Nailed Moment connections in wood

[KeySol]

am tryign to setup a spreadsheet or a matlab program that will "design" scab reiforcement for trusses members. The webs seem straight forward and where i am running into questions is with chords. I am wonderign if 1. there is some guide or reference manual i can use to help guide me through this, if not, then 2. how do i design nailed connections for moment transfer.

I see that in most of the steel design manuals they show how to do an elastic design of groups of bolts for an eccentric load. Since a moment is just an eccentric load i am wondering if it is acceptable to do a similar type of analyis for a nailed connection (most difficult part is to assume and determine where the nails will be located). Any thoughts out there on this?

 

[Ron]

In general, no such thing as a nailed moment connection in wood!

 

[msquared48]

Personally, I would bolt at the thought of being screwed with a nailed moment connection.

By the time you got enough nails into the wood member, the strength would be seriously compromised.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[woodman88]

To scab a member to a truss chord you nail the scab for the plf you need to transfer. If you extend the scab pass the joint enough than you won't need to add clusters of nails at the ends of the scab.

Garth Dreger PE
AZ Phoenix area

 

[MikeHalloran]

I built a (hopefully temporary) end truss to shore up the roof of a house after Andrew. It was connected with nails and scabs because I didn't have anything else.

The connections had a crapload of nails in them and still barely survived erection, jacking up the deflected roof by hammering the truss into the gap.

I don't think a nailed truss is a good idea under any circumstance. I wouldn't have done it at all, except that the owner's wife was getting hysterical about keeping the looters out.



Mike Halloran
Pembroke Pines, FL, USA

 

[MiketheEngineer]

Too many nails too close just pulverizes the wood. While truss plates come about as close as you are ever going to get to making any kind of moment connection - I am not sure if any are rated as such.

When I was in that world - they were not - although some conservative estimates did seem to test out OK. But never really put into practice.

 

[woodman88]

MiketheEngineer- Wood truss plates have always had moment capabilities. The truss heels (where the top and bottom chord meet at a bearing) is the prime example of this.

Garth Dreger PE
AZ Phoenix area

 

[msquared48]

And a couple other thoughts here...:

By using so many nails in a plywood plate, you are inhibiting the ability of the wood members to shrink perpendicular to the grain, and thus encouraging horizantal cracking of the member at the connection, weakening any moment resisting ability as time goes on. To prevent this, the connection would have to be very carefully detailed with this in mind.

Plus, with the use of plywood scab plates, you cannot rely on the full thickhness of the plywood for the nailing values. Not the same as solid lumber or metal side plates.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

Garth -

I agree with you and even worked on quantifying those numbers MANY years ago.

I just have never heard of any really good results - or maybe the truss plate mfgs keep that info to themselves - as I probably would.

 

[HouseBoy]

" In general, no such thing as a nailed moment connection in wood! "

What do you call the APA Narrow Wall Bracing detail?

 

[Ron]

APA Narrow wall bracing takes into account a lot more than a simple, single moment connection.

Read the response...."in general" means in most instances...there are no nailed moment connections in wood.

Can other conditions be designed? Of course...connections can be designed to withstand/transfer moment...but that is rather rare for wood frame construction.