Friend of the blog, Smelter, sent me this picture of a bridge from his work commute saying that he thought I'd find it interesting. He was right. I was intrigued. From what I could see, the bridge was a standard box section railway bridge. The steel, box shaped sides made for a very strong rigid structure perfectly capable of holding the weight of a train. 

But what about those arches? What were they for? They looked like they too were made from steel. The triangular braces would give the arch rigidity, yet keep the structure light in weight. They just didn't seem to be doing anything. Why have arches on the top of a box section? Smelter kindly sent through another picture. I admit that I was none the wiser. If anything, I was a little more puzzled. The arches seemed to have some kind of twist in them. Weird. 

Finally, Smelter let me off the hook sending through this link to the same bridge on Google maps. All became clear. The arches ran across the bridge, not along it. They were there to join the box sections together. The arch would provide clearance for the trains to fit under. 

If you visit the site on Google maps you can have a virtual wander round with street view and see the arches from a few different angle. Thanks Smelter! I really enjoyed that.

Find out more about bridges here.

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Push rods are used to take a movement from one point to another in a mechanism. They generally need to be rigid and relatively strong.

Presented here are three different designs of pushrods that I use in model.

The simplest is the strip of card. This is flexible; actively bendy in fact. It is useful for pushing over very short distances and for only a small amount of force It works well for pulling, in fact if the force being transferred is a pull force this is all you need.

By adding a crease down the middle of the push rod the rigidity of the push rod is increased dramatically. A simple push rod like this is useful even over fairly long distances. It is rigid but doesn't work well if twisted.

The final iteration is to take the strip of card and fold it round into a triangular tube. This is harder to make and bulkier than the other designs but stronger both in the sense that it is the most rigid and that it resists twisting.

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 I've been in my True Love's school today working with year one children making an Eiffel Tower from rolled up newspaper. 

It's been nine years since I left the teaching profession, today reminded me what I used to enjoy about it. The children (6-7 years old) were a delight. They were interested in what we were doing, they solved problem, asked questions and succeeded in making a really impressive tower from a stack of old Guardians.

I even got a chocolate sauce crepe to eat as part of the French theme. What fun!

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