moment anchorage for columns
moment anchorage for columns
(OP)
Hi, I'm designing a new 31,000 sf building with no exterior walls. the column bays are 30'-9" oc and the roof is at 23' aff, flat, and supported by k joists and joist girders.
Wind loading isn't a problem because there are no walls, but to resist seismic (5% of DL) I was thinking of embedding the columns into their pedestals. Does that sound like it would work, and how do I determine the embedment depth?
Thanks.
Wind loading isn't a problem because there are no walls, but to resist seismic (5% of DL) I was thinking of embedding the columns into their pedestals. Does that sound like it would work, and how do I determine the embedment depth?
Thanks.






RE: moment anchorage for columns
I see other challenges. Concrete is done by one sub. Steel is done by another. It's difficult to even get anchor bolts placed correctly. It's going to be much more difficult to get a steel column delivered, plumbed up and supported while they're pouring concrete around it. And the interface is notorious for corroding.
Another problem is the foundation design. Ther are ways to develop a moment in a foundation, but many of them depend on passive pressures. To get to passive pressures requires a large movement.
I'd consider moment frames that are pinned at the base. You might have to replace some joists with wide flanges, but you'll have less construction problems.
RE: moment anchorage for columns
I would prefer a bolted base detail for the reasons given by Jed, but I would not necessarily design it as hinged.
BA
RE: moment anchorage for columns
But like the others, I would prefer not to embed the column. I would be looking to bolt it down to the foundation. And I would not also just go with a "hinged" design assumption, especially if using tube columns. I like to check both conditions, looking at stress levels and deflection at each. Then knowing that reality is somewhere in between, I come up with my best guess at what reality will be. I like to design the connection to the foundation as fixed, as generally, the connections will achieve a high level of fixity to the base, particularly with tube columns, where the anchors are always outboard of the column flanges.
For very lightly loaded columns, your foundations could get very large to provide adequate over turning resistance. You might consider drilled piers instead of spread footings (which would also work well if you were embeding the column). Might result in less expensive foundations. You could also look at doing grade beams, but I think your column bays are too far apart for these to be efficient.
RE: moment anchorage for columns
RE: moment anchorage for columns
It is really a matter of checking the bearing stress with a couple of extra bars at the top to prevent bursting.
RE: moment anchorage for columns
RE: moment anchorage for columns
If you are embedding the columns, I would detail a pad which you can stand the column on. Have shear studs welded to the column and then place concrete around the column for embedment. Someone did post a detail for this a few months back which I will try to did up.
RE: moment anchorage for columns
thread507-278242: Foundation Design for Fixed Base Steel Moment Frame