Unformatted text preview: PROBLEM 5.105 l'.‘l.llll.'5 A bridge oflengthL = 48 ﬂ is to be built on a secondary road whose access to
trucks is limited to twoaxle vehicles of medium weight. It will consist of a concrete
slab and of simply supported steel beams with an ultimate strength q, = 60 ksi. The
combined weight of the slab and beams can be approximated by a uniformly distributed
load is = 0.75 kip/ft on each beam For the purpose ofthe design, it is assumed that a
MWithaxleslocatedatadistanoea= l4 ﬁﬁomeachoﬂlerwillbedriven across the
bridge and that the resulting concentrated loads P, and P, exerted on each beam could
be as large as 24 kips and 6 tips, respectively. Determine the most economical wide
ﬂsnge shape for the beams, usingLRFD with the load factors r0 = 1.25, n = 1.75 and
the resistance factor ¢ = 0.9. [Hint It can be shown that the maximum value of {Mil
occurs under the larger load when that load is located to the left of the center of the beamatadistanceequaltoaP,I2(P1+P2).]
SOLUTION
Decal Poul : 'R, E R3 = (ﬁltmxms) = t8 kip:
Area. A455 of shear 01.1»er (Hams). 2; kipH
Mm = 214 lap—H = 2592 k.,.;... J Paid 5 Live ”and: U = U= 24—1.?
+ = 216114
 G= “lg36$ x
X
L
2 M. = o 43 R. +(2S4X1Hi(HJJHG) = O
P. = H.125 ta... A in, C V ‘1' l‘i. lZS. kilos
C +0 0' V= '4.l1$’ 1‘! : ~9.37$‘ in}?!
D +3 B V '‘ * 15.875 115.95 Ana A lo C (21.004.125) r 3H.22$’ lapH
Benita: maned5 MC: 317.223— k.‘,.H . 333: kw... _3_Desi n= Tm» 7: Mt = (PHI: = 906.33“.
S.. : “Vino +YLML _ (l.2$')(25"72)+(l.7$}(3831) <9 62:: tostteo)
= IB‘L 2 ...
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 Summer '10
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