Wood Truss Connections


The above wood trusses were just delivered to the job site.   Let's take a look at the member connections.



Are the connections glued?



No.  The members are connected by metal "gang nailed" gusset plates - one on each side. 



If glued and in tension, the horizontal member could pull the face grain off of the vertical member.


Ok.  What about model building? 


There is a member missing.  It pulled off the face grain of the long member.  We used a pencil to shade the face grain that remained. 


So,  what to do about this problem?

The picture above also shows a member that was not pulled off.  Its connection has hat buckram wrapped around it.


Hat buckram wrapped around a connection.


Hat buckram is a fabric used to make ladies wedding hats.


We cut strips of hat buckram, dip them in glue, and wrap the glue soaked strip around the connection.  If you can keep the connection from failing, the strength of the structure can become a function of the individual member strengths.  Of course there are other failure modes such as a lateral buckling of the structure as a whole due to inadequate lateral support.

Note:  Hat buckram is stiffer in the non-wavy direction.  Cut the strips so that the straight fibers are parallel to the long direction.


What if the competition rules do not allow the use of hat buckram?

You might try cutting strips of wood for gussets.  

Watch out!  The orientation of the gusset grain is important.  Wood is weak in tension perpendicular to grain.