Page 236 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 5 LOAD AND RESISTANCE FACTOR RATING AND REDESIGN 211

Figure 5.12 Continuous spans alternate live loads, reduce loads by 10 percent.

2. Permit load for Pennsylvania: minimum length of P-82 permit load is 55 ft with 204 kips
weight (Figure 5.15).
AASHTO lengths of permit (notional) loads are 51 ft between the first and last axles with

199 kips weight.
3. Permit load for New Jersey (Figure 5.16).

5.5.6 Comparison of Permit Loads with Cooper E-80 Train Loads.

1. Live loads for railway bridges are many times higher than even the highest of truck loads
requiring a permit. A comparison of moving loads is shown in Figure 5.16 between the latest
New Jersey permit load (790 KN or 180 kips total), cooper loads (Figure 5.17 and 5.18),
1800 kips or 400 kips for alternate load (Figure 5.19).
2. It is interesting to note that a bridge is normally designed for single truck occupancy per
lane but with simultaneous lane load added. Correction factors are applicable to multiple

lanes, with live load modified by applying a factor.
Figure 5.20 shows a comparative study of moments with HS-20 and PA trucks and permit
load P-82.
3. Application of Impact Factors and Multiple Lane Presence Factors
• Refer to AASHTO Section 3.14.14: Impact factors are applicable to truck loads and not

to lane loads. As required in AASHTO standard specifications, no concentrated load is
required in LRFD lane load.

• Unfactored live load analysis is first carried out without impact factors. An impact factor
of 1.3 is applied on truck load elastic analysis. In addition, a multiple lane presence factor
is applicable.

Figure 5.13 Fatigue load truck with constant 14 ft spacing.