Another bridge for which there is a limited (but necessary) model. You can see the reason I took a diversion to look at this from Google Maps, here. That is a serious skew, about 61 degrees. The railway from Paisley to Glasgow was built under the direction of Joseph Locke. I am not sure whether he did this continuation.
Let’s begin with a simple photograph. I didn’t get one showing the full elevation, as I should, because I was in some haste over a change of trains in Glasgow heading South from Dundee. I needed modelling shots not broad coverage. This is looking East towards Paisley and already gives a clear idea of the skew.
If we move to views from the model we get full coverage but a few patches of missed picture. There is a reduced quality model in Sketchfab which can be viewed in a web browser.
The model was built without the benefit of control survey and is slightly twisted from N to south and bent through the width, but still worthwhile for our purposes.
The square elevation shows both the twist and the curve.
Looking at the West side on the skew is quite remarkable.
The stretch on those spans is remarkable and it becomes clear that the centres were almost certainly erected on the square, producing a segmental arch in the square view and a stretched ellipse on the skew. That difference is much harder to detect with a skew angle even as great as 45 degrees.
An upward view really shows the skew to greatest effect.
The piers look remarkably chunky, which was probably well advised. Drawing square lines on the centre span emphasises that the old rule of “if enough of the abutments face each other, the bridge can be analysed square” is not going to help us here.
Despite the high skew, the bridge seems to be in remarkably good condition. The only major damage is from vehicle impact and that is very restricted on the approach corners. I wonder how many vehicles have tipped here.
Without getting back and looking more closely, I am not able to say whether the lines in the next view are actual damage or an aberration in the model. A crack like that, staggering through the joints on a skew line, is not unheard of though.
This is a short review but time is pressing. I want to finish by noting just how large the voussoir stones are. The van gives a pretty good idea of the scale. The end voussoirs are tightly curved in three dimensions and it would have been the engineers job to create templates to cut them. Notice, too, the many tiny teeth on the skewbacks, each supporting only two courses of brick.
