Page 241 - Bridge and Highway Structure Rehabilitation and Repair

216 SECTION 2 STRENGTHENING AND REPAIR WORK

Truck

B.M. Max
Longitudinal
Moment in
Beam
C.L. of
Beam

S
Figure 5.20 Maximum distribution of beam moment under wheel loads. (Resultant of wheel load coincides with
center line of beam).

5.6 DETAILED AASHTO LOAD COMBINATIONS FOR RATING AND DESIGN
5.6.1 Load Combinations for Rating and Magnitude of Load Factors

1. For load rating, a simplified format is used as compared to LRFD. Only primary loads need

to be considered. Bridges need not be rated for wind and extreme loads.
2. Load factors for legal loads in Tables 6-5 of AASHTO Manual of Condition Evaluation and
LRFR are based on ADTT volume.
3. Load factors for permit loads in Tables 6-6 are based on permit truck weights and ADTT
volume.
4. Service I for permit live loads is optional.
5. Service II for all live loads is applicable to the rating of steel bridges. In addition, optional
fatigue loads without dead loads may be used.

Table 5.4 Load factors for rating of bridges.

Level I Live Level I Live
Load Inventory Load Operating Level II Level III
Limit State Materials Dead Load DC Dead Load DW Rating Rating Legal Load Permit Load
Strength I All 1.25 1.50 1.75 1.35 Table 6.5 N/A
(HL-93)
Strength II All 1.25 1.50 N/A N/A N/A Table 6.6
(Permit)
Service I Reinforced/ 1.00 1.00 N/A N/A N/A 1.00
(Permit) prestressed
concrete
Service II Steel 1.00 1.00 1.30 1.00 1.30 1.00
(All live loads)
Service III Prestressed 1.00 1.00 0.80 N/A 1.00 N/A
(Legal ) concrete
Note: All bridges will be rated for strength I (HL-93) and strength II permit loads.