Stacking Wood Posts

[bookowski]

See attached sketch.

I have existing floor joists that have had an interior bearing wall removed. The joists do not work (by calc) without this wall. We are installing dropped headers below the existing joists where the wall was removed. The posts at each end of the headers will not align with existing joists (see sketch). Any suggestions for a good detail for stacking these posts, 3 stories with the same condition on each.

 

[dhengr]

Bookowski:
You better be using double extra strong sub-flooring on that detail. You could just put a vert. stub of the same post mat’l (as blocking). in joist depth to transfer the column loads, but that rests atop a beam, and the beam’s compression perpendicular to the grain will control the cap’y. of the detail. Now multiply that by three, and include the cross grain shrinkage and crushing at each level. You haven’t given any loads, span lengths, tentative sizes, etc., so it’s tough to say. Maybe frame the beams into the side of the columns/posts with some sort of hanger and an added cripple stud/studs under each beam end. Then cut a hole in the sub-floor and run the posts end to end, good square end cuts and fit, with some side plates to tie them together. Now compression parallel to the grain controls the design and layers of differential shrinkage go away.

Pay attention the how you sequence this construction and you can probably save yourself some work, lugging temp. mat’ls. and temporary shoring and bracing operations. Design from the top down to size everything and design the details. But, build from the bottom up and the lower levels will likely support what’s going on above. You must check this out. Obviously, at each level you must temp. support the fl. joists above as you remove the existing brg. wall and insert the new beam and columns. But, you probably don’t have to brace all levels for the full duration. The tenants will love you. Of course, move any grand pianos away from the work area.

 

[msquared48]

Three things:

1. Add solid blocking between the bottom of the column and the new beam at each level, the full width of the column. Depending on the load of the column and the bearing area of the column, you may need to add steel bearing plates to avoid crushing of the blocking, or a larger area column to limit the bearing stress.

2. Provide blocking at all interstitial spaces between the joists over the new beam.

3. I would recommend doubling up at least the first floor joist beyond the end of the new beam, if not the first tgwo or three. for differential deflection reasons.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[bookowski]

dh: I didn't provide spans/loads because sometimes it takes things off track with other questions. The joist span (into page on sketch) is about 20', the header span will be about 12'. There are two residential floors (single family) and a roof. The walls were already removed so the joists are spanning the full 20 now but essentially have no load on them (walls were removed by demo prior to my involvement). This is an old place and the joists are very undersized which is typical for the type of house. In fact at the roof some of the joists were turned flat at the rear for headroom.

I was thinking of similar details to what you said. I looked at simpson header hangers to go off the side of the post but the loads are too large and I don't like the eccentricity. I also thought about the cripple stud idea but it gets weird with stacking. I think I may just have to block solid and oversize everything to satisfy crushing. I don't feel comfortable adding a stub of post, it seems unstable.

msquared: There is actually a wall beyond the post, I just didn't show it because it's not an issue. So there shouldn't be a diff. deflection issue there.

Thanks for your inputs.

 

[amecENG]

How about something like this: