Bridge Rating Practices and Policies for Overweight Vehicles (2006) / Chapter Skim
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From page 4... ...
Bridge evaluation for permit review is very similar to bridge load rating. Both are used to understand the bridge's safe load carrying capacity, with the former targeting the permit vehicle as the reference and the latter referring to some standard vehicle loads meant to represent the general truck traffic.
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Thus, bridge evaluation for overweight permit review typically replaces the standard vehicle load's load effect LL with the permit vehicle's load effect in Eq.
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. There have been discussions on whether using these live load factors for permit review is appropriate, because the bridge evaluation for permit focuses on the FIGURE 2 AASHTO standard H20 vehicle live load: (top)
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of Highway Bridges 2003] has adopted a probabilistic concept of prescribing different load factors for the standard bridge load rating and the bridge evaluation for permit review.
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NCHRP Synthesis of Highway Practice 143: Uniformity Efforts on Oversize/Overweight Permits 1988. This synthesis study focused on the uniformity efforts in OS/OW permit issuance.
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These live load factors are different for single trip permits and multitrip (e.g., annual) permits.
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The procedure was derived using theoretical assumptions regarding the probability distribution of the truck 0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 1997 1998 1999 2000 2001 2002 2003 0 500000 1000000 1500000 2000000 2500000 3000000 2001 2002 2003 Non-Divisible Single Trip Permits Non-Divisible Annual Permits Divisible Single Trip Permits Divisible Annual Permits Overwidth Permits FIGURE 5 Number of overweight/overwidth permits issued by states. FIGURE 6 Overweight/overwidth permits issued by states by type.
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Statistically, the annual permits represent significantly more trips than the single trip permits. Therefore, the annual permit vehicles may appear much more often on the roads.
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