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16th November 2011, 02:47 PM  #1 
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Basic Loadings for Floor Joists  Help!
Help Please,
Having just installed the UK superbeam software to try to calculate the flitch beam equivalent of timber joists, i can't even seem to find how to input the basic loads for floor joists. The default seems to be for kn/m run whilst the info i have to go on (from Building Regulations Part A 1992 span tables) are 0.5kn/sq.m dead load (excluding self weight of beam) plus maximum imposed load of 1.5kn/sq.m with the joists at 400mm centres? Can anyone please advise how and where i can enter this data in the manner above ? 
16th November 2011, 09:45 PM  #2 
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Re: Basic Loadings for Floor Joists  Help!
You need to distinguish between kilogram (kg) which is a unit of mass and kilonewton (kN) which is a unit of force. Weights of materials and imposed loads are generally given in kg and kg/m2; our structural programs require loads to be entered in kN. The conversion from one to the other is 1kg=9.81N, for structural engineering purposes generally taken as 10. Thus 50kg/m2 translates to 500N/m2 or 0.5kN/m2. If you want the load on a single joist with joists spaced at 400mm centres, multiply the load by 0.4.
More on this at http://en.wikipedia.org/wiki/Mass_ve...orces_on_Earth If you're using any of our programs it is vital that you do fully understand this, otherwise your calculations will be out by a factor of ten (as has happened elsewhere in the past).
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Tony Bryer, Greentram Software Pty Ltd 
17th November 2011, 10:02 AM  #3 
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Re: Basic Loadings for Floor Joists  Help!
thanks for the reply, i understand the difference between kg and Kn, am i right in saying that you cannot enter kn/sq.m loads, i.e. you have no option other than to enter loads in kn per m. run?
and in order to do that i need to multiply my total load (per sq. m) by the frequncy of spacing, thus 0.5kn/sq.m. + 1.5kn/sq.m. (dead + imposed load) x 0.4 (400mm joist centres) = 0.8kn/m Though i have to admit with all the loadings provided in kn/sq.m it would be good if we did n't have to convert before entering data as i wanted to look at truss rafter loadings as well (which are all in kn/sq.m!) 
17th November 2011, 09:03 PM  #4  
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Re: Basic Loadings for Floor Joists  Help!
Quote:
Quote:
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Tony Bryer, Greentram Software Pty Ltd 

29th November 2011, 07:28 PM  #5 
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Re: Basic Loadings for Floor Joists  Help!
I do quite a few loft conversions so I am often designing floor joists from first principles. I have found it easiest to simply work with a 1m strip of floor.
Floor load is then 2kN/sqm over 1m width or 2kN/m Any purlin wall loads are derived from a 1m strip of roof and the reactions yield loads per metre for any supporting beam. All that needs to be done is to set the required depth of section and "?" for width. I just then pick a suitable combination of spacing and width to give me the width of timber required per metre. This allows me to juggle options to give optimum solutions. Hope this helps 
5th December 2011, 10:37 AM  #6  
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Re: Basic Loadings for Floor Joists  Help!
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For anyone reading this who hasn't quite got it, you enter the floor and any other loads for a 1m bay, choose your joist depth and put ? in the width field. Suppose the required width comes back as 175  this translates to 175/47 = 3.72 joists per metre and the maximum joist spacing is therefore 1000/3.72 = 269mm. You probably need to add a note to the calculations or put (consider 1m bay) or similar in the location field to make it clear to a checking engineer what you've done.
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Tony Bryer, Greentram Software Pty Ltd 

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