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Timber Tapered Beam

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Message 1 of 9
cairoliangelo
1708 Views, 8 Replies

Timber Tapered Beam

Hi,

 

I can’t understand the results of the calculation on a timber tapered beam.

 

In the attached example, the cross section is a rectangular beam 26x45cm. The additional checks are enabled, yet the section in which the verification is done is the one at minimal height (at the beginning of the beam: W=8775,00 cm3), but with the maximum bending moment (Md=359,60kNm).

 

Why is that?

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8 REPLIES 8
Message 2 of 9

I forgot the file ....

Message 3 of 9

These additional parameters are intended for switching on additional verifications that are requested for the profile types shown on the pictures. They  do not change the section you defined in the model (so the basic checks are done for in your case for the cross section with the constant height) but result in additional checks being done (see the attached picture).

 

In your example you should define the beam as two tapered bars with the 'tapered' timber design label assigned.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 4 of 9

Artur, thanks for your answer.

But I do not still understand why the Sig_m,d in the example is 44,59MPa

I Think that is from this calculation: Sig_m,d=kl * Md / W = 1,09 * 359,690 / 8,775 = 44,7MPa very close at the result 44,59MPa.

But in the formula 6.41 of EC5, W is calculated in the apex zone; thus W must be calculated with the max height (0,72m) and the result of the calculation is Sig_m,d=kl * Md / W = 1,09 * 359,690 / 22,464 = 17,45MPa very far from 44,7MPa.

In the same way I think that the calculation of Sig_t,90,d is overestimated: it is the calculation of the tensile stress perpendicular to grain and this tensile stress must be only in the max height zone (0,72m).

I kindly ask you to send me your opinion about this matter.

Best regards

Angelo

Message 5 of 9

Angelo,

 

As I wrote in my previous answer the selection of a beam shape you make in the EC5 parameters assigned to a bar does not change its cross section from uniform height to the tapered one. Its aim is to switch on additional verifications that are not needed for a section with the constant height. If you look at the picture I attached previously you can see that the correct approach is to model the tapered beam in the structure (member 4 created from bars 2 and 3) and then run its verification with additional tapered beam verification switched on. If you look at the verification dialog I attached you can see that the value of stresses in the middle of the beam (marked with the orange rectangle)is calculated for the height in this location rather than the value at the beginning of the beam.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

 



Artur Kosakowski
Message 6 of 9
hv205
in reply to: Artur.Kosakowski

Please clarify how to turn on additional verification - I can't find the dialog box shown in your screenshot. 

Message 7 of 9
Artur.Kosakowski
in reply to: hv205

Here you are:

 

EC5 additional bar type parameters.PNG

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 8 of 9
hv205
in reply to: Artur.Kosakowski

Thanks. Does this apply only to timber beams or is there an equivalent for steel beams? 

Message 9 of 9
Artur.Kosakowski
in reply to: hv205

Applies to timber design only. 

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski

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