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1 2003

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Verification of live load distribution factors by field testing and analysis

Eom J., Nowak A.

Konstrukcje Stalowe

2003

nr 5 spec.

CD-CD

The paper deals with distribution of truck load on girder bridges. Previous analytical studies based on Finite Element Method (FEM) indicated that the code specified (AASHTO 2003) girder distribution factors (GDF) are inaccurate. In particular, they appear to be conservative for longer spans and larger girder spacing, but too permissive for short spans and girder spacings. Therefore, a field testing program was carried out including 17 steel girder bridges with spans up to 45 m. For each tested structure, girder distribution factors were determined by measuring strains in the girders under heavy trucks. Test trucks were 11 axle vehicles, loaded to the legal limit in Michigan (over 650 kN). The strains were recorded for a single truck, and for two trucks side-by-side. The tests were repeated for crawling speed and normal traffic speed for the location. In all tested bridges, the GDF's determined from the field measurements are lower than code specified values. In addition, the considered bridges were analyzed using a commercial finite element software package, ABAQUS. The analytical results were compared with those from field tests. It was observed that the maximum values of the strain and corresponding stress are lower than analytical values obtained using ABAQUS. The reason for this discrepancy is unintended composite action and partial fixity of supports (rather than simple supports).