ABSTRACT
This chapter focuses on the transition to wooden trusses with built-in adjustments for wood shrinkage. It is difficult to ascertain the degree of scientific understanding that early builders had about the stresses present in roof trusses. Early builders seemed to know that an all mortise-and-tenon truss would be limited in its span without a failure at the joint between the post and the bottom chord. An additional purpose is to attempt to "date" the switch from the traditional use of mortise-and-tenon joints and iron U-straps to the more structurally efficient use of machine-made bolts for structural connections. It must be remembered that the simpler mortise-and-tenon trusses continued to be built until well after the introduction of bolted connections, but the transition of technologies could serve as something of a benchmark date. The shrinkage of wood causes internal stresses, twisting and checking, especially at those joints that were secured with mortise-and-tenon joints.
