What is an alternative load path?
An alternative load path (Dutch: tweede draagweg) is a structural design measure that lets loads find another route to the foundations when part of the structure fails. If a column is knocked out by a vehicle impact or an explosion, or a tension rod snaps, other members take over the load. Local damage stays local, and the building does not fold up like a house of cards.
Why is it needed?
A structure that relies on a single load path is vulnerable to progressive collapse: the failure of one member drags the rest down with it. A well-known example is Ronan Point in London (1968), where a gas explosion blew out an external wall panel and an entire corner of the tower block collapsed over many storeys. Since then robustness has been a standard part of structural design.
In Europe, accidental actions such as impact and explosion, and strategies for robust structures, are covered by EN 1991-1-7. How demanding the requirements are depends on the consequence class of the building.
Application
- Continuous reinforcement and ties: connecting floors and beams so they can hang from the rest of the structure if a support is lost.
- Multiple tension rods or cables: so that one breaking does not lead to failure.
- Key elements: designing critical columns or walls strong enough to resist an accidental load.
- Impact protection: guarding columns in car parks or next to roads.
Related safety measures
An alternative load path is related to other measures that cope with an emergency, such as a shear bolt or wired glass. The difference is that an alternative load path carries load itself.
Practical tips
- Renovating? Check the load paths: removing a wall or cutting through a floor can interrupt a load path you cannot see. Always have a structural engineer assess it.
- Ask about the consequence class: it determines which robustness measures your project needs.
Related terms
- Structural stability
- Structural engineer
- Consequence class
- Tension rod
- Shear bolt
- Column
- Reinforced concrete
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