triangle steel truss

[shijie0411]

Hi everybody,
I'm new user of Etabs, I built a triangle steel truss model using Etabs, top chord and bottom chord were modeled as continuous member, inside webs are pinned to top and bottom chord, the calculated internal forces seem to be right, but in member design, the program consider the length for bottom chord as the whole length between the two supports for the truss, not consider the design length as between the connections with web members, which is not right and resulted in giving a large member size for the bottom chord. Anyone has any idea why this is about and how to resolve this problem?
Thank you.

 

[structSU10]

All programs read an unbraced length as the member length unless specifically defined. If you model the member as two member between web members it will be designed correctly. You can still maintain fixity between the two elements too.

 

[shijie0411]

Thank you very much. I will try it that way. But I found under steel frame design, there is one command setting bracing for the member, I also tried this, but making no difference for design result, for my understanding it refers to bracing out of plan, is it right? when we use this?

 

[structSU10]

You should be able to assign bracing as you described. Usually it is defined either in the strong or weak axis of the member.

 

[shijie0411]

Thanks a lot!