Span Ranges and Span to Depth Ratios for Highway Bridges

One of the most common constraints in the IStructE exam is spanning a known distance with limited construction depth (e.g. due to headroom clearance requirements underneath the structure), so the span and span to depth ratio are two of the key pieces of information you can use to identify a suitable superstructure type.

The following cheat sheet lists different types of superstructure for highway bridges, and the range of spans where they are suitable. Dark blue lines indicate the most economical span range; light blue indicates spans of this length are possible but may be less economical.

The graphs are annotated with "span to depth ratios" and other key layout information.

Note that the graph is for highway bridges only - span ranges and span to depth ratios are different for footbridges and railway bridges.

This following sources of information were used to produce the graphs:

1. Jensen, C (2008) 'ICE Manual of Bridge Engineering'
2. Davison, B (2003) 'Steel Designer's Manual', 6th Ed
3. McFerich (2019) 'Encyclopaedia of British Bridges', 2nd Ed.
4. The Structural Engineer / April 1974 / No. 4 / Volume 52
5. Advice from senior colleagues!