Loads We Design Buildings For
Part #1 of the Structural Loads Series
Hi friends, 👋👋
Ready to kick off a new series? I am very excited about sharing the new series with you, but at the same time enjoying European summer. 🔥🔥
The weather is getting great here in Copenhagen. We’ve had already many days of 20+ degrees, loads of sun, and a few great outdoor events. I am quite hyped about the upcoming European Championship. It’s hosted in Germany and our National team has finally the potential again to get through the group stage. My jersey is ready to be worn.
Are you going to follow the Euros, and let us know in the comments which team you are supporting?
Now, let’s get into the topic of today.
Loads We Design Buildings For
Today, we’ll cover all structural loads I use to design buildings as a structural engineer.
We start with a quick overview of all structural loads that can or must be considered in structural calculations.
From next week, we’ll cover the different types of loads in detail and show how to calculate that type of load step-by-step.
Without further ado, let’s get into it. 🚀🚀
#1 Dead load/ self-weight
The dead load represents the self-weight of all structural and non-structural elements. You usually calculate the dead load with the density of the material, if the value isn’t given by the manufacturer.
For example, the dead load of a concrete slab is calculated as:
So for a reinforced in-situ slab with thickness 250 mm, we’ll get a dead load of:
In structural design, we apply this area load (kN/m2) on the slab. For in-situ slabs, we structural engineers most likely use a Finite Element program to design the slab where we also apply the dead load of the slab as an area load.
#2 Live load
The live load accounts for people, furniture or equipment. So basically variable weights on floors that can change over time.
We find the load values for different room categories in EN 1991-1-1 Table 6.2.
Live loads mostly also act on horizontal elements like slabs as the dead load.
#3 Vertical wind load
The vertical wind load acts on roofs and compared to the other loads acts in most cases perpendicular to the surface of the roof, either towards the surface or away. We also call this pressure or suction.
Be aware that the direction and value of the wind load is dependent on many factors, such as
building height
geometry of structure
location
wind direction
and other factors
Compared to all other loads, the wind load on the roof most likely acts in suction. In that case, you have to make sure that your roof is either heavy (dead load > upward wind load) or that the roof structure is anchored to the supporting structure.
In the following posts of this series, we’ll go more into detail of how to calculate the wind load step-by-step.
#4 Horizontal wind load
Wind loads also act perpendicular to the walls and facades. This leads to horizontal loads ➡️➡️ which – like the vertical loads – have to travel to the foundation.
In structural engineering, this is called stability analysis.
The horizontal wind load is calculated to verify a building’s stability, which is
checking that the horizontal deflection of the building due to the horizontal wind load is less than the criteria
The floor can transfer the loads to the stabilizing walls
The design of stabilizing walls or a different type of bracing system (like tension rods)
#5 Snow load
The snow load is the result of the weight of snow lying on a structure. It’s calculated with formulas given in Standards and Codes. The snow load depends heavily on the location of the building.
In my hometown Kempten, Germany which is located close to the Alps the characteristic value of the snow load is 3.68 kN/m2, while for Copenhagen, where I live and work it’s 1.0 kN/m2.
This makes a lot of sense as there are regions which are much colder and higher up. Therefore, these regions also have a much higher snow load.
Here is a picture of the driveway of my parent’s house. With this much snow, 3.68 kN/m2 seems quite reasonable, right? I don’t think it has ever snowed that much in Denmark.
#6 Earth pressure
The earth pressure needs to be calculated for all underground structures like basement walls, retaining walls, metro stations, tunnels, etc.
It’s the pressure that the soil applies in the lateral (horizontal) direction.
The earth pressure needs to be considered whenever a structure holds back soil. The direction of the earth pressure (load) is mostly calculated as a horizontal load.
#7 Seismic load
The seismic load represents the force generated by earthquakes.
Like the wind load and the earth pressure, it’s also a horizontal load which needs to be considered in the stability calculation of the building.
#8 Imperfections
Imperfections result in additional loads. Let’s consider this:
A point load is applied to a column. However, the column isn’t completely straight, which happened during construction. But the column is instead a bit inclined. This inclination leads to an additional moment at the base support.
The additional moment is calculated as point load * lever arm.
Imperfections are considered in the design of vertical elements like columns, but also in the design of the stabilizing system, where a horizontal imperfection load is added to the seismic load and wind load.
#9 Accidental load
In some designs, accidental loads are considered in the structural design.
For example, in parking garages is an accidental load applied to columns, which represents a car driving against the column.
Conclusion
These are the 9 types of loads that I commonly use in my structural designs. Dead, live, wind and snow load apply to all buildings. While the other types of loads often can be left out.
For example, buildings without a basement don’t have to be verified for earth pressure, and the seismic load is so little for light structures in “earthquake-safe” regions that you can show that the seismic load is smaller than the horizontal wind load, and therefore you will not verify the stability for the seismic load.
This was the #1 episode of the new series about structural loads. As mentioned in the introduction, this was an overview of all loads, and we’ll get into the nerdy calculations from next week on. So be ready for that.
Have a great rest of the week and good luck to the National team you support in their 1st match.
Until next Wednesday. 🙋♂️🙋♂️
Cheers,
Laurin. 😎😎
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