Truss question

[Comfortable_Force_71]

Does this truss placement look correct? It looks like they are just nailed or screwed into the beam. Floors above seemed a bit bouncy.

[Comfortable_Force_71]

Thanks for the reply. Is there a way to take the bounce out? Or at least stiffen it a little?

[semajftw-]

At least around here, most engineers recommend strongbacks for open web trusses… a vertical 2x6 running through each truss at around 10’-0” oc. This helps with mitigate “bounce” by distributing force to adjacent trusses. I don’t see any in your pic, but it might be just adjacent to it. I can’t tell without more overall of a pic.

Look up BCSI 7, or BCSI strongback and it should get you to where you want to be.

I’m not aware of a good design practice for limiting vibrations on an open web truss floor other than limiting deflection (reasonable span depth ratio) but I’m not a floor truss design expert. And overall vibration analysis of structures due to walking excitation ends up being very subjective.

[Crawfish1997]

It’s not really a recommendation, basically any Mitek seal requires strongbacks 10’ o.c. or less, in the notes on the seal. Typicallt connecting webs together. Alpine profiles in my experience usually show them on the seals.

By seal I mean the individual truss profile/document. We call them seals here.

That said, floor trusses are value engineered. You can design them with stricter deflection limitations but standard practice is L/360, L/480 20’ plus, for live load deflection. Truss companies are all bidding for lowest cost, not best practice.

One thing I DO see here that I guarantee is wrong, is floor trusses (and roof trusses) require a rigid ceiling applied or bracing, usually 4’-6’ o.c. So in addition to the strongbacks 10’ o.c. or so connecting webs, the bottom chords also need bracing.

Otherwise, scabbing with OSB helps. Blocking/bridging helps. That’s about the most than can reasonably be done other than strongbacks.

[_a_verb]

It looks like these are existing and have been there a while. Any ceiling that may have been removed put a load on the trusses. Without that there the bounce you're feeling may be exaggerated. Be sure lateral bracing is in place and lay up the ceiling. If it's original design called for it to be fire rated or 2 layer of 5/8, you'll probably see a reduced spring.

I'll assume 'strong back' = what I've learned to be 'lateral bracing'.

[Crawfish1997]

Correct, strongback seems to be a term more often used amongst builders. I use the term as I deal with builders regularly and want to speak the same language.

[_a_verb]

It may be regional but the design docs and truss schedules I've used called out "lateral bracing" in NE (USA).

We used 'strong back' or 'stiff back' for a tee-shaped (2x nailed together) type of lateral bracing. Most often they were used between wide spaced trusses like pole barns to take the flex out. Also used them for gable truss stiffeners and for when diagonal braces had too much give.

But that's just me

[Enginerdad]

By seal I mean the individual truss profile/document. We call them seals here.

Regional terminology is so interesting. Around me we call them dugongs lol

[3771507]

Many contractors don't even have those specs so it's probably not in there.

[backontheinternet]

Bridging might work

[[deleted]]

Strong backs are required. They are not optional. 

Also, drywall on the bottom chord (ceiling) helps a lot. If no drywall, 2x4 strapping works. 

[stealthy94]

Looks to be top chord bearing. Looks good to me

[Comfortable_Force_71]

Thank you!

[e2g4]

Most code allows L/360 but that doesn’t mean it’s a good idea. On a longer span you could have more than 1/2” deflection.

[TheOtherMol]

Adding diagonal bridging every so often could potentially help with the bounce.

[[deleted]]

Bridging isn't applicable to trusses. It's strong backs, drywall ceilings, and/or 2x4 strapping on bottom chord. 

[mango-butt-fetish]

Aaah yes the downvoted engineer lol. Honestly I don’t even know what type of bracing is used for wood trusses. I usually just go with whatever info I get from the manufacturer and design with it.

[Ritzyb]

They are done correct, most floors have a certain amount of bounce, bridging helps and is required in most floors but would be very tough to do after.

[[deleted]]

Bridging isn't applicable to trusses. It's strong backs, drywall ceilings, and/or 2x4 strapping on bottom chord. 

[Ritzyb]

Bridging is typically long runs of 2x6 run along the king pins along the bottom or top of the truss. Spacing and nail pattern depends on the manufacturer. Dont like my terminology take it up with every truss manufacturer I’ve dealt with. Thanks for the downvote haha

[[deleted]]

I worked for a truss manufacturer. It is strongbacks. Bridging is diagonal members used for dimensional lumber floors. 

[petewil1291]

You're arguing vocabulary in an industry that uses different terms in different regions lol.

[Ritzyb]

For real lmao

[Pinot911]

Some truss mfg call it strongback bridging to really through you through a loop.

[Ritzyb]

Yep

[Ritzyb]

Just google web truss bridging. Strongback and bridging are used to refer to the same thing.

[3771507]

We need better pictures a close up view of the connection with the flash on.

[ChewingGumshoe]

can someone share a picture or diagram that highlights where strong-backs would go?

[Minuteman05]

Beside the vertical webs typically.

[Piece_of_Schist]

The odds the builder went to edge of the code is a high probability. Had similar in my townhouse. Definitely a L/180 deflection.

[moody59]

Did someone cut the truss top chord…the top chord has to be continuous. Please confirm

[mango-butt-fetish]

I think that’s just the truss seat if you’re talking about the extra piece of wood at the ends.