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Rafter Thrust

That looks like any of a hundred frame jobs I have seen...and failed back in the day. Lots of engineering solutions have been come up with after the fact, many some variation of the strap steveray shows. I encountered this very heavily in the rural south, and saw more than a few failures where the exterior walls were blowing out. Very common in "bonus room" framing which is usually made worse by using knee walls at the exterior. Once demonstrated the issue to a builder (on a very nice home) by having him help me measure across the room at the bottom and the top plate. I asked him if he purposely installed the knee walls several inches out of plumb. This was made very apparent by the "temporary" t-posts they were using to hold up the ridge board. It was bowed so badly the nails were bending at the connection.

In Jar's photo a flat strap across the bottom would do it, but might ruin the finish product. Also, I rarely have seen ledger framing outside of the south, which makes a nice finish, but the ledger nails look a little far apart.
 
I don’t see the problem. Looks like 3 toe nails from the joist, part way into the beam web … we always do it that way …
 
So this is what they are trying to rercreate:

1692625904666.png

3-16d is about 360# in shear if I remember....So lets call it 400# these are not giant forces we are dealing with....The flat strap under is a problem for the drywaller ...
 
Sorry...mis-clip.....at 30# load and a 7 pitch or steeper, it's about the same (what's a 16d or 2 amongst friends..Not that anyone builds with 16ds anyway, so it probably has 10 10ds....And kind of moot as once again...It's all trusses per the energy code around here now...

1692630446221.png
 

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steveray said:
I recommend a Simpson VB-7...but it is way overkill, but you can point to it in the book, so it is easy.......You are looking at controlling about 400# if you are using the prescriptive nail connection...

View attachment 11170
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www.strongtie.com

VB

The VB provides lateral resistance force at the bottom of beams when installed approximately 45° or more to the vertical plane.
www.strongtie.com www.strongtie.com

Screenshot 2023-08-21 at 10-23-08 C_VB10_2DP_Cad_ISO_Instld.dwg - C_VB10_2DP_Cad_ISO_Instld.pdf.png
Never seen this used. Usually see CS-22. Almost always specified by an engineer. The dry-waller can work around it.
 
e hilton said:
I don’t see the problem. Looks like 3 toe nails from the joist, part way into the beam web … we always do it that way …
Click to expand...
Referring to the ledger nails. I had it in my head that they should be closer, but the current codes don't give a dimension, and the code I thought they exceeded calls it 4" o/c, so these are probably fine. Ledger framing provides a much better finish, produces less squeaks, and is cheaper and quicker. JMHO.
 
Jar, are there any collar or rafter ties above the CJ/Beam connections to prevent spread?
 
Sifu said:
Referring to the ledger nails. I had it in my head that they should be closer, but the current codes don't give a dimension, and the code I thought they exceeded calls it 4" o/c, so these are probably fine. Ledger framing provides a much better finish, produces less squeaks, and is cheaper and quicker. JMHO.
Click to expand...
You mean this?

1692650201938.png
 
steveray said:
You mean this?

View attachment 11183
Click to expand...
Yes. Back in the day in another state with a state code, they prescribed it in this table and I guess I mis-remembered it as "within 3" of the joist, so one nail under and 2 or 3 within 3" of the joist. But, I went back and can only find that it says 4" o/c. It may have come from an earlier edition, or it may be that I have been wrong all along, and current code has no distance prescription anyway with "At each joist".
 
Relative to tension force from inside ends of attic floor joists, at main beam (girder).......... that resist outward thrust force from low ends of rafters;

Angled nails ("toenails").........installed to connect inside end of attic floor joists to side face of main beam........are not resisting force from attic floor joists as shear force in "normal" way considered for NDS provisions governing design shear capacity for toenails.......which is for downward-acting force due to vertical load on joists. Such nails resist tension force from floor joists mostly in withdrawal (from main beam).......and are susceptible to weakening over time with cycles of snow load on roof. For relatively small outward thrust force........such connections can work...........however, for larger houses and lower-slope roof, such connections are not adequate.

