a few clamps fixes that. Overhead welds are a pain but can likely be avoided if welding the ends is sufficient (which is likely)

 

[jerseyshore]

Any welder would prefer to avoid an overhead weld so your angle in red looks good to me.

 

[StrEng007]

For many steel connections bearing is inferior to bolting and welding which often can put the load path in superior places.

For the record, you mean suspended or side attached connections via bolting/welding, right? All of these connections would have some form of welds or whatnot, regardless if they were bearing or suspended.

I agree with the benefits of the non-overhead weld and keeping the loading closer to the centroid of the double angles. The reason why I'm asking is because the Steel Joist Institute has issued countless iterations of documents, none of which illustrate bottom chord bracing angles in the underside position. I wanted to make sure I wasn't missing something glaringly obvious.

 

[human909]

For the record, you mean suspended or side attached connections via bolting/welding, right? All of these connections would have some form of welds or whatnot, regardless if they were bearing or suspended.

If by 'whatnot' you mean bolts then yes. Sometimes I deliberately design steel constructions to minimise or REMOVE welding. (I work plenty of brownfield sites where hot works are a potential explosion risk.)

Specifically I mean that bearing can often mean loading up the flange rather than the web. In many cases this is neither here nor there. But in other cases it matters. If you actually calculate the additional stress added to a flange through what is likely eccentric loading then it is not insignificant. If the flange is already working hard then this matters.

(This really isn't relevant to solving this question, but can be quite relevant in other steel design.)

The reason why I'm asking is because the Steel Joist Institute has issued countless iterations of documents, none of which illustrate bottom chord bracing angles in the underside position.

I've never read anything from the Steel Joist Institute, and OWSJ of this style are uncommon in my locality. So I'm a ignorant on their advice. However the requirement for bottom chord bracing I understand. Your proposed solution seems structurally preferable, though increase depth which might not be desired in many cases.