portable concrete benches

M

mike cockcroft

New member
I am building 12 concrete topped portable (movable) benches. 3.5 ft x 3.5 ft. with 12x12 knockout in corner. Using 4 in. channel iron with 1/2 in rebar mat.
4.5 in thick. Picture shows form and steel. Ater pouring and letting set for 7 days we will flip them over and weld 2 7/8 in pipe legs to three ends of channel iron.
Will move them on and off concrete firing line to permit prone shooting.
Anyone see any problems with this design or idea?
This is the first one, the next ones will have longer channel iron to move the legs about 2 more inches towards the sides of the concrete top.
Will use my tractor with forks to move them around.
http://i49.photobucket.com/albums/f260/cockcroft/2010_05_03_IMG_0041.jpg
 
150 pounds per cu. ft.

Each bench is going to weigh more than 700 pounds.

Concrete weights about 150 pounds per cu. ft.

3.5 x 3.5 x 0.375 = 4.5938 cu. ft

4.5938 x 150 = 689.0625 pounds plus the rebar, channel iron and 2 7/8 inch pipe legs.

Just make sure the tables have provisions for the fork lift's forks.

Your tractor my not handle the weight.

I am not certain the concrete will like the heat produced by the welding.

The knockout needs to be 18 inches long and the 12 inch width might just be enough.

I think mocking one up with a wood top to see how it fits would be a good idea.

Best wishes
 
Have you ever welded on concrete? From what I'm seeing you're setting yourself up for some serious bustification...... wear a face shield if you're gonna' weld those legs on after. I would weld them up before, easier to pour and finish too, troweling at your bellybutton is a whole lot easier than on your knees!

I've only watched concrete blowing apart twice, once because our long-haired nature guide had us built weeny roasting fires on a concrete slab when I was in grade school and once when a guy was welding stuff ON the floor in a shop. Both instances left a lasting impression.

I could be over-thinking the issue because I've honestly never tried what you're doing.....We in the industry just never set up the way you're attempting to do.

al
 
I weld for living. Attaching the legs shouldn't be a problem, I weld on concrete coated pipe all the time while welding steel water lines. The problem comes from superheating the moisture in the concrete, the concrete itself is basically inert. It may pop a little while welding or soon after, just wear eye protection when you are near the hot sections, it would be similar to hitting the concrete with a hammer.
 
Mike ...

mike cockcroft said:
I am building 12 concrete topped portable (movable) benches. 3.5 ft x 3.5 ft. with 12x12 knockout in corner. Using 4 in. channel iron with 1/2 in rebar mat. 4.5 in thick. Picture shows form and steel. Ater pouring and letting set for 7 days we will flip them over and weld 2 7/8 in pipe legs to three ends of channel iron. Will move them on and off concrete firing line to permit prone shooting. Anyone see any problems with this design or idea? This is the first one, the next ones will have longer channel iron to move the legs about 2 more inches towards the sides of the concrete top. Will use my tractor with forks to move them around http://i49.photobucket.com/albums/f260/cockcroft/2010_05_03_IMG_0041.jpg
Click to expand...

Unless you're real keen about moving 400+ lbs benches around, you might want to consider building a soil pad with grass in front of the benches and anchor the concrete benches in place.

Below are some pictures of the Austin Rifle Club's "C" range that was built for a national match back in the 70's. You'll see little stakes [with numbers on them] in front of the benches. Those denote the 40 prone positions that are used by our High Power shooters in front of our 40 BR benches.

Just an option you might want to consider. It also allows you to save $$$ on equipment needed to move the benches and the time and manpower need to break down one line and then set up the other. :)
 

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agree

At our range we have fixed concrete benches and for prone shooting we lay in front of these benches.

Also notice how long the cut out is on the benches pictured.
 
jlmurphy said:
I weld for living. Attaching the legs shouldn't be a problem, I weld on concrete coated pipe all the time while welding steel water lines. The problem comes from superheating the moisture in the concrete, the concrete itself is basically inert. It may pop a little while welding or soon after, just wear eye protection when you are near the hot sections, it would be similar to hitting the concrete with a hammer.
Click to expand...

And I pour concrete for a living :) And that concrete is going to have a high water content for weeks IMO. I do footing and wall forming and for structural work all welding within an inch or so of the 'crete has to be pre-fabbed, we pour it in with tabs sticking out through the formwork. Even tiltups anymore are perty much all pre-tabbed or slip-joined as far as I'm aware.

But I'm NOT a welder, I'm just preparing for them. Maybe there are cases where they can crank the heat up and zap right on the concrete surface.

al
 
Benches

I had the same problem at our range. I made up 4X4 X1/8 Square tube stands. I added 4 inch steel wheels to the front legs 1/8 inch off the bottom.
A $19.00 trailor jack to the rear leg. Jack the rear leg up 2 inches and a 12 year old can move the benches around the pad. I poured the cement tops at home and with an engine lift could put three benches and tops in my truck. Tops are bolted to 2 1/2 angle iron welded to the legs.
Our covered firing line is 150 long. With the left side 200 yards and Right side 100/ 50 yards. Takes 1/2 hr to move 9 benches.
Cement top uses 4 80 lb and 1 40 lb bag. is 3 1/2 thick with rebar.
Benchrest41810holbrook001.jpg


Paul
 
Al has a point due some consideration. However, imbedded steel welding plates are common in construction. I have used them in tilt up concrete walls with satisfaction. This is common practice in our region.

just a suggestion, weld one leg at a time and let the steel cool before welding the next. I wouldn't heat the steel channels too much to avoid expansion.

The concrete might crack from the expansion of the steel. This would be a waste of work and material but it should not be dangerous.

