Corner Baseplate Example 1

[EngDM]

Typically I have been using Simpson or Hilti's anchor design software to aid in the design of baseplates for cross bracing applications. However, my current configuration is giving the old "Itteration Failed" error in Simpson. The load Simpson accepts before the error is much lower than my design load.

Does anyone know where I can find an example of the design of this baseplate shape? The CSA Blue book does not really help with baseplates all that much aside from some standard square ones.

Need to determine the thickness required of plate and force in the anchors, though for the latter I'm sure I could interpolate Simpson's values. Breakouts are going to be restrained by the grade beam reinforcing since my gradebeam is at a corner.

 

[Celt83]

Force in the anchors if you assume rigid plate is a non-linear solution, there is the white paper by Bentley that describes a newton-raphson solution method.

For the plate thickness I usually look at is bending about the face of the HSS and for the tension anchors a similar bend plane that design guide 1 uses.

 

[EngDM]

Force in the anchors if you assume rigid plate is a non-linear solution, there is the white paper by Bentley that describes a newton-raphson solution method.

For the plate thickness I usually look at is bending about the face of the HSS and for the tension anchors a similar bend plane that design guide 1 uses.

Hilti doesn't return an itteration error for my inputted load so maybe I can use that for force in anchors. One issue I have found is that in the Hilti report it shows my concrete stress being VERY high. I guess just increase the legs of the baseplate until the compressive stress isn't an issue?

Since the force in my anchors is different for the pair (I.E. one is slightly larger due to prying I imagine) do you take the sum of the anchor loads for bending about the face of HSS?

 

[Celt83]

Hilti doesn't return an itteration error for my inputted load so maybe I can use that for force in anchors. One issue I have found is that in the Hilti report it shows my concrete stress being VERY high. I guess just increase the legs of the baseplate until the compressive stress isn't an issue?

Since the force in my anchors is different for the pair (I.E. one is slightly larger due to prying I imagine) do you take the sum of the anchor loads for bending about the face of HSS?

Yeah that is, in my opinion, a huge fault in Hilti's tool they do not explicitly check the bearing stress unless you use the subscription service and do the FEM analysis.

 

[Celt83]

For the anchor tensions I think Design Guide 1 - Example 4.7-7 might be appropriate to reference for how they handled the anchor tensions for the plate bending check.

 

[EngDM]

For the anchor tensions I think Design Guide 1 - Example 4.7-7 might be appropriate to reference for how they handled the anchor tensions for the plate bending check.

Where is example 4.7-7? All I see in my copy is 4.7, Large Moment Base Plate Design.

Is there a separate document with more DG1 examples?

Reference from Celt was for 3rd edition.

 

[Celt83]

third edition of DG 1 came out earlier this year: https://www.aisc.org/Design-Guide-01-Base-Connection-Design-for-Steel-Structures-Third-Ed

 

[EngDM]

third edition of DG 1 came out earlier this year: https://www.aisc.org/Design-Guide-01-Base-Connection-Design-for-Steel-Structures-Third-Ed

Taking a look at your baseplate calculator on your Github, trying my best to follow along. Where is plate thickness displayed or inputted? The inputs/outputs seem to agree pretty well with what Simpson does as far as anchor reaction, concrete stress etc, but I can't seem to find a cell that shows thickness required to satisfy the Mr?

 

[Celt83]

Taking a look at your baseplate calculator on your Github, trying my best to follow along. Where is plate thickness displayed or inputted? The inputs/outputs seem to agree pretty well with what Simpson does as far as anchor reaction, concrete stress etc, but I can't seem to find a cell that shows thickness required to satisfy the Mr?

No thickness input in that one it assumes a Rigid plate, I never got around to coming it with a general design solution method for the base plate thickness so it is just a rigid plate analysis tool.

 

[EngDM]

No thickness input in that one it assumes a Rigid plate, I never got around to coming it with a general design solution method for the base plate thickness so it is just a rigid plate analysis tool.

Ah so it's more for finding loads in anchors and compressive stress under the plate, as opposed to finding thickness. It just assumes the plate works without yielding?

 

[KootK]

I guess just increase the legs of the baseplate until the compressive stress isn't an issue?

The opposite, at least as far as compression + shear goes.

For most arrangements, the base plate projections beyond the column face will be worthless as far as resisting compression load goes. Commensurately, a reasonable design approach is often to simply ignore them for that purpose and use them only for shear transfer / uplift.

