Completely botched pier rebuild

[Tomatobro]

to achieve that level of integrity the aggregate sizes and cement ratios and water content are carefully controlled and the forming is done in hydraulic moulds.

Not something that can be done in a basic shutter mould unfortunately. I hope the builders can sort it out for you.

[Franklin]

10 minutes ago, vlaiv said:

Those things weigh half a ton and manage to stand still in high winds and all kind of weather.

 

And they go down into the ground 1/3rd of their height.

[Franklin]

24 minutes ago, vlaiv said:

stand still in high winds and all kind of weather.

What about the one in the distance.🤣

[vlaiv]

9 minutes ago, Franklin said:

What about the one in the distance.🤣

That one is made out of wood

(notice brown color)

[vlaiv]

Ok, so I'm learning something new here.

What we have here is failed cold joint.

I'm pretty sure they did not use any sort of adhesive in this case - but I guess they should have done so.

[jetstream]

52 minutes ago, Franklin said:

It's totally fixable, just need some plywood for the form work and another load of concrete.

I'm not so sure that a another slab, pored around the pier (with rebar drilled and epoxied into it) on top of the other would provide what he needs. Even using bonding compound on the pier (or roughed up and "buttered") would most likely not give the wanted stability.

 

[vlaiv]

1 minute ago, jetstream said:

I'm not so sure that a another slab, pored around the pier (with rebar drilled and epoxied into it) on top of the other would provide what he needs. Even using bonding compound on the pier (or roughed up and "buttered") would most likely not give the wanted stability.

 

Why do you think that?

Here is what I'm contemplating at the moment. Not sure if it is good solution - but it is an idea.

I'm sure we can work out pros and cons of it.

Idea would be to add x4 L brackets with anchors to fixate pier to base and then pour one "step" of pyramid around it? Something like this:

I know that you think pouring it in one go is best way to do it - but I don't really see how that can be done at this stage unless I bring down whole structure and redo it again?

[vlaiv]

Alternative is to smash the pier itself - making sure at least some rebar is left sticking out of the base. Then another set of rebar is welded to those bits and another pouring is done - this time with preparation and adhesive.

Maybe even special concrete mix should be used to avoid shrinkage.

[UKDiver]

1 hour ago, Franklin said:

It's totally fixable, just need some plywood for the form work and another load of concrete.

Exactly how the Kuala Lumpur Monorail was fixed.

[Franklin]

20 minutes ago, vlaiv said:

What we have here is failed cold joint.

What you have is 3/4 ton of concrete hanging onto your pad by a thread. It needs reinforcing at the base with extra ballast (more concrete). They would have PVA'd it but I doubt it would have made much difference. I don't think it's structurally viable, as is. It's too high and heavy for an 8"x8" base. Even if it wasn't moving now it would as soon as you put a mount and scope on it. I don't know what else to say, maybe get a structural engineer to take a look at it. I've worked on house builds for years and I think they're all still standing.🤣

[jetstream]

46 minutes ago, vlaiv said:

Here is what I'm contemplating at the moment.

Doing this will be the best solution of repair IMHO. Use "anchor bolts, (actually studs) in drilled holes and epoxied. I would then drill the pier and epoxy rebar in there or maybe better bolt some angle iron to it extending past a foot or so. Yes the angle would be better.

How thick is the existing slab? it has footings?

[vlaiv]

Here is an update.

Not sure what I'm going to do - but I'm not going to keep that pier that is poured at the moment.

While showing the problem to main builder - he proposed that we do - exactly as I proposed above - to anchor pier and pour additional segment on concrete.

Then I complained about the finish of edges and asked if there might be air pockets inside or anything - and I managed to separate chunk of pier about 5-6 inches long and 2 inches wide with my hand (maybe I'm exceptionally strong and not being aware of it - moving pier, crumbling concrete - single handed ).

Thing is crumbling on its own. I absolutely have no idea what could have happened to cause all of this - but anything further is no go until I figure out good solution and find people capable of doing it.

One solution would be to do steel pier. I looked up and I have easy access to square pipe 6mm walls 200mm side.

I can also have base plate 10mm steel cut to size and make triangular supports out of same material.

Only problem would be anchoring it to the base of the pier. I'm thinking pouring sort of thin slab of concrete - 10cm with rebar and epoxy thingy to hold it glued to base with M16 threaded rods sticking out of it so I can bolt down pier base?

[skybadger]

Clear the pillar and replace with steel column ?

I can't see any guarantee of bonding to a new pour here but I guess high rise builders do that all the time too. 

My 12" diameter pier is 6' long and sits on a square plate bolted to the foundation block by resin fixed  inserts. 

[Ricochet]

12 minutes ago, vlaiv said:

thin slab of concrete - 10cm

This sounds way too thin. How deep does the existing pier foundation go? If deep enough I would be more inclined to drill down into the existing foundation and epoxy long rods into it to bolt a steel pier to. 

[vlaiv]

29 minutes ago, Ricochet said:

This sounds way too thin. How deep does the existing pier foundation go? If deep enough I would be more inclined to drill down into the existing foundation and epoxy long rods into it to bolt a steel pier to. 

