NAILED JOINTS

NAILED JOINTS

Joints connecting structural members are essential to the strength and performance of the building. They are usually the “weakest link”. Until framing anchors came along, nails were about the only way to hook two pieces of wood together cheaply and quickly. Framing anchors usually transfer loads through nails or screws in shear.

Side, toe, and end nailing are still common methods of connection. Nailing is actually a poor way to connect lumber, since it takes many nails to transfer the inherent strength of wood. Moreover, quality control is difficult, and there are many variables than cannot be evaluated. Never-the-less, we still nail because it is fast, economical, and most everyone can swing a hammer.

Nails should be placed in a triangular or staggered pattern. Avoid placing more that one nail into an individual growth ring. Beware of over-nailing. The last nail you place may end up splitting the piece, compromising the joint. Then what will you do?

When connecting temporary braces use a double headed nail; but if using a regular nails, try not to nail flush, instead leave about 1/8 inch proud for ease in withdrawal when dismantling. This has safety implications.

Edge nailing: When connecting members loaded in transverse shear (i.e. beams), be careful to avoid placing nails too close to the edge on the loaded side. Confine your nails to the “lower” 2/3 of the piece.

Toe nail or not toe nail? That is the question. You learned in high-school wood shop that toe nailing is a good thing. Maybe, maybe not. Remember that forces operate in a straight line. A nailed joint transfers loads by shear or withdrawal (tension). Nails driven straight (normal) into a joint provide better withdrawal resistance against normal loads than nails on a slant. Can you draw the force resolution to demonstrate this?

The power nailer is a mixed blessing. It is handy for placing nails without hammering, when hammering will disturb the joint arrangement. It is also faster than hand nailing. But it is dangerous to use, especially in the hands of the novice. Its ease and speed makes it the frequent cause of over-nailing, which can actually weaken joints. For temporary framing of braces, etc. it is a bane, since too many nails often are placed and usually placed too deeply for ease in dismantling.