Hello again. I have decided to run an elevated line along the fence that runs down the side of my property. Just to connect the main area to a small town area thing. Not really important info but everyone likes a little background. My issue is this: The run is about one hundred feet so I will need many piers, or abutments if you’d like. Right no the plan is to sink three/four foot six inch diameter forms and fill them with concrete flush to ground level to use as a base. Now I just need to work out the piers themselves. I was thinking of trying cast cement or concrete. Has anyone attempted something like this? I could use some proper advice on this. I’m not sure of the exact design but I’m sure it will be modestly detailed so casting shouldn’t be that big of a deal. Specs are rough at this point but let’s go with just under three foot height to the deck and wide enough on top for a pair of rails. Something that flares out toward the base. I’m not sure about spacing yet as I have not decided which style of bridge to use. I guess I could use some input on that as well!
Hi Mark,
I did one concrete pier over on the “modeling site” http://www.largescalecentral.com/forums/topic/18390/a-bridge-build-for-the-little-ri The actual concrete casting of the pier is on page 3.
I used foam insulation board to make the mold. Others have used plywood forms to make the molds.
Hope this is helpful. Good luck with your project.
Tom
Mark,
Several comments come to mind.
Depending on where you are located, be sure to sink your forms deep enough to be below the local frost line. This will keep them from trying to rise up out of the ground during the freeze / thaw cycle. I would recommend being at least 1 foot deeper than the recommended frost line depth. (Personal experience living in the north east.)
I would also determine what the widest portion of the base of the piers will be and make your foundation form that dimension or a bit larger. Also, I would add a piece or two of reinforcing rod (say a #4) protruding up about 6" out of your foundation to lock your piers to when you pour them in place.
Based on the anticipated height, I would recommend a reinforcing form inside the pier of that good old fashion hex shaped ‘chicken wire’. This will aide in strength should the piers be ‘bumped’ by anyone. Concrete is a great material in compression, but it is very weak in bending. The steel chicken wire will pick up the strength in bending.
Sounds line an ambitious project, looking forward to seeing some pics along the way.
Bob C.
PS - A #4 reinforcing rod is 1/2" nominal diameter.
Tom- Thank you for the link. Very helpful.
Bob- I’m just outside Chicago so my frost line is almost four feet which makes this a pretty big project. I was thinking about casting the pier bases off-site and simply setting them on the pre-sunk foundations. I figure their weight alone should keep them from shifting. That way I can remove and reuse them if I should change anything down the road. Good call on the chicken wire.
I use hardware cloth for reinforcement in small pours. It is a lot stronger than the chicken wire.
The biggest problem I’ve had in casting concrete has been air pockets. I’m told an orbital sander without paper can be used as a vibrator on the outside of a form but I’ve never tried it,
I use plywood for forms sprayed with WD40 as a mold release and have had mixed results depending on how complex the shape being cast.
If your piers will be less than 6 inches square you might want to mix concrete and mortar mix 50/50. This reduces the amount of aggregate making the mix better able to comply to small areas.
One of my more involved concrete projects was Deep Cut Tunnel; documented here: http://www.largescalecentral.com/forums/topic/12414/cvsry-over-engineering-dept-pro/view/page/1
Ice is a powerful tool. Any moisture that gets between the foundation and the bridge pier can make it move. If you don’t want to make it permanent, possibly use a piece of rebar as I mentioned above, but include a sleeve in the pier to slide over the rebar. This will lock the base from moving, but still allow easy relocation of the pier (or removal) at a later date.
@Jon,
I don’t disagree with the hardware cloth being stronger, but the chicken wire is far easier to form. Also be aware that ‘chicken wire’ as we think of it can be gotten in heavier gauge wire that is usually stocked at HD or Lowes. Check out McMaster-Carr, I ordered some fairly heavy stuff some years ago, in stainless nonetheless.
Bob C.
Concrete supply/delivery plants started years ago using fiberglass “rods” short glass string sized pieces in their deliveries for a mat-like reinforcement. I have used it frequently for patio slabs and walkways over a tamped stone base in lieu of welded-wire fabric or rebars. The finish is “hairy” but that wears off quickly. For smaller dimensional pours, I would suggest looking to something like this. Steel inside concrete will often rust and cause the concrete to fail. Look at our roads and bridges.
FYI, I am in Planting Zone 6, building code here requires 36" deep footings.
I like the idea but I may flip it. Mortice the anchor and tenon the pier. I like the idea of having the anchors, which is what I’m calling them, flush with grade. No tripping and not problems mowing. I completely forgot about fiber additives. From what I’ve read they are the way to go. Thanks.
Glad we could be of confussion…errrr help.
Bob C.