Thru bolting milled logs 1

[4thorns]

Hi all,
I have literature that provides me with vertical thru bolt spacing for certain spans @ certain loads to make up to 4 milled logs act collectively as one beam. I have the design properties for all the log profiles and rectangular beams. What I don't have is the formula(s) used to determine the spacing of the thru bolts. These bolted logs would, in most cases, be over a large window or french door with roof load above. The logs would also run beyond the ends of the opening up 4' and there would be no butt joints within the span. Any help with determining the required spacing of the vertical thru bolts would be greatly appreciated.

Thanks,
Doug

 

[RockEngineer]

Back to the Basics VQ/I. If you know the loading and the span you can determine the shear flow the bolting needs to resist. Determine the Q based on the intersection between the highest and second log. Your highest shear will probably be near the edges of the opening and if you apply that throughout the entire opening you will be very conservative. Just like when you are nailing a horizontal and vertical board together to make a Tee and need to determine the nailing.

 

[smb4050]

You should be able to find the spacing of the bolts in an Mechanics of Materials book. Mine is Beer, Johnston and it in Chap. 5, Transverse Loading, Sect 5.3, Determinantion of the Shear on a Horizontal Plane.

q = VQ/I where V is the shear, Q is the 1st moment about the neutral axis, I is the moment of inertia of the entire cross-ssection. q is the horizontal shear per unit length, so divide q by the bolt's controlling limit state for shear giving the spacing per bolt.

What about shear deflection?

 

[asixth]

Depends on the beam depth to length ratio. Shear deflections for beams which are deep relative to their span will have a greater contribution of shear deflections to their overall deflections.

Also the method on how the E-modulus of the wood has been established will also be a factor. If the timber has been graded by load tests than a proportion of the shear deflections will be accounted for in the calculation of the E-modulus.

Please refer to a recent thread in the Structural Engineering Other Technical Topics forum for discussion.

thread509-269178

 

[dhengr]

4thorns:
If you calc. q = VQ/I correctly you will have the shear flow in lbs/inch at the given joint btwn. logs; times bolt spacing = shear at the bolt. q will be greatest near the reactions and at the faying surfaces nearest the mid-depth of the beam. Be careful not to read to much into smb4050's statement about the ‘bolt’s controlling limit state’. That is not the single shear strength of a bolt in a steel to steel pl. connection; but rather, look at the NDS’s treatment of single shear bolted connections; that’s called the European yield model theory. Use that as a good guide, but you will have to do some interpolating since your logs may not be stress graded. The bolt actually shearing is not likely the failure method when you look at the EYMT. You could actually use small split-rigns or toothed-rings out near the beam reactions to increase shear cap’y.