Washers: Wednesday's Word Of The Week

Another basic type of hardware that most people are familiar with is the washer. Washers are used in glulam construction whenever a bolt head or nut would bear directly against the wood surface. They protect the finished wood surface from bolt head scratches and crushing.

The most common type of washer used is a "standard cut washer." For a ¾"ø bolt, standard cut washers are 2" outside diameter (O.D.). This is sufficient when bolts are loaded in shear or lightly loaded in tension, the majority of conditions.

If a bolt or rod is highly loaded in tension, crushing of wood under the 2"ø washer will control design, so larger washers are available to increase capacity. The simplest are New York Dock Department (NYDD) washers, which are simply 3" O.D. washers cut from ¼" steel plate. Malleable iron washers are also 3" O.D. with a shaped profile that is ½" thick overall - they are very strong with good corrosion resistance. Either of these will increase area (and therefore total compression capacity) of wood under the washer by about 2.5 times. 

*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.