1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Span tables & CSC Tedds

Discussion in 'Building Regulations and Planning Permission' started by frank999, 3 Oct 2012.

  1. frank999

    frank999

    Joined:
    11 Feb 2009
    Messages:
    440
    Thanks Received:
    3
    Location:
    London
    Country:
    United Kingdom
    I have a calculation for a flat roof joist run on CSC Tedds:

    50x175mm
    C24
    400mm centres
    UDL: 0.75kN/m2
    Dead Load 1.00kN/m2
    3900mm span

    Trada Span tables:
    Table 2.36
    Access only for
    cleaning and maintenance
    Imposed load 0.75 kN/m2;
    C24
    Dead Load [kN/m2 ]: More than 0.75 but not more than 1.00
    47x170mm
    This is giving me a max span of only 3690mm.

    Any reason why the Software (CSC Tedds) is giving a greater span ?
     
  2. Sponsored Links
  3. jeds

    jeds

    Joined:
    16 Apr 2004
    Messages:
    4,085
    Thanks Received:
    526
    Country:
    United Kingdom
    It's your span table that's wrong. The current table gives span of 3850. Maybe you are using the old table?
     
  4. tony1851

    tony1851

    Joined:
    23 Feb 2012
    Messages:
    9,388
    Thanks Received:
    1,402
    Location:
    Manchester
    Country:
    United Kingdom
    Neither is 'wrong'in the strict sense of the word. It depends on how much deflection is allowed for in the tables and calcs.
    Whoever wrote the calculation software obviously allowed for more deflection than those who prepared the tables.
     
  5. frank999

    frank999

    Joined:
    11 Feb 2009
    Messages:
    440
    Thanks Received:
    3
    Location:
    London
    Country:
    United Kingdom
    Your right, it could be an old table.

    I assume tables would err more on the side of caution as they are more general, the software can give a greater span as you can be more specific ie such as with deflection ...
     
  6. jeds

    jeds

    Joined:
    16 Apr 2004
    Messages:
    4,085
    Thanks Received:
    526
    Country:
    United Kingdom
    The newer tables are more relaxed compared to the old ones. The new Eurocodes are the same. I'm finding calculations based on similar loads coming out a serial size smaller in some cases. Incidentally, the standard deflection used in tables is 0.003xspan but not more than 14mm. All the softwares I know use the same standard.
     
    • Thanks Thanks x 1
  7. RonnyRaygun

    RonnyRaygun

    Joined:
    4 Apr 2008
    Messages:
    1,672
    Thanks Received:
    239
    Location:
    Hertfordshire
    Country:
    United Kingdom
    I thought I could answer this one with an Excel calc...bearing in mind TEDDS should give exactly the same answer.

    So I set up the spreadsheet, and through trial and error found the maximum span governed by deflection, given the info above.

    I keep getting 4170mm...

    Now this seems long, so I'm wondering if I've made a mistake somewhere...can't see one though...

    I did go to a wedding yesterday though and am feeling a bit groggy this afternoon :rolleyes:

    *Edit* Was using 175mm rather than 170mm as depth, but still getting 4050mm as maximum span...
     
  8. baxiengineer

    baxiengineer

    Joined:
    26 Mar 2005
    Messages:
    25
    Thanks Received:
    7
    Country:
    United Kingdom
    yep 7x2 in old money that will be half the span plus one inch gives you the 7
    anything over 14ft goes to 3 inch timber
     
  9. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
  10. Sponsored Links
Loading...

Share This Page