Bolting Wood Beams Together

When joining pieces of wood together using a carriage bolt the square head on the bolt can become stripped in the hole making them hard to tighten.

Bolting wood beams together. Images courtesy of eurocode 5 for example if two 47mm x 195mm are bolted together then m12 bolts should be used and positioned 48mm from the top and bottom and at least 48mm apart vertically if staggered fixings are used. To solve this problem insert a few finishing nails in the hole beside the bolt before hammering the bolt into place. The nails will fill the gaps between the hole and bolt to keep it from spinning. This course will feature a bolt design example utilizing awc s 2015 national design specification nds for wdc t tiwood construction.

Drill through the beam with a long bit the same diameter as the bolts. Stagger the bolts and make sure the bolts are placed a minimum of 2 1 2 inches from the edge of the beam. Bolts must be closer than seven times the diameter or 80mm from the joist end and four times the diameter from the top and bottom. An example of a regular bolting pattern might be 1 2 inch diameter or 5 8 inch diameter bolts spaced 16 inches on center.

Be on the safe side when in doubt and use extra nails. While code typically allows 3 8 inch diameter bolts for fastening braces to posts beams or joists i use 1 2 inch diameter bolts instead. A 2x10 beam should use a minimum of 4 3 nails fastened in a vertical pattern from both sides of the beam every 16 on center. Starting about 2 inches from the edges of the beam counterbore two holes on the inside or the least visible side of the beam for carriage bolt nuts.

T i ill i l d ti d itopics will include connection design philosophy and behavior an overview of 2015 nds provisions related to bolt design including appendix e for. Connecting wood beams with through bolts is a safe and easy way to secure two wooden support beams together.