There is no facility in STAAD to specify a beam with 2 webs, except as a rectangular tube.
We often find users trying to approximate a non-standard or built-up section to a "General" section type through a user table in STAAD. But STAAD designs a User Table General section using the rules applicable for a doubly-symmetric I-shaped (wide flange) section.
If that is what you have done too, the program will not be able to recognize the true shape of the section.
The code checks that STAAD performs on any member are done at a total of 13 section locations along the member span - start, end, and 11 intermediate. At each of those locations, it checks to see which flange is under compression for the moment MZ (MY is used if SET Z UP is specified). The flange that is on the positive side of the local Z axis is in tension when MZ is positive, and in compression when MZ is negative (vice versa for the other flange). After the flange that is in compression is established, Iyc is calculated for that flange.
We often find users trying to approximate a non-standard or built-up section to a "General" section type through a user table in STAAD. But STAAD designs a User Table General section using the rules applicable for a doubly-symmetric I-shaped (wide flange) section.
If that is what you have done too, the program will not be able to recognize the true shape of the section.
The code checks that STAAD performs on any member are done at a total of 13 section locations along the member span - start, end, and 11 intermediate. At each of those locations, it checks to see which flange is under compression for the moment MZ (MY is used if SET Z UP is specified). The flange that is on the positive side of the local Z axis is in tension when MZ is positive, and in compression when MZ is negative (vice versa for the other flange). After the flange that is in compression is established, Iyc is calculated for that flange.