If top of beam is flush with top of floor joists, then most effective method for resisting outward thrust force from low ends of rafters is to install plywood floor sheathing......even if only 4-feet wide.........securely nailed to attic floor joists on each side of beam.

Other method that should be considered ........if main beam is available...........is to design beam to support ridge member (of roof) along with attic floor load.
Snow load and floor live load can be reduced when both design loads are combined for same load case.

Simpson connector shown in previous post surely can work...........though not really required for every joist if plywood can be installed on floor joists on each side of beam. Install strip of plywood (4-feet wide is best) on each side of beam, securely nailed to joists with 8d nails at 6-inches or less. Narrow open-strip can be provided adjacent to each side of beam to provide clear access for installation of connectors (to joist and beam)..........which could likely be spaced at every third joist or even more, depending on allowable tension capacity and required thrust force. Plywood will essentially span between connectors as deep horizontal beam.......or "diaphragm".
Other connectors can be used with same approach.
 
To clarify comment in previous post about strap connectors being spaced at "every third joist or more";
Spacing may be governed by shear capacity of nails in plywood. If entire attic floor were to have plywood floor sheathing..... then design capacity of connector would govern spacing. However, if only 4-feet wide strip of plywood is provided on each side of beam..........then spacing of connectors will likely be governed by shear capacity of nails connecting plywood to floor joists that have connectors.
Spacing at every third joist could be used for moderate thrust force conditions. However, for relatively large thrust force conditions, spacing of connectors would have to be at every second joist or even at every joist...........unless more plywood were installed.
 
Relative to tension force from inside ends of attic floor joists, at main beam (girder).......... that resist outward thrust force from low ends of rafters;

Angled nails ("toenails").........installed to connect inside end of attic floor joists to side face of main beam........are not resisting force from attic floor joists as shear force in "normal" way considered for NDS provisions governing design shear capacity for toenails.......which is for downward-acting force due to vertical load on joists. Such nails resist tension force from floor joists mostly in withdrawal (from main beam).......and are susceptible to weakening over time with cycles of snow load on roof. For relatively small outward thrust force........such connections can work...........however, for larger houses and lower-slope roof, such connections are not adequate.

If top of beam is flush with top of floor joists, then most effective method for resisting outward thrust force from low ends of rafters is to install plywood floor sheathing......even if only 4-feet wide.........securely nailed to attic floor joists on each side of beam.

Other method that should be considered ........if main beam is available...........is to design beam to support ridge member (of roof) along with attic floor load.
Snow load and floor live load can be reduced when both design loads are combined for same load case.

Simpson connector shown in previous post surely can work...........though not really required for every joist if plywood can be installed on floor joists on each side of beam. Install strip of plywood (4-feet wide is best) on each side of beam, securely nailed to joists with 8d nails at 6-inches or less. Narrow open-strip can be provided adjacent to each side of beam to provide clear access for installation of connectors (to joist and beam)..........which could likely be spaced at every third joist or even more, depending on allowable tension capacity and required thrust force. Plywood will essentially span between connectors as deep horizontal beam.......or "diaphragm".
Other connectors can be used with same approach.
Click to expand...

I didn't understand anything you wrote. Something abut attic floor joists? How did you get from that to ridge beams?

Please explain you question better.
 
Yankee Chronicler said:
I didn't understand anything you wrote. Something abut attic floor joists? How did you get from that to ridge beams?

Please explain you question better.
Click to expand...
Responding to issues in thread...........not asking question.
Attic floor joists generally used as rafter ties to resist outward thrust force from low ends of rafters...........that is basic condition "setting stage" for issues discussed in this thread.
However...........requirement for transferring tension force in attic floor joists.......across flush-framed attic beam that supports inside ends of attic floor joists..........is resolved if structural ridge beam can be used to support high ends of rafters..........since then there is no outward lateral force at low ends of rafters.
Of course.........ridge beam must have adequate supports.............which, in this case, could be provided by attic beam as long as attic beam has adequate design capacity to support attic floor and ridge beam at same time.
 
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