Bridges

Basic notes about bridges ==== Detailed notes about bridges

Other notes about structures ==== All pages about structures

Alphabetical index of bridges and other topics

Please note that all thumbnails have been replaced by blank rectangles,

to reduce bandwidth, because of the heavy usage of these pages.

Introduction to the contents of this web-site

Although the notes in these pages are about structures, they are not about engineering practice. They simply represent an attempt to understand simple structures. The explanations are not intended as a logical and formal set, like a text book, and they use little mathematics, but every possible effort has been made to make them accurate within their limitations.

There is little in these pages about the actual practice of building structures, because that subject is so vast and varied. Building a structure is often a source of difficulty and danger, sometimes from unexpected conditions or phenomena. The engineers must create not only a design that can stand safely for many years, but also efficient means of building it with due regard for safety, cost and the convenience and livelihoods of those affected by the process.

These pages describe standard basic structural components such as arches and beams, struts and ties, often using small and ordinary examples that might be found in many places, rather than large and famous ones.

The structures discussed in these pages are mainly heavy and rigid, but those made by people who travel are very different. For them there are extra criteria, such as portability, ease of assembly and dismantling, and the need to use locally available materials. Many different materials have been used. These dwellings are at one extreme of a spectrum: at the other we find the large pyramids, which are almost completely solid, and immensely heavy. An alternative to portability is to make something that can be left behind because it is so cheap, such as a snow-house. The extreme example is the snow-hole of a mountaineer who has been caught out by bad weather.

Looking at real buildings is of course far more interesting than looking at a site like this, and a visit to any place can be more rewarding if an effort is made to look at buildings, not just as a whole, but in detail: not just in appearance, but in structure. Something with signs of failure may reveal more than something that is in perfect condition. Around the world there is an immense diversity of buildings, creativity being limited only by the laws of physics and the available materials (and local traditions and building regulations).

Many sites about bridges will tell you about the various types, which look very different from each other. And very big bridges can look very different from very small ones. In fact, above a certain size of span, all bridges are suspension bridges: below a certain span, almost all are beams or pipes. Very small insects do not look like very large ones, very small animals do not look like very large ones, very small plants do not look like very large ones, and very small cars do not look like very large ones. The same goes for aircraft and buildings, and many other structures and machines. This tendency was discussed by Galileo Galilei in Dialogues Concerning Two Sciences, Second Day, section 151 onward.

Although many bridges can be classified clearly into types, some cannot, and many buildings or parts of them contain elements that cannot be so neatly classified. In this web-site you can, for example, find out how beams, cables and arches are not as distantly related as they might seem.

Some structures, such as one-storey buildings, have no physical function other than remaining stable under any likely combination of external forces, such as those due to gravity, wind, flood water, earth tremors, and snow. Structures such as bridges and cranes have in addition to deal with the weight of deliberately applied loads. In all cases, the structure has to create exactly the right forces to keep everything in equilibrium. In this site you can find out how this is done, and what happens when the forces are not created quickly enough.

Although most of these pages are about bridges, these structures, however spectacular, are no more typical of canals, railways and roads than pearls, also initiated by unwelcome intrusions, are of oysters.

Basic notes about bridges ==== Detailed notes about bridges

Other notes about structures ==== All pages about structures

Alphabetical index of bridges and other topics