Concho Bill
retired observer
 
Paul.
Those benches look like the ones at WWCCA Plymouth, MI.
Except for the wheels and jacks. We use a converted Pallet jacket. With an angle iron rig on top the legs of the Pallet jack. Pump the jack up and they move real easy.....:)
 
Movable benches

Those comments are quite good.

It is vise to make a mock up to determin best hight and best dimentions. As has been pointed out I think the cut out from the bench tops are not optimal but you find that out if you build a mock up top.

Also it is important to have about 1/4 inch thick rubber squares glued under the legs to taka away vibrations.

Do not paint the surface of the table tops with thick and slippery oil paint as the rearbag will slide and so will the rest. I had to glue a 3/4 plywood on the top to stop that.

If interested I have pictures drawings etc of building such benches I can mail them to you.

To move the benches a pallet jack is very handy and easy to operate. We welded vertical iron bars about 2 inches lower than the lower surface of the tops onto the pallet jack. Then it can be driven under the tops jacked up and the tables moved.

bergur@lsh.is
 
Slippery benches

Try some rubberized perforated shelf paper to keep rear bag from sliding
if you have slippery bench tops.
 
Having been in the construction business for 30+ years, we also set steel anchor plates in concrete and weld I-beam or pipe columns to them all the time. You are correct, the corner knockout needs to be 12 x 18. Might have to weld a cross brace between the front two legs and maybe a diagonal brace from the center of the back leg up to the channel iron.
As far a weight goes, a 65 horse power tractor will move them no problem.
I have issues with terrain elevations that keeps me from shooting prone in front of the concrete pad. I had to build a clay pad to raise the elevation of the shooting deck to allow us to shoot prone without bullets hitting a rise in the pasture. Having to overcome several obstacles to make this work for different shooting styles.
Will get the first on made and report back.
 
.25shooter said:
Those comments are quite good.

It is vise to make a mock up to determin best hight and best dimentions. As has been pointed out I think the cut out from the bench tops are not optimal but you find that out if you build a mock up top.

Also it is important to have about 1/4 inch thick rubber squares glued under the legs to taka away vibrations.

Do not paint the surface of the table tops with thick and slippery oil paint as the rearbag will slide and so will the rest. I had to glue a 3/4 plywood on the top to stop that.

If interested I have pictures drawings etc of building such benches I can mail them to you.

To move the benches a pallet jack is very handy and easy to operate. We welded vertical iron bars about 2 inches lower than the lower surface of the tops onto the pallet jack. Then it can be driven under the tops jacked up and the tables moved.

bergur@lsh.is
Click to expand...

25,

Do you have pix of the one-piece benches used at the WBC in Sweden??

awesome

al
 
I in my infinite wisdom once made a fast and furious campfire on a rain soaked concrete pad.
Not a mistake I'll make again any time soon:D Sounds like firecrackers and small chunks of concrete were raining down in a 30yd circle. Pretty tough to dry your clothes when your running away from superheated concrete projectiles:D

FWIW I would'nt recommend welding those rebar either. Welding weakens, hardens and causes brittleness and premature rust in rebar.

Once again using my superior intelligence I was bending a whole bunch of #7 (7/8")rebar left vertically exposed in a concrete foundation. The idea was to get them to line up with the cores in our masonry block wall.
All was going well until I got to the one a steelworker had used to mount a welded temporary brace for a steel column.
That one did'nt bend. It snapped right off sending me off the scaffolding.
When I finally came to the safety officer asked me how this accident could be prevented. Simply told him you should'nt weld rebar I quess:D

Al would know more about this than me. Rebar is usually wired together in my expierience. Welding is verboten.
 
One point I don't see discussed is the lateral stress factor for your benches. You're loading three vertical members with an awful lot of weight which, if subjected only to compressive loads, should work. But when you're moving them about and "dragging" the legs (that's inevitable) to get them into position you're putting lateral stress on the welded joints and it one of them fails the entire mass falls - not a pretty picture. I'd suggest giving some consideration to cross bracing your supports to reduce the lateral stress impact on your design.
I also would not weld the rebar - for all the reasons listed.
 
Mike, why portable?
When you can leave enough room between benches for prone shooting.
These are the benches we're building in Crosby Tx

G.A.

 
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It is easy for us to criticize someone else's work but how many of us have actually taken the time to build some benches?

Some of us have worked with concrete construction and we have learned a lot of what we know by the mistakes that we have made.

There is nothing wrong with that bench that isn't better than no bench at all.

So the joints are welded instead of wired. Big deal! The steel in that bench is over engineered anyway. If it needs some additional lateral bracing, it can be added.

Keep at it Mike. It is funny how only those who do things get criticized.

Concho Bill
 
Mike
We use 40 portable concrete benches at Sacramento all the time.They weigh around 400 pounds plus and we move them with a quad runner because of the distance they will be moved.
I didn't build them Bob Dorton did and he uses a long beam with a trailer ball on it that fits on the quad runner.You roll a axle under each bench and when you lower the beam the bench is lifted off of the ground and connected to the quad.We them drive them 150 yards to the line roll them into place and they are good to go.
This comes up quite a bit so the next time I am there I will take some pictures of how we do it at each match.It is very simple very easy and very cheap.
If you PM me I will give you Bob's phone number and he can explain how it is done.
Lynn aka Waterboy
 
I know you arn't supposed to weld rebar. I did it so I could pick up the whole steel and move it. I will look at leg bracing after I get them welded on and the bench turned over. This is a practice run. Thanks for all for the advice.
The reason I want to make the benches portable is so I can get more shooters on the line for a prone match. Maybe I'm making this too difficult but I want to be able to use this range for multiple purposes. And if I go broke we can store hay or equipment under the roof!!!!
 
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