timber construction - connection details

[n3jc]

Hi, i have another question.

I attached a picture with a problem.
force in support A is to big for connection with only one steel bolt. So I made wood support nailed to column. is this OK? i have a feeling its not, because there will be some small rotation around that support and vertical force wont apply to the center of this nailed support... What do you think? Any suggestions? In other supports like B,C and D a force is not that large so its not a problem - one steel bolt is OK.

 

[KootK]

I think that you're fine. In my experience, most engineers would not worry about the rotation in a situation like this. It's not as though we would if the beam were bearing on a post. And really, a nail group is going to be pretty ductile and able to adapt. I might provide 25% more capacity just to be safe. Another issue that might warrant consideration is load sharing between the bolt and the nailed connection. You're probably going to need the nail group to displace a fair bit before you really engage the bolt. Could you design the nailed connection for the total load? Alternately, can you use multiple bolts and eliminate the nailed connection?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[n3jc]

Tnx for reply... nailed connection is designed to take the total vertical load. Steel bolt is there only for horizontal connection/stability...

If I choose 2 or 4 steel bolts in detail A instead of nailed wood support - isnt there a problem with moment? I think i should design steel bolts in this case to vertical load + shear forces because of moment? in case of more then one bolt - what about forces from a moment applied to a column? that might be a problem? or it isnt because its timber and its ductile so there will be rotation/deformation in joint.

 

[dik]

Can you use a 'split ring' shear connector and just the bolt(s)?

Dik

 

[KootK]

If I choose 2 or 4 steel bolts in detail A instead of nailed wood support - isnt there a problem with moment?

Same answer. I see your point but I, and I believe most other engineers, would not sweat the moment transfer into the column. Obviously, the stiffer your beam is, the less of a problem it's going to be. Also, creep in the connection is going to tend to dissipate your joint moment. Kinda like concrete columns.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Split ring connectors are great, but there's very few contractors that actually have the knowledge and tools to install them.

I'm with Koot. All nails or all bolts. Wood is fairly flexible so I wouldn't worry about the moment transfer too much

 

[dik]

It's been a year or so since I used split rings, but they are easy to install and almost a no brainer and they substantially increase the load transfer capacity... and 'all nails or bolts' works for me... The contractor, however, has to know how to use a drill and possibly a hammer.

Dik

 

[jayrod12]

They always get kicked back when I've tried specifying them. And we work in the same area. So it may be the contractors you work with are comfortable with them. But the majority are not. At least in my experience.

 

[molibden]

Nejc, connection B does not pass with just one bolt M16 at 31,6 kN shear force. You have softwood specified C35 (not common) and hardwood D50 (also not common in roofed construction).

Detail A is generally OK but if the wood dries then the whole force will apply to the bolt and beams tend to crack/split.

Don't worry about moments because you don't have a moment connection. You have a shear connection, moment is taken by the beam itself. Rotation is minimal - negligible.

With such forces I would use more bolts OR self tapping screws at an 45 deg. angle.

 

[n3jc]

@molibden ... you are right. M16 is OK for C and D detail but not for B - there are two shear plane so 31,6/2 = 15,80 kN ... M22 (10.9) is OK.
About wood class C35 and D50 - i know its not common but i couldnt get through with clasic C24. i had limitations about dimensions. I hope its OK.

 

[molibden]

Class C35 is hard to get certified. In these dimensions I would specify glued laminated columns. Also you get it with certified strength.

 

[n3jc]

What about other classes like C40 and D50? I dont know why there are so many classes when in reality class C24 and C30 are almost always used... u cant be wrong to select other clasess, can you?
In my country engineers use C24, C30 and sometimes C35. but when it comes to construction, contractors dont give much damn about it as far as I know. there are also big safety factor for material gamaM = 1,30 and Kmod= 0,9 or less, that brings cca 70% of characteristic value.

 

[n3jc]

@molibden wrote: Don't worry about moments because you don't have a moment connection. You have a shear connection, moment is taken by the beam itself. Rotation is minimal - negligible.

So if I change detail A to 2 bolts instead of nailed support i dont have to worry about shear horizontal forces transfered into wood column? If thats the case the only thing i need to do is to control shear capacity of two steel bolts and thats it? Same thing would apply if i use 4 bolts? im adding a picture.

hope you ll answer. tnx.

 

[molibden]

Well, you should know if they can build it as intended. I never use more than C24 for solid wood. Maybe C30 if we discuss it upfront and engineered wood will be used.
GL you can get up to GL36 no problem. Hardwood I don't know. Probably nobody grades solid hardwood. Visually yes, but with numbers no. Better to presume lower characteristics in the beggining.

 

[molibden]

In this case yes, that's the whole story. In some other case, you would need to account for additonal forces. Dont forget other checks as well (netto cross section, effective number of bolts parallel to grain, splitting resistance of beams, edge distances..).

Couldn't you notch the column a bit to interlock with beams? It would certainly be a stiffer connection.

I still can't imagine different wood species for beams and columns.

Good luck

 

[Leftwow]

Ah I thought you had to provide a bearing surface for the connection in vertical loading... interesting.