Bolted joints in timber

A bolted joint connects two or more timber members by bolts passing through holes bored in the members, with a washer under the head and the nut; the bolts transfer the load by bearing on the timber and by their own bending.

• Types: lap joints and splices with timber or steel side plates, and tension or compression splices; the bolts act in single or double shear.
• Load per bolt depends on the bolt diameter, the thickness of the members, the species and the angle of the load to the grain (it is higher parallel to the grain than perpendicular to it).
• Spacing rules (IS 883, typical): holes $1$ to $1.5$ mm larger than the bolt; spacing of bolts in a row along the grain at least 4 diameters; end distance 7 diameters in tension members and 4 diameters in compression members; edge distance at least 1.5 diameters (4 diameters at the loaded edge when the load is perpendicular to the grain); spacing between rows about 2.5 to 5 diameters, depending on the ratio of member thickness to bolt diameter.
• Details: washers prevent crushing of the timber; bolts are tightened again after the timber has seasoned; avoid bolts of very large diameter in thin members.