Design of floor joists in a domestic building

In summary, the conversation discusses the design of floor joists for a domestic building with a span of 3.0m between walls. The construction of the floor includes 18mm timber boards, joists, and 15mm overall plasterboard with a skim coat. The joists are 50mm wide and at 450mm centres, with a permissible stress of 5.3N/mm(squared) and an elastic modulus of 8000N/mm(squared) for the timber. The deflection must be limited at 0.3% of the span. The individual seeking help clarifies that this is for a college assignment and they are struggling with the calculations. The conversation also mentions the need for a licensed engineer familiar
  • #1
john paul jr
2
0
Could i have some help with the following:

Design, floor joists in a domestic building to span between walls 3.0m apart.

the construction of the floor is
18mm timber boards
joists
15mm overall plasterboard + skim coat

The joists are 50mm wide and at 450mm centres
The permissible stress in the timber is 5.3N/mm(squared) and the elstic modulus of the timber is 8000N/mm(squared)
the deflection must be limited at 0.3% of the span.
 
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  • #2
john paul jr said:
Could i have some help with the following:

Design, floor joists in a domestic building to span between walls 3.0m apart.

the construction of the floor is
18mm timber boards
joists
15mm overall plasterboard + skim coat

The joists are 50mm wide and at 450mm centres
The permissible stress in the timber is 5.3N/mm(squared) and the elstic modulus of the timber is 8000N/mm(squared)
the deflection must be limited at 0.3% of the span.

What is your background? What city is this in? What are the local codes regarding this kind of construction? You need a licensed engineer to make those calculations for you -- one who is familiar with your municipality's building codes and inspectors.
 
  • #3
Is this homework? If not, there's not much of a chance for getting an accurate result without knowing local building codes.
 
  • #4
Even if we had a PE structural engineer as a member or on staff, we wouldn't condone giving such advice since we can't be sure this isn't a code violation (a homeowner trying to do his own structural engineering).
 
  • #5
Thanks for getting back to me this is actually a college assignment that I've been stuck on for quite a while that i needed help on for designing the floor joists.
 
  • #6
Ok so is a college assignment. Start off by showing your work, so we can know with what you are having problems.
 
  • #7
john paul jr: Do you have the density of the timber boards, and of the joist material? Do you have the density of plasterboard? Do you have the floor applied live load per unit area?
 

1. What is the purpose of floor joists in a domestic building?

Floor joists are an essential structural element in a domestic building that provide support for the flooring and distribute the weight of the building to the foundation. They also help to prevent the floors from sagging or bouncing.

2. How are floor joists sized and spaced?

The size and spacing of floor joists in a domestic building are determined by building codes and standards. Factors such as the span of the joists, the type of flooring, and the weight it will need to support are taken into consideration when determining the appropriate size and spacing.

3. What materials are commonly used for floor joists in a domestic building?

The most commonly used materials for floor joists in domestic buildings are wood, steel, and engineered wood products. Wood is typically used for smaller, lighter buildings, while steel is often used for larger or commercial buildings. Engineered wood products, such as laminated veneer lumber, are a popular alternative to traditional solid wood joists.

4. How are floor joists connected to the rest of the building's structure?

Floor joists are typically connected to the building's walls via joist hangers or ledger boards. Joist hangers are metal brackets that are attached to the walls and hold the ends of the joists in place. Ledger boards are horizontal beams that are fastened to the walls and provide support for the ends of the joists.

5. Can floor joists be modified or replaced if needed?

In most cases, floor joists can be modified or replaced if needed. However, it is important to consult a structural engineer or building professional before making any modifications to ensure that the structural integrity of the building is not compromised. Replacing floor joists may also require obtaining a building permit and following specific building codes and regulations.

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