I think it goes at least 80cm but closer to 1m.

That sounds like a good idea. Not sure if it's going to be doable without wrecking the observing deck first as there is not much room beneath it to comfortably work. I guess smaller person could get under it and operate drill, although length of drill + drill bit could be an issue?

Will look into that option - but yes, it sounds good.

[UKDiver]

7 minutes ago, vlaiv said:

I think it goes at least 80cm but closer to 1m.

That sounds like a good idea. Not sure if it's going to be doable without wrecking the observing deck first as there is not much room beneath it to comfortably work. I guess smaller person could get under it and operate drill, although length of drill + drill bit could be an issue?

Will look into that option - but yes, it sounds good.

It looks like you have about 80cm between the floors, that should be ample for drilling etc. It's not as if you need to swing a pickaxe or hammer to break a hole. The pier will obviously crumble with little help. A steel pier and steel bolted down base will be a better job. Might have to weld the pier to the base in place as I doubt it will go through the hole from underneath without breaking out the hole some.

Your builder owes you big time for the hassle.

[Franklin]

2 hours ago, vlaiv said:

Thing is crumbling on its own.

If the pier concrete is crumbling like that, did they use the same mix/methods for the deck? None of it looks safe or effective to me. Why didn't they install joist hangers when building the blockwork and just fit 7"x2" joists. A bit of studwork and a nice hardwood floating floor would have been ideal. That deck/pad appears to be the same thickness of a block (20cm) and at approx. 2 sq m (judging from photo), that's a lot of weight to be supporting itself, even if they did put reinforcing mesh panels in the mix. It's nearly a cubic metre of concrete resting on three walls. Maybe I'm unaware of building tecniques in Serbia.

Edited November 21, 2021 by Franklin
spelling

[Ricochet]

2 hours ago, vlaiv said:

length of drill + drill bit could be an issue?

So long as you have enough room start the hole with a good sds drill and short drill bit, you can then drop longer drill bits into the hole, connect the drill and continue drilling. However, with the cramped conditions the drilling will be difficult. Your builders will probably have to take it in turns drilling.

[UKDiver]

Franklin makes an excellent point the concrete quality elsewhere in their constructions. Worth a very good look for other crumbling concrete if they used the same batch for other jobs.

[jetstream]

4 hours ago, vlaiv said:

One solution would be to do steel pier

👍

Weld a 1/2" thick maybe 14"x14" to the steel tube and then anchor bolt the plate to the concrete floor where the old pier used to be. Welding the plate on the tube under the floor no big deal. I use a Fronius Transpocket 180 for such things.

[vlaiv]

I think that piece that fell off had air pocket issues and as far as I can tell from discussion - they were not quite gentle when separating wooden mould from concrete.

Rest of the structure does seem solid and good enough. Observing deck is 10cm and it looks 20 because there is cross beam underneath it.

I'll post some better images tomorrow.

[vlaiv]

1 hour ago, jetstream said:

👍

Weld a 1/2" thick maybe 14"x14" to the steel tube and then anchor bolt the plate to the concrete floor where the old pier used to be. Welding the plate on the tube under the floor no big deal. I use a Fronius Transpocket 180 for such things.

I think I'm currently preferring this solution.

20x20cm square pipe - 6mm thick walls and 10mm base plate that will be at least 50-60cm on a side. I'll add some 10mm fins as well - probably to the corners of steel pipe.

From what I'm reading 8"x8" might be a bit small for that height - but that is what I have readily available without actually building/welding pier myself from steel sheets.

I was offered hollow / lattice type steel pier as alternative - something like this:

What do you think about that approach?

 

[900SL]

There's some bad advice in this thread.  I'm a Chartered Structural Engineer. Cantilever rule of thumb is height/depth < 10, so a 8" pier should be fine. 

From your later posts the concrete is clearly defective. If you want any professional advice or help drop me a PM

 

Edited November 21, 2021 by 900SL

[vlaiv]

1 minute ago, 900SL said:

There's some bad advice in this thread.  I'm a Chartered Structural Engineer. Cantilever rule of thumb is height/depth < 10, so a 8" pier should be fine. 

 

What criteria is that based upon. Is it just structural stability / load bearing capability?

People that advocate larger "diameter" (or side in square case) of pier often consider minimal deflection at usual wind loads. I don't have a first clue of how I would calculate such a thing, but I guess you probably can.

If I have square pipe with side 20cm that is 1.6m high and wall thickness is 6mm - what would be angle of deflection if wind of say 6m/s blew perpendicularly on 60cm x 30cm OTA cross section?

I personally think that pier is not the weak link and that scope / mount connection is weak point, or maybe there is some "elasticity" in the mount that will respond to this wind load - like backlash or whatever, but for sake of argument - can we calculate deflection of the top of the pier if everything else is rigid?

[900SL]

Deflection of tip loaded cantilever = PL3/3EI

P=load, L=length cubed, E=Young's modulus, I = moment of inertia. I'll let you know tomorrow when I have access to section inertia calculator