It will take a very stiff column to be able to mobilize the projections for compressive resistance. No way you have that if your case is the usual one of a scrawny HSS buried in a light frame wall etc. You know, unless it's 6" tall.

 

[EngDM]

The opposite, at least as far as compression + shear goes.

For most arrangements, the base plate projections beyond the column face will be worthless as far as resisting compression load goes. Commensurately, a reasonable design approach is often to simply ignore them for that purpose and use them only for shear transfer / uplift.

It will take a very stiff column to be able to mobilize the projections for compressive resistance. No way you have that if your case is the usual one of a scrawny HSS buried in a light frame wall etc. You know, unless it's 6" tall.

Hi KootK,

I'm referring to the compression imposed on the concrete from the outward legs in an uplift case. Any plate past the row of anchors seems to be in compression, so by increasing their length I'd imagine that shaded grey zone would benefit?

 

[KootK]

Any plate past the row of anchors seems to be in compression, so by increasing their length I'd imagine that shaded grey zone would benefit?

Yup, at least in theory. That will all be pretty sensitive to the stiffness of the concrete, the stiffness of any grout, and any pretension in the bolts. It's a bit of an odd thing to rely on prying action for resistance. It's done but usually as a last resort.

My first instinct would be to treat the projections as simple cantilevers (from the column face) and take that as the likely upper limit of useful uplift resistance. I would be more keen on the prying mechanism with stiffeners in play but you won't have much space for that.

If the simple cantilever thing works, I wouldn't sweat the prying compression under the base plate. Just minimize the bolt edge distances to the usual.

 

[EngDM]

Yup, at least in theory. That will all be pretty sensitive to the stiffness of the concrete, the stiffness of any grout, and any pretension in the bolts. It's a bit of an odd thing to rely on prying action for resistance. It's done but usually as a last resort.

My first instinct would be to treat the projections as simple cantilevers (from the column face) and take that as the likely upper limit of useful uplift resistance. I would be more keen on the prying mechanism with stiffeners in play but you won't have much space for that.

If the simple cantilever thing works, I wouldn't sweat the prying compression under the base plate. Just minimize the bolt edge distances to the usual.

Going through this baseplate configuration I'm finding that anchors 1 and 4 in that photo are taking basically all of the load. Would you add 1+2 reactions and use the full plate leg width for your simple cantilever? Or use the higher reaction with half the width.

 

[KootK]

Going through this baseplate configuration I'm finding that anchors 1 and 4 in that photo are taking basically all of the load.

Right, but that is very much a product of the utilization of that prying mechanism.

Would you add 1+2 reactions and use the full plate leg width for your simple cantilever?

That one. It probably is a bit unconservative for the reason that you noted. The prying action will, to some extent, be "real" behavior.

I just don't feel that there's a good way to capture more accuracy in a meaningful way so, you know... keep it simple.

It would be nice the anchors could be overdesigned to yield the plate but that probably isn't realistic here.

 

[Celt83]

Ah so it's more for finding loads in anchors and compressive stress under the plate, as opposed to finding thickness. It just assumes the plate works without yielding?

yes the spreadsheet is only for finding anchor tensions and compressive stresses, it assumes the plate is rigid in my experience keeping the plate below yield was one method folks would use to rationalize "rigid" behavior but looking at the new FEM results that Hilti, Simpson, ideaStatica, etc. produce I'm not sold on that being the best criteria.

How much tension are you trying to transfer with this corner connection?

 

[EngDM]

yes the spreadsheet is only for finding anchor tensions and compressive stresses, it assumes the plate is rigid in my experience keeping the plate below yield was one method folks would use to rationalize "rigid" behavior but looking at the new FEM results that Hilti, Simpson, ideaStatica, etc. produce I'm not sold on that being the best criteria.

How much tension are you trying to transfer with this corner connection?

Total uplift of 96kN. Any tension breakout is going to be resisted by developped stirrups in my grade beam and dowels into the pile. Just need to rationalize a good way to size the plate.

One thing I tried as setting different loads in Simpson before the itteration fails, and then plot the force-thickness and fit a curve, which was basically linear and find a relationship like that for my load. Then I bumped it up quite a bit to 1" (an increase of like 30% from my plotted relationship) and a nice round number.