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## Robot Structural Analysis

Active Member
Posts: 9
Registered: ‎02-23-2010

# Timber Tapered Beam

596 Views, 4 Replies
06-29-2012 02:10 AM

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?

Active Member
Posts: 9
Registered: ‎02-23-2010

# Re: Timber Tapered Beam

06-29-2012 02:45 AM in reply to: cairoliangelo

I forgot the file ....

Product Support
Posts: 5,105
Registered: ‎12-17-2010

# Re: Timber Tapered Beam

07-02-2012 03:27 AM in reply to: cairoliangelo

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
Active Member
Posts: 9
Registered: ‎02-23-2010

# Re: Timber Tapered Beam

07-02-2012 08:15 AM in reply to: Artur.Kosakowski

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).

Best regards

Angelo

Product Support
Posts: 5,105
Registered: ‎12-17-2010

# Re: Timber Tapered Beam

07-03-2012 12:06 AM in reply to: cairoliangelo

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