Compression is what keeps an arch together, and seems to be important in holding bridge structures together in the long run, as we have seen in our previous posts on this topic. Now in this post, we will conclude the series.
Architecture that Stands the Test of Time
The fact that the true arch operates in compression means that the increase and decrease of weight on the bridge, the result of moving loads, has little effect on the structure. After all, the bridge is already compressed; the additional weight means simply more compression, as opposed to a wear-inducing bending motion or further tear-inducing stretching. In fact, arches can become stronger over time, simply because they are gradually being compressed tighter and tighter together. It seems as though it is no coincidence that arch bridges are an enduring design; arches are found in nature itself everywhere. The compressive line of force traveling through the arch is neatly and smoothly transferred to solid ground due to the curved shape of the arch.
All bridges do decay in some fashion over time. Yet there are stone arch bridges that were built by the ancient Romans, a couple thousand years ago, that are still in use. Will any of the modern truss, slab, girder, or even suspension bridges be usable several hundred let alone a couple thousand years from now? One cannot help but to think that, with today’s technology and standards, a very good, enduring stone arch bridge could be built that would be far superior to anything else in the way of bridges and would last indefinitely.
Conclusion
We will conclude with pieces taken from a long article written by Walter Sharp, stone arch bridge builder, in 1905:
“…While the various counties in Kansas are considering the bridge problem, I wish to present a few facts about a bridge that is older than any of the colonial furniture now so popular. The arch bridge for beauty has never been equaled. An arch bridge adds beauty to any landscape. The durability and strength of the arch bridge is never questioned. Many arch bridges in Europe built a thousand years ago are still as good as when built and never need repairs….
“The Kansas City Star aptly puts the whole question of stone arch bridges in a nutshell, when it says:
“‘A community that has provided itself with natural stone bridges, or has inherited them from earlier generations — and they have come clear down from Roman times — is as justly proud of them as though they had been fashioned in the making of the world.’
“Walter Sharp.”
Walter Sharp, “Bridge for Douglas Avenue,” The Wichita Eagle, December 31, 1905.
Stone Arch Bridges 