In 2002, looking across Cheltenham from the nearby Leckhampton Hill, you could see a new structure, unlike anything else in view.  It looks like a white curve rising and falling among the buildings.  From the town itself, it is not easy to see unless you are quite close to it.

What is it?  Here is a picture.  The elegant white structure is Honeybourne foot-bridge.  Let’s see what we can learn from it.

The bridge comprises two trussed tubular arches linked in a few places by cross-members which are also tubular.  The consistent use of tubular members creates a unity of design, and in directional illumination the curves provide a soft gradation of brightness.  Shadows on the bridge are often curved also.  The structure will be easy to paint when the need arises.  The arch is narrower at the crown than at the springing, and so the hangers are not vertical.  But all the hangers on each side are parallel, which greatly benefits the appearance.  Lighting has been integrated neatly into alternate fence supports, eliminating the need for obtrusive lamp-posts on the bridge.  From most directions, the bridge looks reasonably neat and simple to understand.

All four chords end in pinned attachments to the abutments, allowing some degree of movement under changing loads and temperature.

There is something a little strange about these abutments.  Look at the pictures at left.  The thrust line of the lower chord dives safely into the ground, but that of the upper chord emerges into the air not far behind the attachment.  Does this mean that the upper chord in fact carries little or no thrust?  Or is there within the abutment a means of containing the thrust and diverting it to a new direction?  Can you think of any ways of achieving this?  

It is often the case that once a structure is complete, it is not possible for anyone but an engineer to "reverse engineer" it mentally to work out what happens.  It may in fact be impossible for anyone to work out what happens.  It is even possible that the designer does not always fully understand every detail.  This must have occurred frequently in earlier times when theoretical knowledge was less complete than it is now.

Even today, some things are created empirically, and even today, surprises are sprung, notably the pedestrian assisted oscillations of the London Millennium bridge.