How to classify heavy duty and UDL/Point Load TG20


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Jun 29, 2024
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Dear All,

I need help understanding duty class that specifies in TG:20.

Class 4 (Heavy Duty) mentioned that it can have a maximum universal distributed load of 3.0kN/m2. If i convert this to kg it is roughly 300Kg/m2, so if for example i have 2 person (90kg each) and equipment of 100kg. Total of 280KGs (ignoring other criteria such as deadload etc for now)

Does this mean that it falls under Heavy duty? OR do i have to divide 280Kgs by the area to get the UDL?
To determine if your scenario falls under the Heavy Duty (Class 4) category as specified in TG:20, we need to calculate the Uniformly Distributed Load (UDL) for your specific situation. Let's break this down step:
  1. First, you're correct that 3.0 kN/m² is approximately equivalent to 300 kg/m². This is the maximum UDL for Class 4 (Heavy Duty).
  2. You've listed:
    • 2 people at 90 kg each: 180 kg
    • Equipment: 100 kg
    • Total: 280 kg
  3. The key point here is that UDL is measured per square meter. So yes, you need to divide the total weight by the area to get the UDL.
  4. To determine if this falls under Heavy Duty, we need to know the area over which this 280 kg is distributed.
For example:
  • If this 280 kg is spread over 1 m², then the UDL would be 280 kg/m² (or about 2.75 kN/m²), which would indeed fall under Heavy Duty.
  • If it's spread over 2 m², the UDL would be 140 kg/m² (or about 1.37 kN/m²), which would not be Heavy Duty.
So, to answer your question: You do have to divide the 280 kg by the area to get the UDL. The classification depends on this calculation.

To determine the correct duty class, you need to:
  1. Calculate the total weight (which you've done: 280 kg)
  2. Determine the area over which this weight is distributed
  3. Divide the weight by the area to get the UDL
  4. Compare this UDL to the class specifications in TG:20
Also, as you mentioned, for a full assessment, you would need to consider other factors like dead load, impact factors, and any other relevant criteria specified in TG:20.
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