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

[bdog]

I am getting a 15' x 30' aluminum two story fishing dock installed. The pond it is going on has a plastic liner thus no anchor poles in the water. The manufacturer use two stiff arms, one on each side, to anchor it to the shore.

Below are pics of how they recommend doing it. Basically an I beam is set in concrete and then they supply a T shaped aluminum bracket that bolts to the I beam and then the stiff arm bolts to the bracket using a 1" bolt.

My setup at my pond is different in that my water level does not fluctuate as it is well fed and the ground is flat leading up to the pond. Instead of my stiff arms being attached 3-4' above the ground they will only be 12" above the ground.

I was thinking of using 1" thick by 4" wide flat bar set 5' deep in concrete for this and then simply drill a 1" hole in it. It will provide a much cleaner look.

The flat bar would only be sticking up 12" out of the concrete. This bar should be rigid enough with only 12" of stick out shouldn't it? Alternatively I could set an I beam and weld a tab to it or use their bracket I am just trying to clean up the look of it on the shore.

 

[NoTrespassing]

I'd recommend angle, T bar, channel, or square tubing before flat bar.

Kevin

 

[bdog]

I know those shapes are surely structurally stronger no doubt, but with only 12" sticking out I am wondering if the 1" x 4" is going to be so strong it won't matter. I surely don't want it to fail but I am going for the cleanest look.

 

[RedNeckRacin]

What happens when you get a slight lateral load on that bar from the wind pushing the dock? It sounds like you are spending some money for this project, use a good structural component. Flat bar is only strong in one axis. If you want to know the difference in strengths, I can look it up in my steel manual for you.

 

[bdog]

Here is a better pic of what the finished product will be like. This one was actually done incorrectly with the mounts too close to the ground as the pond went down and now the stiff arms are contacting ground.

Lateral load is my concern. I doubt the 1x4 bar will bend in the 4" direction. It will definitely be weaker in the 1" direction but still I wonder how strong can those aluminum brackets in my original pictures be? They look to be two pieces of angle welded together and maybe 3/8" each for a total of 3/4". Would a a 1" x 4" flat steel bar only sticking out 12" bend before that aluminum bracket would?

Definitely not wanting to cheap out. Price is of little concern on these anchors. the dock is expensive and I want it staying put. My main goal other than it staying put is have the least obtrusive design possible without something sticking up our out for kids playing around there to run into.

 

[coldsteelva]

I have concerns about a 12" flat bar sticking up out of the ground with no protection. What happens if someone trips and/or falls on this protrusion from the ground?

 

[marchanna]

Here is a better pic of what the finished product will be like. This one was actually done incorrectly with the mounts too close to the ground as the pond went down and now the stiff arms are contacting ground.

Lateral load is my concern. I doubt the 1x4 bar will bend in the 4" direction. It will definitely be weaker in the 1" direction but still I wonder how strong can those aluminum brackets in my original pictures be? They look to be two pieces of angle welded together and maybe 3/8" each for a total of 3/4". Would a a 1" x 4" flat steel bar only sticking out 12" bend before that aluminum bracket would?

Definitely not wanting to cheap out. Price is of little concern on these anchors. the dock is expensive and I want it staying put. My main goal other than it staying put is have the least obtrusive design possible without something sticking up our out for kids playing around there to run into.

I like this version. No need to have a steel bar sticking up at all. You should put some plastic bushings in the bolt holes to prevent galvanic corrosion between the steel and the aluminum.

 

[bdog]

I have concerns about a 12" flat bar sticking up out of the ground with no protection. What happens if someone trips and/or falls on this protrusion from the ground?

It won't be sticking up with no protection. The stiff arm will be bolted to it. It will not be any taller than the stiff arm nor will it protrude out to the sides or even the front or back significantly.

 

[bdog]

I like this version. No need to have a steel bar sticking up at all. You should put some plastic bushings in the bolt holes to prevent galvanic corrosion between the steel and the aluminum.

I don't want those huge concrete pillars. There is no reason for them to be visible they can be below ground and directly under the mounts. Essentially what I want is something just like that picture except with the concrete underground and the mount coming up out of the center of it. Except instead of using a T shape just a thick flat bar.

 

[s219]

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.