Trusses supported on face of beam 1

[JStructsteel]

See attached detail.

New building up against existing building, going to be opening up the wall and supporting the existing trusses from a new beam. Going to face hang them to maximize ceiling height. What do you think about the bracing of the new beam, it will be supported on a new 2x wall, but on top of the top plate. Was going to brace it back to the existing roof, that then is over-framed

Any issues you see?

 

[Ron]

A couple of comments:

1. How are you attaching the Parallam to the top plate?
2. You are bracing the parallam to the same item that is hanging from it. That would have little or no lateral resistance. Brace to the new trusses, not the old.
3. How are you preventing a "hinge effect" at the bottom of the parallam other than the top bracing?
4. If you add one more layer to your top plate, reduce the depth of the parallam and overlap the Simpson hanger between the parallam and the top plate you would prevent any hinge effect and engage lateral resistance at the wall.

 

[XR250]

I do not see any issues with this. I use a similar detail. Maybe add a strap at every other truss from the bottom chord wrapped up around the non-hanger side of the beam to help resist the tension portion of the couple as hangers are not really designed for tension loads.

 

[JAE]

Just my own preference - you should go much farther in specifying the 2x4 braces.
Spacing, connection, nailing, etc.
The brace's connection to the truss may not align with a truss panel point. Is that OK for the truss?

Also - I would typically add a note that the contractor must temporarily support the existing trusses at panel points and provide adequate between-truss lateral bracing in line with the shoring to allow cutting of the trusses and installation of the new beam.
I would also check that the trusses can resist the newly applied end moment from the beam-to-connection eccentricity. Probably OK as bracing force isn't always that great but you should at least verify that.



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[slickdeals]

Agree with Ron. You need to prevent the "twist/rotation" at the ends of the Parallam. Attaching to the new truss is perhaps the way to go.

 

[KootK]

I see no issue with this mechanically. The bottom of the beam is restrained laterally by it's connection to the truss heels. The top of the beam is restrained laterally by it's connection to the truss top chord. Check. It bothers me not at all that the beam and trusses will flex/rotate together.

All that said, I think that it will just be easier and cleaner to get your bracing out of a new truss. I'd do this:

1) Slide the nearest new truss up snug with the beam.

2) Ask the snug truss to be a "structural gable end". In truss lingo, this means there'll be a crap load of verticals plated in among the structural webs at 2' oc or whatever you say.

3) Add some 2X strong backs to the vertical webs for convincing stiffness etc.

Come to think of it, why not just replace the beam with a truss girder?

 

[KootK]

I could even get behind this. In a way, you'd almost have this same mechanism if you did nothing at all. The hangers have some tension capacity and the beam is going to LTB to the right owing to the inherent torsion.

 

[JStructsteel]

Ron (Structural)
10 Mar 19 18:31
A couple of comments:

1. How are you attaching the Parallam to the top plate?
2. You are bracing the parallam to the same item that is hanging from it. That would have little or no lateral resistance. Brace to the new trusses, not the old.
3. How are you preventing a "hinge effect" at the bottom of the parallam other than the top bracing?
4. If you add one more layer to your top plate, reduce the depth of the parallam and overlap the Simpson hanger between the parallam and the top plate you would prevent any hinge effect and engage lateral resistance at the wall.

1. Simpson EPC42
2. Im thinking the cut truss braces the beam pretty good from rotation, just want something at the top. The load is going back into the existing roof diaphragm, and dispersed
3. The existing trusses brace the beam, and its also fastened with the simpson connector
4. The hangers are at the opening, there is no top plate there to fasten to.

 

[JStructsteel]

I see no issue with this mechanically. The bottom of the beam is restrained laterally by it's connection to the truss heels. The top of the beam is restrained laterally by it's connection to the truss top chord. Check. It bothers me not at all that the beam and trusses will flex/rotate together.

All that said, I think that it will just be easier and cleaner to get your bracing out of a new truss. I'd do this:

1) Slide the nearest new truss up snug with the beam.

2) Ask the snug truss to be a "structural gable end". In truss lingo, this means there'll be a crap load of verticals plated in among the structural webs at 2' oc or whatever you say.

3) Add some 2X strong backs to the vertical webs for convincing stiffness etc.

Come to think of it, why not just replace the beam with a truss girder?

1. The trusses span 44+/- across the building. This opening is only about 17'-0"

Was going to use a girder truss, but the truss folks were going to use a 4 ply truss. Huge for whats needed.

Here is a side view of the detail

 

[txeng91]

Couple comments

-Assuming you have net uplift at the beam bearing, strap the face of the beam down to the stud pack below and put a holdown in at the base. Post cap might not really work if you have a double top plate. Also check the 2x4 stud pack, might be overloaded if the plate height is high

-There might be a couple thousand pounds of in plane lateral force to transfer from the beam to the wall for diaphragm chord or strut action. Can you extend the beam past the stud pack and attach through the bottom of the top plate up through the beam with screws/nails?

-Your section view might be off, usually the bottom of the top chord and the bottom of the bottom chord would meet at the outside corner of the existing wall plate. You have the top chord higher on your drawing.

Side note: You might consider using Koots detail with clip angles both sides to eliminate need for temp shoring. They could install everything before removing the existing wall. U hangers might be better though, just a thought.

 

[JStructsteel]

-Assuming you have net uplift at the beam bearing, strap the face of the beam down to the stud pack below and put a holdown in at the base. Post cap might not really work if you have a double top plate. Also check the 2x4 stud pack, might be overloaded if the plate height is high

-There might be a couple thousand pounds of in plane lateral force to transfer from the beam to the wall for diaphragm chord or strut action. Can you extend the beam past the stud pack and attach through the bottom of the top plate up through the beam with screws/nails?

-Your section view might be off, usually the bottom of the top chord and the bottom of the bottom chord would meet at the outside corner of the existing wall plate. You have the top chord higher on your drawing.

Side note: You might consider using Koots detail with clip angles both sides to eliminate need for temp shoring. They could install everything before removing the existing wall. U hangers might be better though, just a thought.

1. No issues with the capacity of the stud pack, uplift, etc.
2. The existing building shear wall will remain, im only transferring 17' of lateral load thru the new beam.
3. Im not sure what you mean. these trusses are being cut
4. The trusses have to be cut, so they will have to be shored.

Thanks.

 

[txeng91]

2. There’s a good chance that the post cap doesn’t not have enough lateral capacity if you’re on a shearwall line. You have to calculate the drag force and transfer it directly into the top plate.

3. Your showing the bottom face of the top chord flush with the top face of the bottom chord at the exterior face of the wall. Usually the bottom of the top chord is flush with the top plat at edge of the wall. E.g. if you had a 6/12 roof slope with a 2x6 top chord the dimension from the plate height at the edge of the wall to the bottom of the roof deck would be 6 1/8” (5 1/2” at a 26.6 degree angle from horizontal. Your section shows the full depth of the top and bottom chord at the edge of the wall. I could be wrong but that’s just what’s typical.

4. From your sketch and description it sounds like the only modification to the trusses is removing the existing eave overhang, which is just a top chord extension. If the extension is removed and the truss is properly connected to the beam prior to removing the existing wall, shoring shouldn’t be required. That said there may be a construction sequencing issue there, it was just a thought.

 

[msquared48]

The trusses probably have metal plate connectors.

Keep any new truss end tail cuts well clear of the plates - 1 to 2 inches at least.

Mike McCann, PE, SE (WA)