State Bridge Load Posting Processes and Practices (2014) / Chapter Skim
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Pages 26-50
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From page 26... ...
27 chapter three METHODS OF EVALUATION OF WEIGHT LIMITS FOR BRIDGES AND CULVERTS Chapter three presents details on the legal loads, overweight permit loads, methods of load rating, load rating vehicles, and posting levels used by U.S. states.
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28 States establish load limits for single axles, tandem axles, and GVW. States generally adopt the limits set in USC Title 23 for interstate highways, including grandfathered provisions and exceptions for weight limits for some vehicles or route segments.
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29 TABLE 46 LEGAL SINGLE AXLE LOADS, NON-INTERSTATE HIGHWAYS State Axle Load, k State Axle Load, k State Axle Load, k Alabama 20 (7) Louisiana 20 (96)
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30 bridge formulas allow greater GVW than the federal bridge formula. Exempt Vehicles States exempt specific vehicles from some limits on load.
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31 their production, must be moved among sites. Exempt owners are public utilities and government agencies such as fire departments.
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32 cles, and direct permit holders to use these routes. State inventories of bridges and culverts are seen to have three classes of structures; structures that can carry permitted overweight vehicles, structures that can carry legal loads only, and structures, posted for load, that cannot carry full legal loads.
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State Configuration Load (lb) Georgia (57)
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34 and can issue overweight permits without further analysis. These loads are "routine" from the perspective of the state bridge load rater.
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35 North Dakota (72) Trucks, combination vehicles 24,000 Cranes, truck-mounted equipment 30,000 Self-propelled workover rigs 30,000 Self-propelled workover rigs "SE" 31,200 Earthmoving equipment 52,000 Ohio (136)
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36 State Configuration Load (lb) California (123)
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37 State Configuration Load (lb)
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TABLE 57 (continued) State Configuration Load (lb)
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TABLE 57 (continued) State Configuration Load (lb)
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40 State Configuration Load (lb) Oregon (74, 137)
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41 Thirty-four states use more than one basis, with 18 using all three bases. Several states retain LFR and ASR load ratings for existing structures, and apply LRFR to newly designed structures.
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42 distribution in the structure; proof load tests are applied to reach load effects at the level of the operating rating (84)
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43 redundancy. Five states post at the inventory rating, and four use AASHTO's posting equation (Eq.
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44 Structures Rating Method Posting Level Bridges, Generally ASR Using allowable stress = 0.68Fy LFR 0.86 Bridges in commercial zones Load path redundant & ADT < 1000 & no fatigue sensitive details Load path redundant & ADT < 200 Source: Load Rating of Non-State System Bridges (161)
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45 TABLE 67 TEXAS LOAD POSTING LEVEL, ON-SYSTEM STRUCTURES Load Rating General Condition Ratings Inspection Interval, mos Load Posting IR HS20 -- 24 None required OR HS20 Item 58 4 Item 59 5 Item 60 5 or Item 62 5 24 None required HS10 OR < HS20 Item 58 4 Item 59 5 Item 60 5 or Item 62 5 24 Post at operating level HS10 OR < HS20 Item 58 < 4 or Item 59 < 5 or Item 60 < 5 or Item 62 < 5 24 Post at inventory level IR HS3 and OR < HS10 -- 24 Post at inventory level IR < HS3 and OR HS3 Bridge programmed for rehabilitation or replacement 61 Post at operating level or close bridge IR < HS3 and OR HS3 Bridge not programmed for rehabilitation or replacement -- Close bridge OR < HS3 -- -- Close bridge Source: Bridge Inspection Manual (39)
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46 TABLE 68 TEXAS LOAD POSTING LEVEL, OFF-SYSTEM STRUCTURES Load Rating General Condition Ratings Inspection Interval, mos Load Posting IR HS20 -- 24 None required OR HS20 Item 58 5 Item 59 6 Item 60 6 or Item 62 6 24 None required HS10 Item 58 5 Item 59 6 Item 60 6 or Item 62 6 24 Post at operating level HS10 Item 58 < 5 or Item 59 < 6 or Item 60 < 6 or Item 62 < 6 24 Post at inventory level IR HS3 and OR < HS10 -- 24 Post at inventory level IR < HS3 and OR HS3 Bridge programmed for rehabilitation or replacement 61 Post at operating level or close bridge IR < HS3 and OR HS3 Bridge not programmed for rehabilitation or replacement -- Close bridge OR < HS3 -- -- Close bridge Source: Bridge Inspection Manual (39)
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47 Table 71 lists axle counts, wheelbase, and GVW for AASHTO legal load rating vehicles and for AASHTO HS20 design vehicles. Table 71 lists the ratio of GVW for rating vehicles to the limit on GVW obtained from the federal bridge gross weight formula (see Eq.
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48 tures can reduce the load capacity of components and must be recognized in the evaluation of load posting. For LRFR, AASHTO provides a condition factor, jc, as one way to include deterioration in load rating computations.
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TABLE 73 SUMMARY -- STATE RATING VEHICLES State/Org. GVW, k GVW Ratio State/Org.
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50 the TRB database on research in progress (164)
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51 products from farms, forests, or mines; and some vehicles owned by public utilities or state or local governments. Vehicles that exceed limits on legal loads routinely travel on U.S.
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