arches

A Cable stayed bridge that isn't

At the end of South Street in Exeter, straddling a gap in the city wall is a bridge that has cables as expensive and dubious decoration.

From here it looks to make some sort of sense (though the relative positions of cable, leg and cantilever end are strange) but the end view begins to confound that.

Here we see that the back-stay cables go straight to the ground straddling the wall, some of which is Roman.

From here you can see how much those cables sag. Natural frequency about 0.5Hz as I recall, easily measured with a watch anyway.

Where does the reaction go though?

Answer seems to be nowhere, or at least in bending into that column so it is well there is no tension to speak of.

Nuff sed?

A failed attempt at flattery

I talk to engineering students about design issues but don't usually get so public (glass houses and all that, and anyway, what have I ever built) but I am pushed by the Happy Pontist and hos BAMPOT, see here https://happypontist.blogspot.co.uk/2017/09/introducing-bridge-awards-for.html.

So here are some thoughts on one Exeter bridge with another to follow shortly. Neither of these looks like a simple engineering job, they look more like an architect taking an unfortunate hand.

They say that imitation is the sincerest form of flattery. In engineering that often means taking a simple idea and polishing it a little.

Was Calatrava’s the first tilted arch? It was subject to a great deal of controversy. I used to talk to students about the progress from that through the Sickle Bridge in Manchester to the winking eye in Newcastle/Gateshead but this imitation in Exeter is wrong in so many ways.

Even from here the deck looks heavy for what it appears to have to do. And doesn’t that arch go to a strange place?

From the other side there begin to be questions, like why is the arch on the wrong side of the curve.

And those connections (and the “arch” for that matter) look a bit sketchy.

But when you get to the end of the arch, all is revealed, or perhaps “nothing” is revealed.

The arch is mere decoration.

The close boarded fence is a later addition, presumably because the neighbours were not happy with the school kids walking above their hedge twice a day.

I think that the security gates were also an afterthought. You can see the original handrail behind the timber here too.

And this all manages to look a tangled mess.

And finally, the whole thing is painted white, which is fine if you are going to wash it once a month and repaint once a year. The rust stains here are a sign of serious trouble to come.