Steel: Base Plates

So let's talk about base plates in steel columns. First let's talk about the process. Excuse me. There's some kind of anchor rods that are cast into concrete using some kind of template. We see here a wood template. And it depends on what kind of load the column that's going to be inserted. on these anchor bolts, what kind of load it's carrying, and what kind of wind load it has to do. So, that would determine the length of the anchor rod, or how far down in the concrete it has to go. Clearly, this one here is pretty deep. It must be it's carrying a lot of uplift or wind load, versus something a little bit shallower. So, anyway, here's a template with the anchor bolts on it. The column comes in with the base plate welded and the holes pre-drilled or pre-punched in the fabricator shop. And then the column is lifted and it sits on the anchor bolts. Usually, one of the anchor bolts, the nuts rather, is leveled to a certain point where it becomes the reference, the benchmark. That's the painted one in this image. Now the others have to be leveled based on that one. And you cannot adjust that one because it's set by a level, a measuring instrument, that gives you the level that the column base plate needs to be at. We've seen this video, this animation before, but here it is again. Basically, the anchor bolts are there, the column comes in, and there's some leveling knots that go in there. there's a block out so that the column carrying a larger load would not punch through the slab on grade. So the column has its own foundation because it's carrying a roof load versus the slab on grade, it's just sitting on the ground not carrying a roof load. And then the next thing to talk about is these leveling nuts. So one of them is a reference, and the others are adjusted. If we tighten these two nuts, then the column leans this way. And then we take this one and this one, and we adjust them so that the column leans in the perpendicular direction until it's plumb. The load of the column is sitting on these nuts, And we have to understand that beyond this face of the column, beyond this face, the plate is cantilevered. Beyond this flange, the base, sorry, the base plate is cantilevered. So in elevation, if this load is excessive, then it could curl that plate up. Those are two cantilevers that could curl up versus over here it's supported. There's two dangers. One is the column punches through the plate if it's too thin. That's why it has to be thick enough. And then that cantilever cannot be endlessly large because then it'll curl up much easier. From here on out, the plate is cantilevered. From here on out, the plate is cantilevered. So we have to address that issue. And then the column sends its load to the base plate. The base plate sends it to the nuts below the plate. There is a non-shrink grout underneath the plate. The load is transferred through the anchor bolts into the concrete. There is bearing between the plate and the non-shrink grout that we need to also size the plate for. So here's the non-shrink grout after it's been leveled and everything. There's some waterproofing on the column. And then they pour this separate diamond later. They poured the slab on grade. They poured the diamond later. And these, of course, are control joints to make sure the slab thickness is just a little bit less there. And so any crack in the slab on grade would happen at that point. And here's the detail we've seen before. As long as the anchor rods are beyond the flanges, you will have a fixed end connection, which is represented like this. And if those anchor bolts were within, then it would have been a pin connection. So it's basically, are you on the flange line and beyond, or are you within the flanges, which is on the web, in which case it would be a pinned connection and not a fixed dent.