In: Civil Engineering
A wooden beam is fabricated from one 2 × 12 and two 2 × 12
dimension lumber boards to form the double-tee cross section shown.
The beam flange is fastened to the stem with nails. Each nail can
safely transmit a force of 160 lb in direct shear. The allowable
shear stress of the wood is 84 psi. Assume b1 =
12 in., b2 = 2 in., d1 = 2
in., d2 = 12 in.
(a) If the nails are uniformly spaced at an interval of s
= 2.4 in. along the span, what is the maximum internal shear force
V that can be supported by the double-tee cross
section?
(b) What nail spacing s would be necessary to develop the
full strength of the double-tee shape in shear? (Full strength
means that the maximum horizontal shear stress in the double-tee
shape equals the allowable shear stress of the wood.)