base plate design ignores corners of base plate

huangyhg

base plate design ignores corners of base plate?
the cantilever method for rigid base plate design per aisc seemingly ignores the areas of the base plate that aren't directly perpendicular to the column.
in other words, there is no check for the corners of the steel base plates.
i'm sure this is fine for a small base plate, but what about for a relatively large base plate, where the area of the corners of the base plate is more than the area that is directly perpendicular to the column?
is there a rationale for ignoring the corners of the base plates?  
prior successful performance?  "we never worried about it, and we never had a problem with it?"  i'm not sure, so i'll let others chime in.
the line across the diagonals is usually wider than the width of the base plate. i.e. it is a greater effective width.
also check that your base plate dimensions are not outside the recommended limits (i believe there are some somewhere)
the rigid baseplate analysis always has bothered me.  risabase actually does a finite analysis of baseplates which gives really interesting (but sensible) contours of loads.  it is interesting on the side where the baseplate is in an uplift condition, the corners past the anchor bolts go back into compression because of the stiffness at the bolt.  good program but takes some time when analyzing.
akastud
akastud-
wouldn't you expect the basplate to back into compression on the side of uplieft on the far sde of the anchor bolts?  that is where the prying forces come from.
you're welcome to check that pattern.  it shouldn't control because that yield line is so long and because the resultant upward force is only about 1/3 from the corner of the column to the corner of the plate.
271828, can you explain that?
the case i'm asking about is for axial compression only.  there would be no uplift due to bending / tension in the base plate.  the upward force on the base plate would be the allowable bearing pressure, and would be uniform under the base plate.
csd72, i couldn't find any limits on base plate dimensions, either generic, or related to a design theory.  my guess is it's because base plates are sort of in between steel design and concrete design, and so neither aci or aisc like to go into too much detail on them.
sure.  
the proposed yield line cuts diagonally across the base plate near the flange corner.  the part of the plate outside the yield line is the triangular (or close to triangular part) part near the corner.  
if the pressure is uniform over this triangular part, then the resultant force is about 1/3 the way from the yield line (which passes through flange corner, or close to it) to the corner of the plate.  this is more favorable than if the resultant was halfway between the yield line and the edge of plate, which is the case for the typical patterns shown in the aisc manual.
aggieyank, why are you worrying about this?  steel design manuals and the aisc manuals give the design method for column base plates.  why not just use what has been successfully used for years?
271828, correct me if i'm wrong, but doesn't the n', the yield line theory cantilever distance, refer to the distance inside the flanges, and not account for anything outside the flanges?  i didn't quite follow your explanation.
peinc, i'm trying to design a base plate for a temporary steel structure that sits on soil.  the base plate is relatively large compared to if it was sitting on concrete.  i don't think the traditional rigid plate cantilever method property accounts for large areas of the corners of the plate, but couldn't find a design method which addressed this issue.
right now, i'm planning on designing based on the cantilever method, and increasing the thickness some nominal amount.
aggieyank-
i see your question.  the formula for the thickness of the baseplate does it on a per inch basis (along the length/width of the plate).  it basically assumes that every inch of b has a support inch at the critical section line.  
i believe aggieyank's question is how is this possible since the column is providing the support for the cantilever baseplate and the column does not extend all the way along the creitical section line (along either the b or n dimension).  basicaly, should the moment capacity of the plate be determined based on the acutal column dimension and the required moment capacity be determined based on the entire trib area, instead of assuming it on a per inch basis since there is a distance (b-bf) thast has no cantilever support.
does this represent your question aggieyank?