I am designing a piperack modification of a refinery project.
Cantilever beams are considered to support a 24" pipe below the first tier of the structure.
During analysis, it's been fount out that the cantilever of HEB300 loaded with horizontal firction forces is very vulnerable to the weak axis deflection, i.e. in the global X direction of the attached staad input file.
The horizontal drift seems like being calculated by multiplying the angle from the column with the cantilever length.
I did a manual calculation by the formula δ = PL^3/3EI, which put out very small drift as compared to the analysis values by STAAD Pro.
It's figured out the support condition is the key to decide the drift rather than the moment of inertia of the cantilever for the minor axis.
In order to solve out the issue, horizntal ties and bracings are necessary. But the constrution will not be easy and if possilbe I want to make cantilvers only without ties and horizontal bracings as referring to the manual calculation. The beam numbers for the cantiever are as listed next; 2626 2628 2629 2630 2636 2637 2638 2641 2642.
Please, give me your valulabe observations on this issue. Thanks a lot.