Practice Quiz 8
Note: A one page (one sided) crib sheet is allowed during the quiz,
along with a silent, non-programmable calculator.
Clearly show your work and answer.
A lintel beam 18 ft long is used in carrying the imposed loads. It is a built up section 8.125โ
deep of 3 x 8 sides with a 2 x 2 top (2 nails) and a 7/8 x 12 plywood bottom (4 nails) as shown.
The centroid and moment of inertia for bending about the x axis is given in the figure.
Find:
a) the maximum bending stress for the
section, fb
b) the required shear capacity of the nails for
the top [or bottom] connected part if the pitch
spacing is 5.75 inches
c) the maximum deflection in the beam knowing
E = 1.5 x 106 psi
d) [some short question from the text material]
Answers:
a) fb = 2256 psi
b) F โฅ 168.3 lb [or 361.2 lb]
c) ฮmax = 1.61 in
18 ft
w =520 lb/ft
2.34 k
2.34 k
V
M
14.0 k-ft
7.25โ
2-3x8 (2.5โx7.25โ)
with a 2x2 (1.5โx1.5โ)
2.5โ 2.5โ
8
7โx12โ plywood
1.5โ
12โ
y
ห= 3.76 in
Ix = 325.0 in4
cross section
0.875โ
1.5โ
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