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Old 11th August 2014, 09:19 PM   #1
asutcliff
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Join Date: Nov 2009
Posts: 26
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
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Location: Melbourne, Australia
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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.
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