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Refer to Bearing design -Beams,and Bearing Design - Columns and walls for a description of the Sizer bearing design for both the main member and the supporting members at each support and at the column base or wall bottom plate. The program designs for the critical bearing of main and supporting member.
Column bearing plates (NDS 3.10.1.3)
This clause states that bearing plates are to be used of the axial bearing response ratio is greater than .75.
Sizer implements this clause via a note under the Analysis vs allowable Stress table in the design results.
Bearing at an angle to the grain (NDS 3.10.3)
The NDS specifies that bearing at an angle to the grain use a combination of resistance values using Hankinson’s formula as follows,
Compressive strength at an angle to the grain:
Where theta is the angle between the grain and the load.
The value Sizer uses is the F’ value as computed above for sloped beams. The theta used will be the complement of the slope angle. The program outputs F’theta in the reactions table under each bearing.
Bearing Area Factor (NDS 3.10.4)
For bearing lengths Lb less than 6”, a bearing factor is permitted to be applied to the compressive resistance Fcp such that
Bearing area factor:
This applies to lumber, timber, glulam and SCL. This is equivalent to adding .375” to the bearing length when it is used to compute the bearing stress on the member, when the bearing length is less than 6”.
When the minimum bearing length calculated as
is less than 6.375”, Sizer will adjust the calculated minimum bearing length as follows:
Minimum factored bearing length:
Therefore, the allowable bearing capacity is
If there is a bearing area factor different from 1 for any support, a line appears in the Maximum Reactions and Bearing Lengths starting with Cb and showing the value under the supports, even if it is 1.
CLT Bearing Factor
For floor and roof panels, bearing length that is the width of whatever is supporting the member, and the corresponding Cb factor.
For the supporting member it means a bearing length that is the one-meter or one-foot design width, which means Cb = 1.0, as it should be for continuous support. .
For wall panels supported by sill plates, the sill plate bearing length is the one-meter or one-foot design width, so Cb = 1.0.
For wall panels supported by floor panels, you can choose to use the one meter design width for cases that the floor is continuously supported beneath the wall, or you can choose to use the wall depth, for cases that the beam supports the wall without a continuous support below. In this case, a Cb factor is calculated.