Note: Reference is made to images and figures in part one. See June 2023 issue.
Bridge superstructure
While the two bridges are supported by the same massive concrete piers, they were originally independent superstructures. The road bridge was wider than the railway bridge, accommodating two lanes of traffic, one in each direction, whereas the railway was single track, but was stronger since it was required to carry heavy locomotives (relative to motor vehicles).
These two bridges have been modelled in different ways. The model road bridge is located between the railway bridge and the backboard. Its girders are completely covered by the roadway and it is impossible to see them from any normal viewing position. Consequently, the girders for the road bridge were not modelled in detail. However, the railway bridge is in full view of the onlooker, has an open deck without ballast and the internal bracing between its two plate girders can be seen by an observant viewer. So, in this case most of the individual structural members had to be modelled.
The road bridge superstructure was formed from a piece of dressed pine wood about 12.5mm thick and having a width equal to the width of the bridge deck. While the five prototype bridge spans are independent, simply supported structures, in the model the piece of wood forms a continuous beam which
