Page 190 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 4 AN ANALYTICAL APPROACH TO FRACTURE AND FAILURE 165

Max. Truck Moments Max. Truck Shear/Reactions
Span †
Author’s Formula* Tandem Governing Truck Author's
Length HS-20 Two 25 Kip axles Moments Formula** Tandem Two 25 Governing Truck
(Feet) (Kip-Ft) (Kip-Ft) (Kip-Ft) HS-20 (Kips) Kip Axles (Kips) Shear (Kips)
80 1164.98 950 1164.98 63.6 48.75 63.6
85 1254.70 1012.5 1254.70 64.09 48.82 64.09
90 1344.44 1075 1344.44 64.53 48.89 64.53
Medium spans
95 1434.21 1137.5 1434.21 64.93 48.95 64.93
100 1524.01 1200 1524.01 65.28 49 65.28
105 1613.82 1262.5 1613.82 65.6 49.05 65.6
110 1703.65 1325 1703.65 65.89 49.09 65.89
115 1793.50 1387.5 1793.50 66.16 49.13 66.16
120 1883.36 1450 1883.36 66.4 49.17 66.4
130 2063.10 1575 2063.10 49.23 66.83 HS-20 shear force govern
140 1700 2242.89 HS-20 moments govern 49.29 67.20
150 1825 2422.704 49.33 67.52
160 1950 2602.54 49.38 67.8
Lane load with Lane load with
170 18 kips 2075 2782.40 26 kips 49.41 68.06
Long spans
180 concentrated 2200 2962.27 concentrated 49.44 68.27
190 load for bending 2325 3142.16 load for shear 49.47 68.46
governs
governs
200 2450 3322.05 49.5 68.64
210 2575 3501.96 49.52 68.8
220 2700 3681.88 49.55 68.95
230 2825 3861.80 49.57 69.08
240 2950 4041.73 49.58 69.2
† Tandem load moments exceed 20 moments for long spans.

3. Fabricated girders.
Due to improvements in fabrication technology, lighter girders are possible for a wide
range of spans. It is more economical to use variable thickness flanges and a thinner web

with transverse stiffeners at variable spacing. Welds in tension zones can be avoided.
Max. HL-93 moments are combined truck and lane moments. While maximum lane
moments occur at midspan, maximum truck moments occur under the wheel load. An
approximate method is to combine the two values. The lane moments at the location of
wheel will be smaller due to parabolic shape of bending moment diagram.
With the availability of plates in a wide range, hybrid girders with 70W steel fl anges and
50W webs are now possible. Some states have successfully used 100W steel for longer
spans.

Use of Rolled Sections Versus Plate Girders
When designing a girder, a distinction is found between selections of rolled sections com-
pared to fabricated plate girders. Due to rolling tolerance requirement of thinner webs, rolled