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Old 11th August 2014, 09:19 PM   #1
Senior Member
Join Date: Nov 2009
Posts: 27
Default Deflection limits

Hi Tony,
Is there any way you can add to the standard deflection limits for timber elements in eurobeam so there is an option for say L/360 as well as the standard L/150 & L/250
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Old 11th August 2014, 10:48 PM   #2
Tony Bryer
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 827
Default Re: Deflection limits

Thanks for the feedback. L/250 is the default for Eurocode EC5 timber beam deflection where there are brittle finishes (e.g. plaster ceiling under) as against 0.003L (L/333) in BS5268. At first glance it appears that EC5 has substantially relaxed the limit but not so: the BS5268 limit applies to instantaneous deflection, the EC5 limit to long term deflection allowing for creep.

Consider 47x195 C16 floor joists at 400c/s spanning 4m, 0.5kN/m2 dead, 1.5kN/m2 live. Instantaneous deflection is 11.9mm which falls just under the BS5268 0.003L (12mm); under EC5 the long term deflection is 15.3mm, just under L250 (16mm). If you apply an L/360 limit the required size increases to 47x220.

We could add L/360 to the standard options (note that you can type in what ever deflection limit you want: a plain number is taken as mm) but I think that would be more likely to confuse users who are less familiar with EC5 and by using it they would end up with larger member sizes than necessary.
Tony Bryer, Greentram Software Pty Ltd
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