Greentram Software Support Forums  

Go Back   Greentram Software Support Forums > SuperBeam > Support

Support Technical and other questions related to the use of SuperBeam

Reply
 
Thread Tools Display Modes
Old 16th November 2011, 02:47 PM   #1
mannkumar
Member
 
Join Date: Nov 2011
Posts: 2
Default 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 ?
mannkumar is offline   Reply With Quote
Old 16th November 2011, 09:45 PM   #2
Tony Bryer
Administrator
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default 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).
__________________
Tony Bryer, Greentram Software Pty Ltd
Tony Bryer is offline   Reply With Quote
Old 17th November 2011, 10:02 AM   #3
mannkumar
Member
 
Join Date: Nov 2011
Posts: 2
Default 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!)
mannkumar is offline   Reply With Quote
Old 17th November 2011, 09:03 PM   #4
Tony Bryer
Administrator
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default Re: Basic Loadings for Floor Joists - Help!

Quote:
Originally Posted by mannkumar View Post
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
Yes, this is right assuming you are checking a single joist. When you enter loads like this, use the option to enter them as expressions as it makes checking easier -for example enter Floor dead as 0.5 x 0.4 (or 0.5 * 0.4) rather than 0.2.

Quote:
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!)
It has to be converted at some stage: we've used kN for load entry for 22 years so aren't likely to change now!
__________________
Tony Bryer, Greentram Software Pty Ltd
Tony Bryer is offline   Reply With Quote
Old 29th November 2011, 07:28 PM   #5
steve ladner
Member
 
Join Date: Aug 2008
Location: southend
Posts: 9
Default 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
steve ladner is offline   Reply With Quote
Old 5th December 2011, 10:37 AM   #6
Tony Bryer
Administrator
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default Re: Basic Loadings for Floor Joists - Help!

Quote:
Originally Posted by steve ladner View Post
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
Yes, this is how I used to do it 25 years ago when I was designing loft conversions by the dozen. Invariably ceiling height was a major issue (2.3m min across half the room rule in force then) so the floor joist depth was fixed (often 125mm when 150 or more was desirable) and it was just a question as to how many you had to throw in. As you say, work on a 1m bay and get an overall joist width, and this then gives you the spacing.

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.
__________________
Tony Bryer, Greentram Software Pty Ltd
Tony Bryer is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



All times are GMT. The time now is 01:30 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2011 Greentram Software Pty Ltd, Melbourne, Australia