Wood Beam Moment connection

[Calc1]

The owner wants to add a cantilever balcony to an existing wall, I consider using nails or bolts subject to eccentric shear method as mostly used in steel, but the bolt size ends up too big for the wood member, Anyone has any sujestions? (L Cantilier=4' and Pu=1300 lbs)

 

[jike]

A couple of ideas:

If this is a wood framed building, can you extend the framing back into the building and lap the existing joists?

How about adding a diagonal brace under the cantilever?

 

[Calc1]

Thanks jike
No I can not do diagonal brace under the cantilever, but yes, I can extend it into the existing 2x10 joist but how would you find out how many nails or bolt you need to do the splice, I found out that the fisrt bolt will be 1 1/2 inch, I am not sure, if I am using the right method ( the same way as we do in steel structure, eccentric shear), any suggestion for splice and analysis?

 

[dik]

Can you use metal side plates and glulam rivets? or plywood side plates and adhesive?

Dik

 

[jike]

Normally, the cantilevered balcony joists extend back into the building at least twice the cantilevered distance or more.

Do you really need such a large bolt at the outside wall? Isn't the joists sitting on a bearing wall at the outside wall? Wouldn't the balcony joists also bear at the same location?

The forces at the connections can be figured like a simple beam supported at two locations with a cantilevered end. Extend the lap farther, if you need to reduce the connection forces.

 

[Calc1]

The bolt will be needed for the connection to the existing joist in order to have moment connection and not the wall,

I will be appreciated if you give me any ref. for this case or showing how the side plate and rivets are used in moment connection?

 

[Calc1]

Thank you all,
APA has some info. under "APA Performance Rated I-Joists" on this subject,and the follwing web site

http://www.euken.net/group/seaint/mailarchive/2003b/msg00659.html

 

[FFIELD]

The first thing you learn when working with wood is that you do NOT make moment connections in wood. It is impracticale to do so. Have you ever seen one?

 

[dik]

FFIELD:
Yes... just recently a 30' span gambrel style roof where the owner wanted to use the space... without cross ties...

Dik

 

[archeng59]

it is my experience, that to transfer the moment and shear at the end of the cantilevered wood beam, the quantity/size/spacing of the bolts is typically greater than the member size needed to resist the moments. you need to satisfy the criteria in chapters 7 and 8 of the NDS. it can be done, but it's tough. you will need to work with the owner and architect (if there is one) to get the aesthetics and structural requirements to work out. most times, the owner and architect has allowed the use of a diagonal brace after I've explained what I need to do to get the cantilever to work and meet code.

 

[SacreBleu]

Moment connections in wood are not a good idea - especially when most of the stress is due to dead load. The wood eventually cracks at the bolt holes. Wood is unreliable, in this sense, as opposed to reinforced concrete or steel.

 

[apsix]

I agree this case is not appropriate for a moment connection, but moment connections in timber portal frames are perfectly acceptable. These would typically use plywood gussets nailed to the columns and rafters. Bolts are unlikely to be used due to excessive joint slip for one.

 

[prblmfxr]

I would lap the new balcony joists with the existing joists a reasonable distance (say 2' lap to every 1' cantilever). then design the lap connection for the moment using a force couple (one force near the bearing wall and one force near the end of the lap). Then provide nominal nailing or bolting pattern on the lap between these two designed connections. (Belt and suspenders approach)

 

[Calc1]

Thanks prblmfxr, I can lap 2 times the cantilever, If I understand it then the connection at the wall and the end is only for shear and the nails are sized based on the shear force at the bearing wall and at the end, is this correct?, I do not know how you would find the force or the couple, unless you assume the final beam as one beam and find the moment in that beam and based on this moment, find end forces, use this force to design nails.