Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Properties of Form Material 79
Size of
Lag Screw
Unthreaded
Shank Dia., in.
Species and Specific Gravity of Wood
Southern Pine
S.G. = 0.55
Douglas
Fir-Larch
S.G. = 0.50
¼ 260 225 179
5
⁄16 307 266 212
³⁄8 352 305 243
7
⁄ 16 395 342 273
½ 437 378 302
5
⁄8 516 447 357
¾ 592 513 409
7
⁄ 8 664 576 459
Hem-Fir
S.G. = 0.43
Note:
1. See NDS [1] for additional adjustments that may be required.
Lag Screws Withdrawal Design Values into Side Grain of Main
Member, lb per in. of Thread Penetration
TABLE 4-25
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not include the length of the tapered tip. For lag screws installed in
the end grain, the values shown in Table 4-25 should be multiplied
by 0.75.
Lateral Resistance of Lag Screws
For wood-to-wood connections, the lateral resistance of lag screws
depends on the depth of penetration, the diameter and bending yield
strength of the screw, and the dowel bearing strength of the wood.
The NDS provides equations for calculating the lateral design values
of lag screws in wood-to-wood connections and for wood-to-metal
connections. The lowest result of the equations is the lateral design
value. Design values are based on dry wood, less than 19% moisture
content, and a normal load-duration.
Table 4-26 provides design values for lateral resistance of lag
screws in wood-to-wood connections for several thicknesses and species
of wood. These values are for lag screws inserted into the side
grain of the main member with the lag screw axis perpendicular to
the wood fibers. The values are based on a penetration, not including
the length of the tapered tip, into the main member of approximately
eight times the shank diameter. If the penetration is less than this
amount, an appropriate adjustment must be made in accordance with
the NDS requirements. The values in Table 4-26 are based on an edge
distance, end distance, and spacing of lag screws of four times the
diameter of the lag screw.
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