Advertising sign structures seem to becoming more interesting than the adverts they display and recently Sir Albert Bore, the leader of Birmingham City Council, opened the striking Millennium arches in Birmingham.

The arches, which act as advertising signs, are formed from 457mm diameter tubes which were curved to the elliptical profiles by Angle Ring.

Bending any large diameter tube to an ellipse is not without its difficulties, the 457mm diameter required for the arches needed to be curved to a smooth elliptical profile as the steelwork is not clad in any form.

A simple way to solve the problem of the ellipse is to bend short segments to calculated single radii and join into the profile required, in the same way a simple ellipse is drawn using a compass. However, as the tube increases in diameter, any degree of bend will introduce an amount of ovality . This ovality  will vary from one piece to the next as each portion of tube is curved to a different radius and the deformation increases as radii decreases. This in turn results in a noticeable blend between the bends where the tube profile alters.

To eliminate this, the sections are curved using hot bending methods which minimises the ovality to within easily acceptable tolerances.

The bar itself is also curved to a more complex ellipse consisting of many radii giving a gradually changing bend. This process is done within a single bar length where possible negating welds and allowing the material to naturally smooth, which also gives a much more pleasing profile for the eye.

The arches are just one example of a number of modern advertising signs using steel curved by Angle Ring. Previous work includes the Wandsworth and Old Street roundabouts.

Structural engineers: Stewart & Harris
Original Design by Score Outdoor Advertising
Photographer - Paul Middleton of Angle Ring