A Wood Fastener Withdrawal connection consists of a Main Member and a Side Member connected to one another using a single dowel-type fastener.  The Main Member is a solid wood member, while the Side Member can be defined using either wood or steel material.

Design Considerations

Fastener Withdrawal connections are checked per the American Wood Council, National Design Specification for Wood Construction, 2018 edition (NDS). VAConnect checks the following limit states for Wood Fastener Withdrawal connections (refer to the program’s detailed reports for specific code references):

• Fastener Withdrawal
• Fastener Head Pull-Through

The Adjustment Factor Reports show details of how each factor is calculated.  Individual Adjustment Factors can be ignored (C = 1.0) or overridden using the Project Settings.

Fastener Types

VAConnect considers the following fastener types.

• Lag Screws
• Wood Screws
• Nails - Smooth Carbon
• Nails - Smooth Stainless Steel
• Nails - Roof Sheathing Ring Shank
• Nails - Post Frame Ring Shank

Withdrawal

The Adjusted Withdrawal Design Value (W') is determined using NDS Section 12.2 and the appropriate Adjustment Factors (C-factors), as shown below.

W' = W × CD CM Ct Ceg Ctn

where:

CD, Load Duration Factor - NDS Section 11.3.2

CM, Wet Service Factor - NDS Section 11.3.3

Ct, Temperature Factor - NDS Section 11.3.4

Ceg, End Grain Factor - NDS Section 12.2, 12.5.2

Ctn, Toe-Nail Factor - NDS Section 12.5.4.1

Head Pull-Through

For models with a wood Side Member and round head fasteners (not Lag Screws), pull-through of the fastener head from the Side Member is considered using NDS Section 12.2.5. The Adjusted Reference Pull-Through Design Value (WH') is determined by calculating the appropriate Adjustment Factors (C-factors), as shown below.

WH' = WH × CD CM Ct

where:

CD, Load Duration Factor - NDS Section 11.3.2

CM, Wet Service Factor - NDS Section 11.3.3

Ct, Temperature Factor - NDS Section 11.3.4

Design Assumptions

VAConnect makes the following design assumptions for Wood Fastener Withdrawal connections:

• Members must be in contact (i.e. no gaps).
• Members cross sections must be solid material.
• The fastener diameter and main member specific gravity must be within the ranges given in NDS Tables 12.2A through 12.2E.
• The fastener head diameter and side member thickness must be within the range given in NDS Table 12.2F for the Pull-Through limit state.
• The head pull-through limit state is not checked for Lag Screw fasteners since they do not have round heads.
• Installation requirements outlined in NDS Section 12.1 and 12.2 are assumed to be met.
• When the fastener is inserted in the side grain of the member, the axis is assumed to be perpendicular to the wood fibers.
• When the fastener is inserted in the end grain of the member, the axis is assumed to be parallel to the wood fibers.

Limitations

• The Main Member material must be wood.
• The Side Member material can be either wood or steel.
• The tensile strength of Lag Screw (NDS 12.2.1.4) and Wood Screw (NDS 12.2.2.5) fasteners at the net section shall not be exceeded when loaded in withdrawal. This requires additional consideration by the designer.
• The fastener length must be at least 2x the diameter.