Live load – all you need to know

what is the live load how do you apply it to structures and what units

Structural loads are the basics of structural design. Without defining what loads act on a building or structure, the engineer can’t verify the structural element.

However, there is unfortunately little information online and very few courses at university cover it.

To structurally verify a structure, the engineer needs to consider

  • Wind load
  • Snow load
  • Dead load
  • Seismic load (not in all regions)
  • and the Live Load, which we’ll explain in detail in this blog post.

So in this article, we’ll show, what the live load is, what different units are used and how the live load is applied on structural elements.

Let’s get started.

πŸ’‘ Live load definition

The live load represents variable loads such as weight of people, furnitures, cars, office equipment, etc that can change over time. It’s an approximation for structural engineers to estimate the additional weight (excluding self-weight) that can act on structures due to different room classes.

The values of the live load due to the different categories can be found in EN 1991-1-1 Table 6.2.

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But be careful here! Most National Annex have different values here, and you should always use the values from the National Annex of the country in which you design the structure.

πŸ™‹β€β™€οΈ Examples

Here are some examples of categories of loaded areas which are included in Eurocode:

  • Floors
  • Stairs
  • Balconies
  • Offices
  • Shopping areas
  • Areas with tables
  • Areas with possible physical activities
  • etc.

What is included and what isn’t in the live load can be read in EN 1991-1-1 6.1.

For example, EN 1991-1-1 6.1 (4) notes that “heavy equipment” is not included.

I strongly advise you to take time and read through EN 1991-1-1 to really understand what is included in the live load and what is not.

This article gives only a “quick” overview about the live load.

β†˜οΈ Live load direction

In most cases the live load is applied to a horizontal element like slab, balcony, flat roof, stairs. And in that case the live load can simply be applied vertically, as in the next picture, where a floor slab is supported on 3 edges by walls.

Area Live load is applied perpendicular to the floor slab.
Area Live load is applied perpendicular to the floor slab. Slab supported on 3 edges by walls.

Now, it gets a bit more tricky when we need to apply the live load to an inclined structural member like a rafter roof. We wrote an extensive article about loads on roof structures, and you can check it out here.

But the short version: The live load gets applied to inclined structures, like the dead load.

The load direction is z-axis downwards ⬇️, while the distribution follows the inclination of the roof.

Area Live load on inclined purlin roof.
Area Live load on inclined purlin roof.

πŸ‘©β€πŸ« Unit

The unit of the live load in Europe can be one of the following

  • Area load: $kN/m^2$ = Kilonewton per square meter
  • Line load: $kN/m$ = Kilonewton per meter
  • Point load: $kN$ = Kilonewton

In general, the values of the live load for buildings that are given in EN 1991-1-1 are in $kN/m^2$ or $kN$. Since live loads represent the weight of people, office equipment, etc. in most cases the unit $kN/m^2$ is used and applied to the slabs/floors.

However, when designing beams, line loads ($kN/m$) are used. The line loads are calculated by multiplying the area loads ($kN/m^2$) by the spacing of the beams s.

Area load ($kN/m^2$) applied on slab supported by beams.

As the slab is supported by beams, the line load that acts on the beams is calculated as

$$ Area load [kN/m^2] \cdot s [m] = Line load [kN/m]$$

Line load ($kN/m$) applied on beam.

πŸ’‘

A couple of decades ago, engineers used the unit kg [kilogram] instead of kN.

🀝 Conclusion

Now, that you got an understanding of what the live load is and how it is used, it’s time to look at other loads like

Because there are always multiple loads acting on a structural element. Considering these different loads in the structural design is done by setting up Load Combinations with safety factors.

Once all load cases and combinations are set up, the structural elements can be designed. We have already written a lot of guides on how to design structural elements. Check them out.

I hope that this article helped you understand the live load. In case you still have questions. Let us know in the comments below ✍️.

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