Summary
A small model of a box beam bridge was tested for its load distribution properties. The distribution was determined experimentally by deflexion and strain readings.
The material used in the construction of the model was Xylonite, a cellulose-base material of Young's modulus 33·33 × 104 lb/sq.in. and modulus of rigidity 11·7 × 104 lb/sq.in.
The experimental distribution of deflexions and longitudinal bending moments proved to be in close agreement with the distribution given by a theoretical treatment involving distribUlion factors. The distribution patterns were found to be virtually unaffected by changes in the longitudinal position of the load.
On the other hand, there were large discrepancies between the experimental and theoretical transverse bending moments. The discrepancies were almost certainly due in part to the small absolute values of the bending moments, which were only about 40 per cent of the corresponding longitudinal moments, and to their high rate of variation across the transverse section both in magnitude and sense. Nevertheless, it was confirmed that the maximum transverse moment occurs at the centre of the bridge when the load is at its position of minimum eccentricity. Further investigation into the distribution of transverse moments will be made on suitably designed models.
