Load trains and short loads

Document history

• 2023-03-30 First version, placeholder.

Terms

Loads are typically organised into:

• Axles
• Bogies
• Vehicles
• Trains (this term is used for abnormal loads on roads as well as rail)

A bogie is a set of axles that are linked. They would typically have a combined suspension system.

A "short" load is an axle or bogie, and excludes any other parts of the load. BD21 and CS454 for road bridge assessment explicitly provide bogie loads for use in masonry bridge assessment. For rail, NR/GN/CIV/025 offers a "short" alternative to the (implicitly) "long" RA1 load model.

Effect of increasing load length

For most masonry bridges, shorter loads are more onerous. That is because, for normal vehicle lengths, additional axles tend to fall either off the bridge, or at a location that will help.

Varying axle widths

Axle widths in a (road) load train may not all be the same. Archie-M loads does not accommodate varying axle width in a single load case. The value of doing so is limited for the reasons discussed above. If you want to check that a combined load is not more onerous, it is possible to position multiple loads on the bridge at once.