Another Bridge

Very little has happened outside recently.  Since getting back after a week away on holiday the weather has not been conducive to concreting and mortaring.
I have designed the next bridge which will be a 1.25m under arched girder bridge.  It proved to be a little more difficult than I had anticipated as I didn't know how to calculate the radius of the arch, but a Google search led me to http://www.mathopenref.com/ which provided the following information.

Given an arc or segment with known width and height:

The formula for the radius is:

where: W  is the length of the chord defining the base of the arc H  is the height measured at the midpoint of the arc's base.

I've started cutting the aluminium which was left over from the last bridge, but work has now stopped until I can get more supplies.

The plan for the next bridge