Timber Member Design Check

[simjack]

Hi,

I am carrying an assessment of a timber truss. 

I assigned each member a "Member type". For example, member 8 is a "top Chord" member type. The effective length for buckling above major axis has been defined to coincide with points where the member meets adjoining elements and for buckling along minor axis every 400mm. I tried to define bracing for "lateral buckling" at every 400mm as well, however, when I run the analysis the effective length comes as 7.09m Do you know why is that?

Also I was wondering, does the software automatically set up the material parameters for an appropriate load duration? And the deflection values, are those final deflection values including creep? 

I have attached the model and was wondering whether you could have a look and advise on the issue or point out any other issues connected to the model. 

Thank you

[Simau]

@simjack

I didn't see any problem in my model (here attached)

Even without LTB top chords are not correct.

[simjack]

any chance you could re-submit in lower (2017) version?

[Simau]

@simjack

Here it is

[simjack]

Thank you for your help Simau.

Your model appears to work for member 8 but if you have a look at member 9 who is assigned exactly the same parameters as member 8. The buckling is not even being checked ? 

I find it hard to believe that it takes this long to solve it really. i dont understand what Im missing here.

[Simau]

@simjack

Both structure and loads are not symmetric .
Buckling may not be preponderant for the bar 9.

[simjack]

I dont think it would be this case. 

[Simau]

[Simau]

Will take a look later

[Simau]

@simjack

A new model with top chords splited.

Only 3 parts don't work and as you see they are not symetrical.

Model attached

[simjack]

Hi Simau,

Thank you for your help Simau. However, by splitting the bars, you changed the bending stresses in the members. I'd prefer to get the result I'd expect by running the analysis rather than simply amending the structure to get what could potentially be right. 

@Artur.Kosakowski Could you please have a quick look at the attached model and let me know what you think. Why is the lateral buckling length not taken as 400mm although thats what I defined it to be for bottom and top chord? I recon I followed the steps you recommend in Webinar 3.

Is the serviceability deflection taking creep into an account?

[Simau · Accepted solution]

@simjack

[simjack]

@Artur.Kosakowski Can you please have a look. I am honestly getting a little desperate here now. 

[Artur.Kosakowski]

Hi @simjack

Try to define the internal LTB bracings using the relative values (e.g. 0.2L, 0.4L etc.) rather than the absolute ones (such as 1.2m; 1.4m etc.). 

The influence of creep on deflection is disregarded.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[simjack]

OK. Thanks for clarifying the deflection. Is there a way to amend Ksys factor?

[Artur.Kosakowski]

Hi @simjack

In this way:

 

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Artur.Kosakowski]

Hi @simjack

@Artur.Kosakowski Could you please have a quick look at the attached model and let me know what you think. Why is the lateral buckling length not taken as 400mm although thats what I defined it to be for bottom and top chord? I recon I followed the steps you recommend in Webinar 3.

This was actually perfectly answered by @Simau (see message 31). You cannot define the entire bar length as 0.4m and at the same time define restrains to be spaced each 40 cm for the bar length as it is in reality.

In general you should not change the default values in these fields which was part of the webinar.