Internal Forces in a Reinforced Concrete Box Culvert

In 1996, a reinforced concrete box culvert with approximately 19 meters of embankment fill was instrumented with strain gages and pressure cells to determine the internal forces applied to the culvert. Strain and pressure readings were taken for a period of 3 years during and after the construction of the embankment. From a knowledge of the culvert's dimensions and material properties, the strain readings were converted to forces and bending moments. These forces were then compared to the allowable criteria from the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. A computer model of the culvert was performed to compare the results of the strain gages and pressure cells to the unit weight of the embankment fill. The computer model was also used to study the changes in internal forces due to different boundary conditions.

The results showed that axial forces and bending moments are linearly related to the embankment fill height. The box culvert has adequate capacity according to the design equations from AASHTO. Computer modeling of the culvert showed that the effects of different boundary conditions give slightly different moments in the roof and the wall. Load distributions on the roof show very little change in bending moments and shears, but when the load distribution on the wall increases on the bottom, a significant increase in shear forces is seen.