Inclined Steel Frame

I will call the steel support an inclined post, is this member your concern? Do you have eccentric lateral load, I don't quite understand the rotation and potential moment in the "column (which one, steel, concrete)? Yes, you need to explain better.

I did a sketch. I hope it explains better.
My concern is the plate at the top of the post. would it carry flexural stresses? knowing that the steel post is modeled to be free at top.
In case the plate carries flextural stresses and failed accordingly, would that affect the stability of the steel frame?

Thanks,

If the column is stable without the connection. Why provide the connection at all?

Agent666
It was provided to prevent movement in the transverse direction

The steel post is not free after attached to the concrete roof. Other than self weight of the concrete, every load on the roof will be felt by the steel post through the link (looks like two built up tees). However, if the concrete structure was designed as cantilever, then the failure of the link alone will have minor, or no affect, on the steel framing, but the lateral load resisting capacity is lost. Can the concrete structure resist lateral load without the steel post?

retired13
The concrete structure is existing structure.
The steel post is not intended to support the concrete structure.

My concern is the lack of horizontal displacement restrain in direction shown on sketch below. Wasn't that your intention?

OP said:

It was provided to prevent movement in the transverse direction

Click to expand...

I would have thought that the plate at the top would be rotated 90 degrees.


Dik

retired13
my concern is that the failure of the link due to bending would affect the stability of the steel frame as a whole

1) I mostly like what you've done here and feel that your detailing is quite reasonable.

2) I think that the axially slotted holes are prudent to keep the posts from absorbing axial loads when the the concrete structure above deflects, vertically or laterally.

3) We usually don't rely on slotted holes to accommodate movement because they tend to be prone to binding up. If this is indoors, however, I suspect that you'll be okay on this front. You have little load transverse to the slots and the connection won't be in a corrosive environment.

OP said:

Or .. the column would not induce loads on the connection because it's still stable even if it's free?

Click to expand...

4) I don't agree with that as an argument to justify the absence of force development on the connection.

OP said:

my concern is that the failure of the link due to bending would affect the stability of the steel frame as a whole

Click to expand...

5) I see what you're getting at but I don't feel that you need to be concerned. Given the drift that you can reasonably expect in the existing building, you'll not induce enough angular change at the top of the column to induce significant moments in the connection plates. You may not even induce enough angular change to use up the rotation capability that may or may not be present as a result of the slight oversize in the bolt holes.

OP said:

my concern is that the failure of the link due to bending would affect the stability of the steel frame as a whole

Click to expand...

As the concrete structure was designed for self-support, and the steel posts are attached for the sole purpose of holding the steel frame in place, where the load/force, that could cause bending in the link, may come from? Are you in an earthquake active zone, if so, did you checked the frame with the top of the steel posts set free? The result of this analysis will provide answer to your concern.

BTW, I think you should take note on Dik's comment, it might alleviate your concern.

Tristan861:
But, when the conc. structure (cantilevered conc. beams/slabs) above deflects, and many structures do tend to do that, those diag. structs will be loaded. As is usual these days, there are no dimensions or loads shown, no explanation of how the “Inclined steel frame” works or is loaded due to its own usage and function, no clear details of how the frame is built, etc., so how to do much more than guess at how the thing might work? If the top is really free to move, without loading from above, then get rid of the pink connection detail at the top of the frame. Tie the diag. struts back with the top couple (or top one) gray horiz. pieces, and tie the two sides together with the front couple horiz. members, maybe a horiz. x-brace at the top. Then, the diag. struct might still see some moments at the bottom connection, depending upon how that is detailed.

KootK
Thanks

retired13

The post is inclined, so the vertical loads on frame will try to bend the post if there is resistance from the top. Am I right?

I mentioned that the post is designed to be free at top in my model and it is stable.

Thanks everyone.

No and yes. No, the post not likely to bend, or the bending will be very small and negligible, as the load points are laterally restrained by the horizontal members thru tension. Yes, the link will share load from weight of the steel frame, and the horizontal members, if they are subjected to external load. My concern is rotation of the concrete roof in a seismic event. But if that's not a problem, I think everything is fine.

retired13

Seismic load is not a concern in that area.

Thanks,