Page 235 - Bridge and Highway Structure Rehabilitation and Repair

210 SECTION 2 STRENGTHENING AND REPAIR WORK

End View

Figure 5.10 Standard HL-93 live load.

• Truck pair for negative moments with partial lane load (HL-93 for continuous spans) as
shown in Figure 5.12.
3. Fatigue vehicle: Live load vehicle for fatigue load without lane load per lane:
• HS-20 truck alone with 14 ft fixed axle spacing for evaluating fatigue as shown in Figure

5.13.

4. Deflection vehicle and 25 percent HS-20 truck 4 lane load (alternate defl ection).
Deflection vehicles are as shown in Figures 5.14.

5.5.4 Increase in HL-93 and Tandem Loads

1. In view of the truck traffic, some states such as Pennsylvania have increased HS-20 truck to
HS-25, which is a 25 percent increase. Lane load of 0.64 kips/ft is added to the truck load
without any change.
2. Similarly, tandem loads were increased by 25 percent to two 31.25 kip axle loads spaced 4
ft apart.

5.5.5 Permit/Notional Loads Without Lane Load
1. In addition to HL-93 loads, following special loads need to be considered:
Legal, permit, and military loads: Both the superstructure and foundation need to be
designed to sustain these loads. In earthquakes, all gravity loads including live load on
the bridge contribute to seismic forces and moments. The length of moving vehicle is also
considered to compute design moments and shear forces.

Figure 5.11 Alternate live load for maximum
positive moment.