Hello friends, 🙋♂️🙋♂️
Hope you are fine. Last week, we covered the first structural load that we use to design buildings - the dead load. Today, we’ll check out the live load. We cover:
what the live load is
examples of the live load
load values of the live load due to different categories
the load direction (how you apply the live load to static systems
So let’s get into it. 🚀🚀
What Is The Live Load?
The live load represents variable loads such as the weight of people, furniture, cars, and office equipment that can change, moved or removed 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/categories.
The values for the live load are defined by standards such as Eurocode. There are values defined in the general Eurocode EN 1991-1-1, but most countries define these values differently in their National Annexes.
We’ll summarize these live load values in a later section. ⬇️⬇️
Examples of the Live Load
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. As always, this newsletter gives only an overview over the topic. Structural engineering and its problems are so diverse that it’s impossible to cover every and mention every detail and design situation.
Values of The Live Load According To EN 1991-1-1
You can find the load values of the different categories for residential, office, and other types of buildings in the 4 tables below. Note, that they are given in ranges. Usually, every country defines the live load values in their National Annex.
Live Load Direction
In most cases, the live load is applied to a horizontal element like a slab, balcony, flat roof or stairs. 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.
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. Do you still remember how to apply the dead load on inclined members from last week’s episode?
The load direction is z-axis downwards ⬇️, while the distribution follows the inclination of the roof.
The Live Load Applied To Beams
In general, the values of the live load for buildings that are given in EN 1991-1-1 are in 𝑘𝑁/𝑚2 or 𝑘𝑁 (we have summarized them above). Since live loads represent the weight of people, office equipment, etc. in most cases the unit 𝑘𝑁/𝑚2 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/𝑚2) by the spacing of the beams s.
As the slab is supported by beams, the line load that acts on the beams is calculated as
This line load can then be applied to the beam. With it, the internal forces can be calculated, and then you can design the element.
Conclusion
So far, we covered the dead load in episode #2 and the live load today in episode #3. In the next weeks, we’ll check out the wind load in detail. This takes a few episodes as it’s more complicated to calculate and there are many special cases that we want to cover.
If you missed episode #1 or #2 of this new series, then you can find all previous posts → here ←.
Have a great rest of the week.
Until next Wednesday. 🙋♂️🙋♂️
Cheers,
Laurin. 😎😎
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