How rigid is a 1" x 4" flat bar ?

[bdog]

How rigid compared to what? Normally in situations like this, absent any other information about loads, I would take the normal/recommended structural steel and compute it's characteristics, and then compare that to the type of steel I want to use. That way you get a quantitative answer as to how it compares.

So, what would they normally use? Take that shape, compute the area moment of inertia, and then compare to the area moment of inertia of 1x4 bar.

If loaded against the 1" dimension, the area moment of inertia of a 1x4 bar is going to be 4*1^3/12 = 0.333 in^4. If loaded against the 4" dimension, it would be 1*4^3/12 = 5.333 in^4.

Now make the area moment of inertia calculation for the standard shape normally used, and decide if your 1x4 will cut it. Maybe you'll find out you need a 1.5x4 or something just a little larger, who knows.

I don't know exactly what they use but it looks like two pieces of 4" angle aluminum butted together maybe 5/16" or 3/8" thick.

Using your .333 moment and a 12" cantilever the 1" x 4" bar would deflect 0.3" with a 5,000 lb load, 0.6" with a 10,000 lb load.

I am no engineer but it seems to me that I beam in the first picture sticking up 4' pulled sideways from the top would be a lot weaker than a the fact bar only sticking up 12" ? I don't know.

 

[s219]

I am no engineer but it seems to me that I beam in the first picture sticking up 4' pulled sideways from the top would be a lot weaker than a the fact bar only sticking up 12" ? I don't know.

I would think so too, but it really depends on the I beam characteristics -- they are very stiff shapes. That is more of a beam, and what you're proposing is more of an anchor. For your case I'd think that the underground portion is probably the part that matters most, and there you are at the mercy of the soil. I know when I ran wind load calculations for pole barns a few years ago, the soil was going to give out and let the pole push over long before the wood was going to crack.

 

[bdog]

I have an 18” auger and plan on drilling the hole 5’ deep. They will take about 14 80lb bags of concrete each to fill up. I would think over 1000lb of Concrete set 5’ deep would do the trick?

With a pole barn you have a lot of leverage working against you especially with tall buildings. The force on this will be applied down low.

 

[Dutch445]

is this a "floating dock"?
or is the dock setting on the ground and you just wish to stabilize
the 2nd story of it?

 

[bdog]

The dock is fully floated. The gangway is mounted and anchored to the shore and I am sure it adds some support as well as the stiff arms. The contractor is doing that part. I just didn’t like the look of the stiff arm mounts and wanted to do them myself and make them less noticeable

 

[Dutch445]

i guess i'm having a hard time understanding why you would put a floating dock
in a pond that you own, that has minimal fluctuation in water level, and does not
need to be removed for winter like us up north.. i would just as soon build a
2 story deck on the edge of the pond with a bit of cantilever if i couldn't
support straight down into the water.
but with your floating dock, is the stiff arm system tied to the upper level as well
as the lower level?

 

[swines]

You might want to think about using a different shape for the anchor post. 6-inch diameter, schedule 80 pipe filled with concrete with a concrete foundation. Then weld a 1/2-inch thick plate to the post at the required level for the dock connection. If you want it to be extra stiff - put gussets between the post and the plate for additional reinforcement. You can cap the top of the pipe with a convex, concrete surface (like a bollard).

 

[CincyFlyer]

The dock is fully floated. The gangway is mounted and anchored to the shore and I am sure it adds some support as well as the stiff arms. The contractor is doing that part. I just didn’t like the look of the stiff arm mounts and wanted to do them myself and make them less noticeable

Consider finding some sort of small plastic barrel, and cutting it to fit over that anchor point to dress it up.

 

[swines]

Another approach would be to use the I or H beam, drill the bolt holes, put the bolts in through the back and tack them in place so they become studs. Box in the sides and top by welding sheet metal to the beam. In that way, you'd turn the beam into a box above ground.

 

[Ford850]

You might want to think about using a different shape for the anchor post. 6-inch diameter, schedule 80 pipe filled with concrete with a concrete foundation. Then weld a 1/2-inch thick plate to the post at the required level for the dock connection. If you want it to be extra stiff - put gussets between the post and the plate for additional reinforcement. You can cap the top of the pipe with a convex, concrete surface (like a bollard).

This gets my vote. Best looking, safest, and probably the strongest.