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Notch design has been expanded and improved significantly, with the addition of interior notches, notches on sloped members, and more accurate calculation of the notch factor KN.
Interior Notches (v9 - Feature 14)
The program now allows for notches to be located at interior supports in multi-span and cantilevered members. This allows for common situations such as a birds-mouth notch in a roof rafter, especially in conjunction with improvements made in the treatment of notches for sloped members (see immediately below). .
Restrictions
Interior notches can be notched at the lower surface only; top notches are not allowed.
According to the USA National Design Specification (NDS), the stiffness of a bending member is practically unaffected by notches with depth less than or equal to 1/6 beam depth and length less than or equal to 1/3 beam depth. Accordingly, these limits have been applied to interior notches.
Input
The input fields that were previously in their own data group have been moved to the Supports for bearing design data group\. which has been renamed Supports for bearing and notch design. The control for Left end, Right end, or Both has been eliminated. Instead, the mechanism for choosing supports for bearing design is now also used to choose the supports for notch input. That is, the control Applies to is used to specify the support(s) that the notch inputs apply to.
Notch length input for interior notches assumes notch is centred at support, that is, there is equal unsupported notch length on either side of the support.
The program rejects input of interior top notches and resets the input fields without notifying you.
Shear Design
Shear design is performed using 5.5.5.1 with net area An, and for tension forces which are almost always present in bottom notches, 5.5.5.3 and 5.5.5.4. These procedures had already been implemented for end notches.
When calculating the notch factor KN in 5.5.5.4, e is simply one-half the notch length; the minimum required bearing is not used for interior notches.
Moment Design
For interior notches, the program uses the net area to calculate the section modulus S in the calculation for moment resistance using 5.5.4.1. Note that this had not previously been required for end notches because moments at the end are zero.
Notch Size Limitations
If the input notch exceeds the notch size limitations, upon design the program:
Issues a warning on the screen
Designs with shear resistance given in the Design Check results as “N/A”
Shows a failure warning in the Design Check due to notch restrictions
Output
The notch output in the Materials Specification of the Design Check report is now formatted in a similar manner to supports for bearing design, that is, the supports are numbered sequentially from the left and of the beam and the information for the notch given after the support number if there is a notch for that support.
Notches on Sloped Members (v9 - Bug 2789)
The program now considers the slope angle of the beam when drawing and designing for notches in sloped members.
Background
The program did not consider the slope of the member in determining the values of e and dn from for sloped members, so that for the purposes of design, the input notch length and depth are measured parallel and perpendicular to the member as shown in Figure 5.5.5.4. However, when the notch length = bearing length option is used, the support length is the projected length measured horizontally, and the minimum bearing length used in 5.5.5.4 for the notch factor KN is also the projected length. The program no longer has this inconsistency.
Input
The input notch length and depth are now considered to be the vertical and horizontal (projected) distances. These correspond to the width of supporting or supporting members that may be the reason for the notch. The horizontal width is used for consistency with the width of supporting or supported members that are often the reason the notch is made..
The depth is defined as the vertical distance, rather than the dn shown in Figure 5.5.5.4, for consistency with the width and because you would ordinarily lay out the notch using a square with the marks on the edge of the wood corresponding to the ratio of rise/run of the sloped member.
Design
Internally, the program converts the input notch length and depth to the values of dn and e shown in Figure 5.5.5.4, and uses these to compute the notch factor in 5.5.5.4 for sawn lumber and 6.5.7.2.2 for glulam.
Notch Depth Restriction
The value dn calculated by the input notch depth multiplied be the cosine of the slope angle is used to check the restriction that notch depths shall not exceed 0.25 of member depth (6.5.7.2.2 and 5.5.5.4).
Drawing (v9 - Bug 2788)
The program now draws notches on sloped so that a member supporting a sloped member fits into a notch entered for that support. Note that for reasons of economy of space on the screen and printed output, the beam angle in the drawing is not always the actual beam angle, so that notches on the drawing often do not penetrate the member as they do the actual beam.
Output
A line has been added to the CALCULATIONS section of the Additional Data of the Design Check report giving the e and dn values for each notch on the member.
Other Notch Input
Input Notch Length Less than Support Length (v9 - Bug 2792)
When notches are added to the bottom of the beam that are less than the support length, the program internally uses the support length as the notch length and shows this notch length on the diagram and in the output; however the input field remained as the value less than the notch length. Now when a support length is chosen, or when design is done for unknown bearing length, or if necessary when the angle of the beam changes, the program updates this value by checking the Support Length checkbox and erasing and disabling the notch length input.
Identifier for Bearing Length used as Notch Length (v9 - Bug 2791)
The input checkbox previously named Minimum bearing length has been changed to Support Length. Minimum bearing length was used before the bearing support length feature was added with Version 8..
Other Notch Design
Length e Used for Notch Factor (v9 - Bug 2790)
In implementing CSA O86 5.5.5.4, for a notch entirely over a support, the program calculates e as the input notch length minus 1/2 the minimum bearing length, when it should be using the lesser of the 1/2 minimum bearing length and 1/2 the notch (or support) length. As a result the value e was usually much larger than it should be, and the notch factor less than it should be. This has been corrected.
Notches that extend past the support also used this erroneous calculation.
A line has been added to the CALCULATIONS section of the Additional Data of the Design Check report giving the e values for each notch on the member. .
Notch Length Limitations (v9 - Change 164)
The length of all notches has been restricted to extending to 1/3 the span length. Previously the notch length had no restrictions, leading to impractical notch lengths that could extend to a neighbouring support, and which would have unaccounted for effects on the stiffness of the beam. The 1/3 span length limit imposed on notches in the USA National Design Specification (NDS),
This limitation is imposed when designing the member, at which time the program automatically adjusts the notch length to the maximum allowable. This change is reflected in the user interface input at that time.
Notches in Tension or Compression For Zero Reaction (v9 - Bug 2090)
When the bearing reaction at a notched support is zero the notch is sometimes considered in tension when it should be in compression and vice versa. Whether the notch is in tension or compression determines whether 5.5.5.1 or 5.5.5.3 is used for notch design for sawn lumber, and for glulam whether 6.5.7.2.2 a) or b) is used. Note that it is quite rare for the mechanics of the beam to be such that the reaction of the support is precisely zero, so this bug is very unlikely to have occurred in a practical design.
Moment Design for End Notches with Applied Moments (v9 - Bug 2845)
The program now uses the net section for moment design when an applied moment is entered right at the end of the member that is notched at the end. Note that this condition is quite rare in practice.
Output
Zero Joist Notch Depth and Length (v9 - Bug 2722)
For joists only, in the materials specification of the Design Check output, the notch depth and unsupported length were showing as zero even though the member designed with the notch depth as input. .
These problems have been corrected.
Format of Notch Depth and Unsupported Length (v9 - Bug 2724)
The notch depth and length in the materials specification of the Design Check output was not showing the units employed, was not formatted using the imperial format style chosen in the Format settings. and it was not showing a decimal place for even numbers, e;g. 2 instead of 2.0. These problems have been corrected.
Notch Factor KN Reported for Non-Critical Load Combination (v9 - Bug 2800)
The KN factor in the FACTORS table of the Additional Data in the Design Check Output was sometimes reported as the one calculated for load combinations where the notch is in tension when for the critical load combination the notches are in compression. This is a reporting error only and the correct KN was used for design.