Nail Withdrawal Design for C&C Loads

Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.

1. Withdrawal Calculation

   The program no longer implements WFCM 1995 Supplement Table 7A for nail withdrawal design values, and now uses NDS Eqn. 11.2-3 and Table 10.3.1

   W = 1380 C_D C_M C_T G^2.5 D

   where W is the capacity per nail G is the specific gravity of the framing material, and D is the nail shank diameter, C_D is the load duration factor, C_M the wet service factor, and C_T the temperature factor.

   1. Nail Diameters

      For box and common wire nails, nail diameters used are those given in Table A1 of SDPWS Appendix A. Casing nails have the same diameter as box nails of the same size. Roofing nails for fiberboard have a 0.120” diameter given in Table 4.3A.

   2. Specific Gravity G

      The specific gravity is determined by the existing inputs in the program for framing material species and, for MSR/MEL, grade as well. Previously, specific gravity was taken into account by WFCM by using publishing separate values for 3 ranges of specific gravity. The new procedure provides a continuous variation of W with respect to G.

   3. Load Duration Factor C_D

      The load duration factor C_D as input in the Design Settings is applied to the equation. Previously, the WFCM table included a 1.6 factor, and the values were adjusted for the difference between the input value and 1.6.

   4. Service Factors C_M and C_T

      The factors C_M and C_T were already being applied to the WFCM values using NDS Tables 10.3.4 and 10.3.3, and the inputs for moisture content and temperature in the Design Settings.

2. Deformed Nails

   The program now allows you to indicate whether nails are deformed (spiral or threaded – see ), so that they use the higher deformed nail withdrawal resistance values.

   1. Nail Withdrawal Capacity

      The values used are derived from NDS Eqn. 11.2-3, using a diameter one size larger among the list of diameters in table 11.2C than the actual nail diameter. This is the procedure AWC used to generate the threaded nail values in Table 11.2-C.

   2. Roofing Nails for Fiberboard

      Although roofing nails are not included in Table 11.2-C, the same procedure was adopted and the withdrawal value for 0.131” diameter nails is used for 0.120” roofing nails. 0.131 was chosen because the value for threaded nails in 11.2C shows 82 for .012, which is the value for 0.131 diameter unthreaded nails. This was confirmed with AWC to be correct.