Bearing Design

Using O86 6.5.6.2 for sawn lumber, 7.5.9.2 for glulam, 8.4.7.2 for CLT, and 15.3.3.7.2 for SCL, SIzer determines bearing resistance at the support, for both supporting member and the supports, with an equation of the form

Q_r = f F_cp AK_ZcpK_B

• f = 0.8
• F_cp is the specified strength f_cp multiplied by treatment and load duration factors.
• A is the bearing area, i.e. the area of contact between the support and the member.
• K_Zcp is a size factor defined differently for each material.
• K_B is a bearing length factor defined in 6.5.6.5, which increases the bearing resistance. The factor is not applied if any part of the bearing area is within 75 mm of the end of the member, so that there is check box that can be checked for each support to indicate this condition. The factor is not applied in areas of high bending stress, so that there is a setting indicating the bending design ratio under which it is applied.

A second bearing check from 6.5.6.3 and equivalent clauses following the principal bearing clause for glulam, CLT, and SCL, is required for resistance to the effect only of point loads within a distance d of the support, where d is member depth:

Q_r = 2/3 f F_cp A_BK_ZcpK_B

A_B is the average bearing area of the member transferring the point load and the support, but is limited to no more than 1.5 times the smaller of these areas.

Sizer issues a note under the Bearing Design output table indicating if the point load bearing check governed design.

The bearing equations with Q_r set to the applied reaction force are used to establish a minimum required bearing length to determine the design span, and to determine the design bearing length when you set the input bearing length to unknown.

If a bearing length is established, Qr is compared to the reaction force at the support to determine a bearing design ratio, which is shown in the Bearing and Reactions table of the Design Check output for each support.

For I-joists, only the supporting member is checked for bearing design, Sizer does not design for I-joist bearing resistance.

For sloped members, Sizer implements the compressive resistance at an angle to the grain from CSA O86 6.5.7, which applies to all materials.