Building the Arnhem Bridge Perimeter - Part Two - The Bridge Ramp

 Part One 

The printer continues whirring away printing perimeter buildings, which leaves me time to consider how to build the bridge embankment and ramp. I will not be able to fit the entire length of the ramp on the table, but will fit in the most important part including the Van Limburg Strum School. Given the ramp takes the road from street level up onto the bridge I have been busy calculating the road height at different distances along the ramp. In order to fit things in while keeping the overall look of the bridge approach I have decided that the grass embankment will have an incline of 2.5 degrees, while the bridge itself (up to the centre) has an incline of 1 degree. Setting these allows me to ensure the road and flanking building heights are correct in relation to each other, and that I have a guide for building the embankment and its various slopes. 

If my calculations are correct the road surface is 60mm above the table top at the point where the steps up from the underpass meet the road, and is 25mm above the table top as it leaves the board edge at the north end. Establishing these height has allowed me to model the steps and and basic underpass, which in turn has allowed me to start understanding the shape of the embankment in this area. I plan to build the bank itself from layers of 5mm foam sheeting I have sitting in the garage.

I have an ancient copy of Lightwave 3D which allows me to build basic 3d models which I can then convert to STL files and print. Building the steps in Lightwave was an easy way to understand their shape and space that they occupy. The step model is 65mm high at the southern end of the underpass, that being its highest point and 60.014mm at the steps themselve. The steps are 510mm wide when mirrored on both sides of the road which I have set at 150mm wide. This is a little narrower than it should be at 1:100 but is a concession I have made to fit everything in that I want on the map. In rough terms this means the ramp and flanking steps are 20 inches wide, leaving me 28 inches of table width at that point to play around with - perfect !

I need to refine the underpass further, but am happy that I am close to getting the design finalised and that the heights are established and are correct with regard to the buildings that will flank it.