Regarding the defining the sections in the ETABS

[Yashu Yashu]

Hi I'm analysing a truss having back to back ISMC sections with spacing of 100mm.
I tried modelling using two ways as follows;

Method-1: Defined by choosing the Section Shape as "Steel Double Channel" in the Frame section definer.

Method-2: Defined using the "Section Designer" option in the Frame section definer.

When the members are designed, the model having the sections defined by adopting method-1 passed and the utilization ratios are under 1.

But the model having the sections defined by method-2 (Section Designer) is failed. The utilization ratios exceeded 1.

In both the methods, all the properties are same with out any changes in the engineering properties and member sizes.


Could any one help in resolving the issue. Why the results in both the case are not matching. Which is the correct method to follow.


Thanks.

 

[JoshPlumSE]

We'd have to see where they member capacities are different.

My first guess is that there could be a difference in how the torsional properties are calculated (like torsional warping constants and such) which are used in the beam buckling calculations. Maybe even torsional buckling calculations.