OWSJ Reinforcement vs Midsupports

[TORCHMAN]

Working on a project where the loading is being changed on OWSJ members. I plan on proposing 3 options to my client:

1) Reinforce webs - as it stands, I calculated its compressive resistance to be 10kN
2) Add 1 or 2 supports at bottom chords - I didn't think this was an option but saw KootK recommended it on a thread years ago (single support still loads multiple webs higher than 10kN in compression unless more web members are added)[sup][/sup]
3) Add 2 supports at top chord

Below is an image but it is uploading blurry so I also attached it.

Option 1 is a lot of work, also, I will need to check footings.

I am thinking that option 2 is the optimal since the client could get a beam under bottom chord more easily than under the top chord and no modification to webs is required. As I understand it, using option 3, 2 new web members would be required at each OWSJ. Below is a KootK sketch from some time ago showing a good detail for option 3.

Note that there are 2 floors that need to be reinforced.

Base on your experience, what are the Pros & Cons?

 

[bones206]

Just bringing this full circle, it looks like your live loads for the slab and joists have increased by a factor of 2.5. Adding intermediate joists still seems like the best option in my opinion. Like jerseyshore said, this is a 2-for-1 strategy that can take care of both the deck and existing joists. Looking at the photos in your other thread, I do think 2-piece retrofit OWSJ would be pretty feasible to install in that crawlspace. I'm doing the same thing right now on a crawlspace repair project with joists that corroded away to dust.

 

[KootK]

I'm partial to the new, midspan support if that's spatially viable. But, then, I'm also partial to that kick-ass detail of mine from the past.

Some things that I like about midspan support:

1) Should massively improve the chord stresses.

2) For many older joist types, the webs and their welds are the same full length so you can pretty easily justify them all being okay in many cases.

3) Webs are pretty easy to reinforce.

4) Can localize foundation work to just new, interior foundations for the most part.

5) Avoids some of the hassle of putting in new framing between the existing joists:

a) Jacking the existing joists to ensure even load distribution. Or doing the math to justify not jacking.

b) Installing two piece members with midspan field splices.

c) Dreaming up some reasonable way to fasten any new framing to the underside of an existing deck.

I'm fine with support at the bottom chord too but, then, one must consider:

a) Baked in stresses / jacking etc which can make evaluation a bit tricky. That, or you cut the top chords to make the joists pin ended which is also a bit tricky.

b) If you retain continuity over the interior beam line, you'll probably need a new line of bridging or two on either side of the beam.

With any form of interior support, you'll ideally want to position that intelligently such that you don't create a stress reversal in every single web.