# Strength of Bolt Joints

Bolt joints are formed by drilling holes in the connected elements, inserting the screws, putting on washers and tightening the nuts (Fig. 6.86). The pressure caused by the tightening generates friction between connectors, which decreases or increases along with the changes of equivalent moisture of wood or moisture of wood-based materials.

Minimal spacing and distances between bolts are specified in the norm PN-B-03150:2000 (Table 6.8).

Pressure strength of a bolt joint with wooden connectors can be calculated using the equation (PN-B-03150:2000):

 Fig. 6.86 Example of a bolt joint: 1 bolt head, 2, 4 washer, 3 nut
 Distance signature Orientation Minimal distances of connectors a1 | to fibres (4 + 3|о^а|^ a2 ± to fibres 4d a3t -90° < а < 90° 7d min 80 mm a3c 150° < а < 210° 4d 90° < а < 150° (1 + 6|sinа|)d min 4d 210° < а < 2700° (1 + 6^та|^ min 4d a4t 0° < а < 180° (2 + 2^та|^ min 3d a4c Other values of the angle а 3d
 Table 6.8 Minimal spacing and distances between bolts according to PN-B-03150:2000

where

fh,0,k = 0.082(1 – 0.01dq),

k90 = 1.35 + 0.015d for coniferous wood species, k90 = 0.90 + 0.015d for deciduous wood species, d diameter of bolt core,

pk density of wood.