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Unformatted text preview: 1.39 Member ABC, which is supported by a pin and bracket at C and a cable BD, was
designed to support the 4kip load P as shown. Knowing that the ultimate load for
cable ED is 25 kips, determine the factor of safety with respect to cable failure. PROBLEM 1.39 SOLUTION P
1‘ Use member ABC as a. A
T ¥v~ee book, and “0+3 1
15m. chul' mem ber 80 is a +wc> — ‘Force. mem lo if L______’ 12in.—l ZMC = O 18 in. <9 M, Mtaom + LP swowss») — we» snow
03» SM 3o‘)(,2 tn) = o _ 32.0.3 _ 32.c23)(t+) _ .
F»  m?  W  5°87" kw
Fu‘l’or ol' sa‘Fe‘l‘y 'Fbl‘ cwlale 30 PS. = TEESit: = 3:82:75— : 3.G9 ‘ 1.40 Knowing that the ultimate load for cable ED is 25 kips and that a factor of safety
of 3.2 with respect to cable failure is required, determine the magnitude of the largest
force P which can be safely applied as shown to member ABC PROBLEM 1.40 SOLUTION Us: member ABC as a.
Free. boar anA no‘l'? 'th‘l‘ member 8D is G.
ﬁnaleForce. men he». ZMcto (Peas 90°)(3O l“) +(P5M 40°)(15;..) 7', (Fan Cos 30°)(l5in3
" (Fm, Sin 30°)(l2 [va : o _ \8.QQo _
P — ”37213? FED _ 0.58216 F”
.' . ,, i‘, F _ _E‘)£’  as. ‘ kn
Ap/owabie penal ‘POI‘ member 80 IS 31,  F5 — ET_ 7.8)25 ups Nﬂouab/e local P = (0.582IC )(7.3l25') =' 4.55 kips PROBLEM 1.41 1.41 Members AB and AC of the truss shown consist of bars of square cross section
made of the same alloy. It is known that a 20 mm square bar of the same alloy was
tested to failure and that an ultimate load of 120 kN was recorded. If bar AB has a 15
mm— square cross section, determine (a) the factor of safety for bar AB, (b) the
dimensions of the cross section of bar AC if it is to have the same factor of safety as bar AB. 0 .4m . B—L SOLUTION LenaHi a? member AB
9M3 ’' _/B752+ 62f: = 085 m
use en+fre +V‘uss as a ‘Free Boaiy A. TAAY DEMcro m A“  (0.7:)(283 = 0 Ar 15 W $2520 A,—22=o A1=22uN 3
Use Joia‘l‘ A as "Free boaly 2‘ lcN
Ax A, LZFﬁo ﬂag—Ape c c
FAB AB :(ocﬁ'gls) = ,7 kN
F“ HEP71:0 Ara35:3; For H‘e +es+ loam A r (0.02.0)a T QOOYID" m" Pa = WONGa N   P  Mow/03 __ s
For He mdenaﬂ 6”  A‘u  W5 — 300x") PG. (a) Foo bar A8 E3: f;  GLA = soowo‘ (0.015),.I ﬁe ' Fm a7x/o
= 3.77 ..
(b3 For bar AC ES. : E"— : M ._. 6230.1
5" FA: ﬁt.
a}: $5255 ._. (3.97)§20xlo‘) = 24:47 “0; M:
6?; aooxlo‘ (1.: 16.2%1/0'3 m ...
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 Fall '09
 MOORTHY

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