Anchor Bearing Plate Thickness 1

[gre2408]

I am currently working on designing a size of anchor bearing plate for 45 ft. high anchored soldier pile wall and want to get your advice on it. Initially I simply tried with a simple beam model to design the thickness of the plate, but after finishing the calcs I thought that the number I came up with was too high. Now I am trying to use one of formulars for flat plate in Roark's stress strain formular book and not so sure which case in the book I should use. Any thoughts on this?

 

[InDepth]

It depends on how you are detailing the plate. Do you have sketch to post in order to determine the edge support conditions and plate dimensions?

 

[born2drill]

Follow your loads! Take a look at an anchor head setup - the tieback load is being transfered into a hex nut or anchor head, which then sits on the bearing plate. Your load is distributed in a donut shape onto the bearing plate. Modeling this as a simply supported beam with a concentrated load in the center will give you much higher moments! (What did your initial analysis come up with anyway?)

There are many variations on this setup, so you will need to know the span, diameter of the center hole and diameter of the anchor head (these will vary greatly depending on whether you use strand or bar anchors).

Another factor to consider is whether you design around the anchor design load or test load (typically 1.33*DL). This will depend on the type of jack chair you use while testing. You also may be allowed to use a 20% overstress in the steel depending on if this is a temporary or permanent wall.

Many of these details vary by contractor preference, which is why most of them design their own work to fit with their methods.

 

[PEinc]

Good answer, born2drill. However, flat plates are already designed for 0.75Fy in bending. An extra 20% gives 0.90Fy (getting pretty high).

 

[born2drill]

True. I should have been more specific about %Fy rather than just talking about an overstress without discussing what we are overstressing to begin with! I keep it under 80% Fy.

 

[gre2408]

That was what I was thinking, too. As born2drill suggested, I will stick with the number originally come up with. Thanks!

 

[PEinc]

What Roark Formula number were you using?

 

[gre2408]

The closest model I found was case 2k (outer edge free, inner edge simply supported). In my case, anchor is installed through pipe lookout welded in h-pile and 7 strand anchor head bears on the steel plate sitting on pipe lookout.

 

[PEinc]

If you have a bearing plate with a strand anchor head and if the bearing plate is sitting on the projecting end of a pipe sleeve and if the anchor head diameter is less than the pipe sleeve inside diameter, then you probably should be using Roark Formula 1a (outer edge simply supported, inner edge free) on page 400 of Roark's 6th edition.

I would use Formula 2k if I had a bearing plate sitting on concrete (as for dam tiedown anchors) and the hole in the concrete has a larger diameter than the diameter of the anchor head.

Comments?

 

[TexCE2009]

Is there a good reference out that would give examples of how to design the bearing plates and anchorages attached to a steel pile or a drilled shaft for tied back walls?

 

[jdonville]

All,

Talk with your anchor tendon manufacturer. Many are happy to provide this kind of support (and have engineers on staff to do the work) provided that you have bought your system components from them.

We routinely use (for example) spreadsheets provided from DYWIDAG Systems International for the design of bearing plates with DYWIDAG bar and strand tendon anchors.

Jeff