fastener design question

[tpmanzi]

I have a 10x8 timber that I want to add 3 - 2x10s to the bottom side of. I need more section for bending. the question is how do I design the fasteners and thier spacing?

 

[drawoh]

tpmanzi,

You need to provide a drawing, and/or ask a more specific question. Your question is way too vague.

JHG

 

[tpmanzi]

more info attached

 

[ishvaaag]

You may do it by a classical approach. Determine the maximum (horizontal) shear at the interface between your pieces, that typically would be in the top interface at the supports. From a shearing stress got this way, choose a separation, multiply by the width and you have the force your fasteners of whichever the type need to stand. These fasteners you need to design in accord with some code (safety factors etc). If the fasteners have some anular clearance may prove inefficent if not compressing the interfaces. So, it is common for these setups to glue the interfaces (it won't be difficult to find an adhesive able to stand the shearing stress) and if so wanted to backup with mechanical means. However a mechanical screws or other mechanical fasteners only approach is also feasible if properly designed; it would be also acceptable to use only adhesive if the code so permits.

 

[diarmud]

Not much help but somewhere I'm sure this is addressed in the National Design Standards, 2005. I'll try to find it tomorrow.