Page 188 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 4 AN ANALYTICAL APPROACH TO FRACTURE AND FAILURE 163

Table 4.4 Comparative study of single span HS-20 moments and shear forces.AASHTO and simplifi ed
formula developed by the author.
HS-20 LL Moments HS-20 LL Shear
Span AASHTO Mmax = AASHTO Vmax =
Length LL Moment 18(L-1.55) (L-14)/L Reaction/Shear 24(3L-28)/L
(Feet) (Kip-Ft) (Kip-Ft) Force (Kips) (Kips)
1. Small spans
20 160 281 distance between outer 41.6 > 36 k vehicle,
axles > 201 formula N/A not correct
30 282.1 273.12 49.6 49.60
40 449.8 449.87 55.2 55.20
2. Medium spans
50 627.9 627.91 58.5 58.56
60 806.5 806.61 60.8 60.80
70 985.6 985.68 62.4 62.40
80 1164.9 1164.98 63.6 63.60
90 1344.4 1344.44 64.5 64.53
100 1524.0 1524.01 65.3 65.28
110 1703.6 1703.65 65.9 65.89
120 1883.3 1883.36 66.4 66.40
3. Long spans
130 2063.1 2063.10 67.6 66.83
140 2242.8 2242.89 70.8 67.20
150 2422.704 67.52
160 2602.54 67.8
170 2782.40 68.06
180 Lane load with 2962.27 Lane load with 68.27
18 kips 26 kips
190 3142.16 68.46
concentrated concentrated load
200 load for bending 3322.05 for shear governs 68.64
210 governs 3501.96 68.8
220 3681.88 68.95
230 3861.80 69.08
240 4041.73 69.2

4.12 SELECTION OF STEEL GIRDERS
4.12.1 Selection Based on Shapes
In practice, the following three types of steel girders are used:
1. Rolled sections.
AISC Manual of Steel Construction lists a wide range of grades 36, 50, and 50W (weather-
ing steel) sections. Sections for grade 70W are not currently available. Since available depth
of steel form is restricted to 42 inches, the application has been to smaller bridge spans only.
LRFD increased live load, and deflection requirements are the constraints. Older bridges

have used 36-inch depth rolled sections whenever possible.