Arches are structures made using different kinds of curves. They are very important in engineering and architecture, for example in bridges, tunnels, roofs, doorways and windows. They spread weight to either side.
Semi-circular arches are the simplest. They were used especially in Norman architecture, for example in the famous doorway at Strata Florida Abbey, Ceredigion. You can see that the arch is half of a circle.
When less than half of the circle is used, the arch is called ‘segmental’. An example is Llanrwst Bridge near Conwy. You can see that the arches are nearly semi-circular but if you look at the reflection you can see that it is quite squashed.
A rope bridge makes a shape like an arch but the other way up. An arch made to the same shape is called a catenary arch. This print shows the catenary shape in a rope bridge to the lighthouse at Holyhead.
Another catenary curve is the chain that supports the Menai suspension bridge designed by Thomas Telford.
The North Wales architect Herbert Luck North designed graceful rooflines using segments from ellipses, drawn out at either end.
Thomas Telford designed bridges across the Llangollen Canal with elliptical arches. He needed the bridge to be wide enough for the canal but easy for vehicles to cross. A semi-circular arch would have been too high or too narrow. A wider elliptical arch was perfect.
Possible to visit:
- Look at buildings and bridges in your area to decide what kind of arches have been used.