Shear plates are pieces of hardware unique to wood construction. Local stresses in wood are usually the limiting factor for how much force a bolt can resist. A shear plate grips a larger area of wood around a bolt, to distribute the stresses in wood, and give the bolted connection a higher overall capacity. A recess is cut into the wood face around the bolt hole, allowing the shear plate to be installed flush to the wood surface.
Increasing capacity is the advantage, but there are disadvantages. Any cuts or holes in wood weaken the overall member (reduce the uncut, "net section"), so the shear plate reduces the net section more than a bolt alone. Shear plates almost always need to be shop installed, because they require a special cutting tool and their installation is difficult to inspect as they are usually hidden behind steel side plates in the the finished structure. Shear plate reinforced holes also allow for less installation tolerance. There are three shear plate sizes:
2⅝" diameter shear plates for ¾" bolts
4" diameter shear plates for ¾" bolts
4" diameter shear plates for ⅞" bolts
*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.