United States Department of Transportation
i
Monitoring System to Determine the Impact of Sugarcane Truckloads on Non-interstate Bridges [Final Report]
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2008-12-01
[PDF-1.92 MB]
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Abstract:The study included in this report assessed the strength, serviceability, and economic impact caused by overweight trucks hauling sugar cane on Louisiana bridges. Researchers identified the highway routes and bridges being used to haul this commodity and statistically chose samples to use in the analysis. Approximately 84 bridges were involved in this study. Four different scenarios of load configuration were examined:
1. GVW = 100,000 lb., with a maximum tandem load of 48,000 lb.,
2. GVW = 100,000 lb., with a maximum tridem load of 60,000 lb.,
3. Uniformly distributed tandem and tridem loads, and
4. GVW = 120,000 lb., with maximum tandem of 48,000 lb., and maximum tridem of 60,000 lb.
It is to be noted that a GVW of 120,000 lb. for sugarcane haulers was the highest level currently considered in this investigation. The methodology used to evaluate the fatigue cost of bridges was based on the following procedures: 1) determine the shear, moment, and deflection induced on each bridge type and span, and 2) develop a fatigue cost for each truck crossing with a) a maximum GVW of 120,000 lb., and b) a GVW of 100,000 lb. with a uniformly distributed load.
Through the use of a field calibrated finite element model, Structure 03234240405451 was analyzed and load rated for loading vehicles HS-20, 3S2 and 3S3 (sugar cane loading cases 1 thru 4). The structure had adequate strength to resist both bending and shear forces for all six loading vehicles. It should be noted that all of the rating factors were acceptable for all 17 spans as long as the construction and the structural condition of each span were the same.
Results indicate that among the four cases of loading configurations, Case 4, which was a GVW=120,000 lb. with maximum tandem and tridem loads, generated the worst strength and serviceability conditions in bridges. Therefore, Case 4 is the loading configuration that controls the strength analysis and evaluation of fatigue cost for bridge girders. Based on the controlling load configuration, Case 4 with a GVW = 120, 000 lb., the estimated fatigue cost is $11.75 per trip per bridge. In Case 3, which was a GVW = 100,000 lb. uniformly distributed load; the estimated cost is $0.90 per trip per bridge.
The results from the bridge deck analyses indicate that the bridge deck is under a stable stress state, whether the stresses are in the tension zone or the compression zone. Moreover, the decks of bridges with spans longer than 30 ft. may experience cracks in the longitudinal direction under 3S3 trucks. Such cracks will require additional inspections along with early and frequent maintenance.
Based on the results of the studies presented in this report, it is recommended that truck configuration 3S3 be used to haul sugar cane with a GVW of 100,000 lb. uniformly distributed. This will result in the lowest fatigue cost on the network. It is recommended that truck configuration 3S3 not be used to haul sugar cane with GVW of 120,000 lb. This will result in high fatigue cost on the network and could cause failure in bridge girders and bridge decks.
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