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Unformatted text preview: 05Ch05.qxd 9/24/08 412 4:59 AM Page 412 CHAPTER 5 Stresses in Beams (Basic Topics) Solution 5.5-25
(a) RESULTANT LOAD F ON SIGN
s 12.5 in. p 20 psf b 360 p
180 A b
cot a b
2 b n L 0.785 rad pA F 72 in. c1 8 0.769 in. A 754.442 in.2
sc c2 FL Mmax
sc 0.731 in.
; 36.0 ksi (max. bending stress at base of post) ; 104.8 lb 0.16101 in.4 IZ Mmax c1
Iz Mmax 5.239 ft2 or A
F (b) MAX. BENDING STRESS IN POST st Mmax c2
Iz st 34.2 ksi Design of Beams
P Problem 5.6-1 The cross section of a narrow-gage railway
bridge is shown in part (a) of the figure. The bridge is
constructed with longitudinal steel girders that support the
wood cross ties. The girders are restrained against lateral
buckling by diagonal bracing, as indicated by the dashed lines.
The spacing of the girders is s1 50 in. and the spacing
of the rails is s2 30 in. The load transmitted by each rail to a
single tie is P 1500 lb. The cross section of a tie, shown in
part (b) of the figure, has width b 5.0 in. and depth d.
Determine the minimum value of d based upon an
allowable bending stress of 1125 psi in the wood tie.
(Disregard the weight of the tie itself.) P s2 Steel rail
girder (b) s1
(a) Solution 5.6-1 Railway cross tie
S bd 2
d 50 in. b depth of tie 5.0 in.
P s2 1500 lb Solving, 30 in.
sallow 1125 psi s2) P(s1
2 15,000 lb-in. 1
(50 in.)(d 2)
s allow S
16.0 in. 5d 2
6 d (1125) a
dmin NOTE: Symbolic solution: d 2 inches
6 4.0 in.
bsallow ; ...
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This note was uploaded on 12/22/2011 for the course MEEG 310 taught by Professor Staff during the Fall '11 term at University of Delaware.
- Fall '11