Steel stringer support at top

[buleeek2]

Hello,

I am looking for opinions about the proper support condition at the top of the stringer. I ran 3 analyses of the same typical steel stringer: HSS tube with 6" bent at the top and bottom. The bottom has a base plate with 4 anchor bolts and a foundation. The top of the stringer will most likely be attached to the LVL beam. Please take a look at the attached pdf and let me know your opinion on which model you consider the most accurate. I am trying not to go with "A" (pin connection) as it yields uplift and huge thrust. Analysis B is not accurate, as the wood beam provides some lateral stability and horizontal reaction. Is "C" the most accurate?

Thank you,

 

[JAE]

I would presume that the LVL is integrated into the upper floor (diaphragm) such that there is lateral resistance to movement - thus your Option B with a roller isn't accurate and you are rightly doubtful as to its accuracy....but for design of the stringer itself, I would be OK with using this one.

A pure infinitely fixed support at the top (horizontally) isn't possible either so Option A is not very accurate as there will be some "give" in the floor diaphragm.

I don't believe that your connection to the LVL will really produce any meaningful moment rigidity so that tiny bit of negative moment at the top of your stringer probably isn't something to worry about. The LVL probably has relatively tiny stiffness rotationally as the wood is much softer than the steel and the connections at the LVL ends probably don't produce much torsional resistance either.