Date of Award

Fall 2007

Document Type


Degree Name

Doctor of Philosophy (PhD)


Materials and Infrastructure Systems

First Advisor

Aziz Saber


The study included in this dissertation assesses the strength, serviceability, and economic impact of overweight trucks on Louisiana bridges. Truck load configurations FHWA 3S2 and FHWA 3S3 were applied to bridge models that were originally designed for HS20-44 truck configuration to determine the effects of heavy truck loads on bridges. Behaviors of bridge components including bridge girder, deck, and diaphragm were evaluated separately.

AASHTO linear approach and finite element analysis were employed to evaluate bridge girder behaviors under the heavy truck load. Bridge models with different geometric configurations were considered. Both short term and long term effects on simple span and continuous bridges were determined based on AASHTO LRFD specifications. Results indicated that the AASHTO linear approach was more conservative than the finite element approach. Results based on finite element analysis showed that the short term effect of heavy truck load on selected bridge models was limited, while the long term effect was significant.

Finite element analysis was used to perform the bridge deck evaluation. Longitudinal, transverse, and shear stress states at top and bottom surfaces of decks were obtained and evaluated. The researcher determined that bridge decks were overstressed and might experience cracks.

Statistical methods were introduced to this study in order to evaluate stress data of bridge decks. Due to the determinacy of results from finite element models, a modified factorial experiment with crossed treatment factors was created to perform the probability based statistical analysis. The sequence of significance of analysis parameters was observed. Effects of bridge girder types on deck stress performances were discovered under different bridge geometric and truck load configurations.

The diaphragm behaviors were assessed based on ratios of axial forces. The effects of heavy truck load on diaphragms were determined limited even though the ratio exceeded the criteria, since the values of axial forces were not large.

The methodology employed in the evaluation of 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) FHWA 3S2 truck with maximum GVW of 108,000 lb; (b) FHWA 3S3 truck with maximum GVW of 120,000 lb; and (c) FHWA 3S3 truck with GVW of 100,000 lb. with uniformly distributed load.

The researcher recommends that (a) for bridges on the routes of timber, lignite coal, and coke fuel transporting, do not increase the GVW to 108,000 lb. to avoid the high bridge fatigue cost; (b) for bridges on the routes of sugarcane transporting, truck configuration FHWA 3S3 is suggested to be used to haul sugarcane with GVW of 100,000 lb. uniformly distributed. This configuration will result in the least fatigue cost on the network. It is not recommended that truck configuration 3S3 be used to haul sugar cane with GVW of 120,000 lb., which will result in high fatigue cost on the network.