Effect of Truck Weight on Bridge Network Costs (2003) / Chapter Skim
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4CHAPTER 2 FINDINGS Trucks were first manufactured in the United States in 1898 (Rudra http://www.marion.lib.in.us/history/indtrucks/ report.html)
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5This study represents an early effort in this area when many data and methods used today were not available. The basis of the overstress criteria was not documented, and they are certainly different from those used in more recent studies below.
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2.1.5 Study by IIT for Illinois DOT Since increasing the state truck weight limits in 1983, from 326 kN (73,280 lb) to 356 kN (80 kips)
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These responsibilities are applicable to federal expenditures on highway bridges. Four groups of costs were covered: new bridges, bridge replacement, major bridge rehabilitation, and minor bridge rehabilitation.
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Australia to estimate cost impacts for possible increases in truck weight limits. Only existing bridges were considered.
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bridge related data, etc.)
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10 3. Deficiency due to overstress for existing bridges, and 4.
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Based on quantitative understanding of fatigue behavior by physical testing, current AASHTO bridge design and evaluation specifications include provisions covering this subject (AASHTO 1994, 1996, 1998)
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where K is a constant, and Weq,j is then the equivalent weight of vehicle class j that provides the same fatigue damage as the vehicles of that particular vehicle class. The magnitude of Weq,j is sometimes referred to as the fatigue truck weight and equals the cube root of the sum of the cubes of the truck weight distribution.
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tion's lateral distribution factors may be used. These formulas have recently been changed in the AASHTO LRFD Bridge Design Specifications (1998)
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WIM stations will need to be examined to determine how much influence separating trucks into individual classes and doing an individual damage sum will cause to the variation in fatigue life estimates. This influence may or may not warrant a change in the fatigue truck model.
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2.3.2 RC Deck Fatigue RC bridge decks are commonly used in highway bridges in the United States. They provide the driving surface and also transfer wheel loads to the supporting beams or stringers.
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16 TABLE 2.2 RC bridge deck performance comparison (RC box girder bridges)
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mechanism is similar to steel fatigue discussed above. Worse yet, the wheel load movement across a deck causes rubbing of the two concrete surfaces of the crack, widening it and accelerating deterioration.
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18 TABLE 2.3 RC bridge deck performance comparison (RC slab bridges)
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under the new loading requirement. These bridges are then said to be deficient under the new truck weight limits.
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percentage of incremental cost may provide as much as 25 percent increase in truck-load-carrying capacity (e.g., from HS-20 to HS-25)
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bridge design load conceptually is supposed to cover current and future truck loads for the expected life span of the bridges to be designed. When a truck weight limit change triggers truck weight spectra to change, the bridges to be designed according to the current design load may become inadequate because the current bridge design load may not cover the new loads resulting from the truck weight limit change.
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to the rating live load factor in Eq. 2.3.3.1 except that the factor "t(AADT)
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in payload ton-miles carried by trucks would be expected (since the cost of transportation is decreased by an increase in PMGVW) , the implicit assumption likely overstates the size of this increase.
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Changes in the violation rate (such as might be caused by stricter enforcement of truck weight laws) also affect the weights of all laden trucks, including those that are operating at weights substantially below current limits.
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