Extending pillars

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Extending pillars

Postby ratsima » Fri Feb 05, 2010 6:38 am

Any guidance appreciated.
We are extending our house in Bangkok. The original house has a very, very sound structure (and over 20 years). The addition involves extending the upper floor by 2m to existing support pillars. (The house is 2 storey except for a 2m strip along the back of the house (width 8m) - we are extending over that strip). As I say above the foundation strength of the existing pillars is not in doubt, although we are still using lightweight materials throughout.

We have used the same builder for a few years for various projects and are very comfortable with his approach to building, he is cautious and thoughtful about the work he does, well aware we do things a certain way cos we have two kids.

The pillars have to be extended upwards. This is where my concerns arise. I had assumed the existing concrete pillasr would be stripped back a bit to reveal the rebar and the rebar from the new pillar sections tied to that, all to be encased in concrete. A bit heavier but surely essential?

The builder has other ideas and has put up one pillar for our review. It is a standard square section steel beam/pillar with a welded square plate which he has affixed to the head of the existing pillar with two bolts, set into the existing pillar. The overall framework of the extension was always intended to be metal but seeing the pillar affixed by only two bolts has given me some real concerns. Even the weld of the plate to the square section beam seems a bit too lightweight for my thinking. NB there are 4 such pillars to be extended upwards, along the back of the house: corner, at 3m, then a further 2m, then the final corner after another 3m.

The builder fairly points out that the new structure will have strength overall and I accept that to a degree. There will also be other points where existing and extension meet and will be pinned together at these points. He also says that this method of extending a pillar upwards is fairly common in Thailand.

Building has stopped while this issue is resolved. I cant get it out of my head that the slightest dunt could shear the bolts. Anybody got any thoughts on this, it would be so much appreciated.
Is the builder's steel plate/beam affixed to the head of the existing pillar OK? OK, but should have more bolts? If not OK, how should it be done?

Many thanks
ratsima
 
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Re: Extending pillars

Postby geordie » Fri Feb 05, 2010 7:04 am

Not too mutch to work with here what size are the bolts how far from the edge of the concrete are they
what do you expect to apply the lateral force required to shear the bolts
Do not underestimate the amount of force requierd to shear a bolt it sounds from your description the force is downwards anyway so the bolts are purely to prevent slipping any chance of a sketch or picture
how is he linking the posts together you could if you are unhappy insist that he exposes the rebar and weld a plate to it you are the client and its your money and safety you are dealing with
take a look at what they use to fix curtain walling on an office block gravity is the main anchor
for half a ton sheets of walling/glass
If you are not comfortable with what he has proposed INSIST more bolts more welds or bigger bolts
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: Extending pillars

Postby ratsima » Fri Feb 05, 2010 8:22 am

Geordie, info much appreciated. My basic question was about the technique he was using to extend the pillar and from your answer it seems this method of affixing a pillar with welded plate to the top of the concrete pillar with bolts is OK, in principle. The steel pillar is 4"x4" (3.2mm) and the plate is 6x6. I'm waiting for full spec on the bolts and the other elements involved in the building of the extension.

On the good side, the builder is pretty relaxed about doing what we want. He assembled the first pillar for us to review and decide if we wanted changes, so he's not trying to force it through. He has already offered to do what you suggested by welding the rebar to the plate instead of/in addition to bolts.

Geordie I appreciate you taking the time to respond even without much tech detail in my request. I will post more of the detail as I get it and additional comments are very welcome.
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Re: Extending pillars

Postby geordie » Fri Feb 05, 2010 5:25 pm

Ratsima you are looking at the wrong place for a failure the bolts as i said earlier will take a lot of force to shear a manufactures spec would suprise you what i personally would be looking at is how close to the outside edge of the colum are the fixings and what sort of fixings he is using Please do a google search on resin fixings and chemical fixings a rawlbolt type anchor or a plug type anchor relies on exerting outward force on the material you are fixing into these fixings can either crack the material on instalation or later rust a resin fixing is efectivly you glue the bolt into place so no stress onto the pillars and the bonus is it seals the hole so no rust and its available over there in the big diy stores near paint/mastic is the place to look if you cannot find it car body filler is pretty mutch the same a simple test is fix one post conventional one resin and see which one pulls out at two meters its a good lever i would put my money on the resin surviving better make sure if using it blow all the dust out of the hole
first a pepsi bottle will do the job
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: Extending pillars

Postby MangoPin » Fri Feb 05, 2010 7:36 pm

Hi,
Here is my advice for what its worth. I can well see your concern. If your european/american/austrailian builder suggested something like this in Europe I guess you would accept it without questioning. Should be the same here but even if you know and trust your builder it may not feel the same.

In general I agree with all that Geordie says

As I have been told, a correct weld is seldom the weakest point of a metal construction. Next the anchoring of the plate should be done using chemical anchor resin I guess.

I put a number of radio masts for the swedish embassies before, now they are all taken down in favor of this new internet fad. Tears come to my eyes.
Anyway these 6 or 9 meter aluminum masts were bolted to a concrete foundation using chemical anchors. This is how we did it.

Drill 4 holes 20 cm down about 6 mm larger than the threaded stainless irons to be put later. Blow out all the dust. Put two glass ampouls with the 2-comp epoxi resin in a hole. Fix the threaded iron to a slow speed drill. Push down the iron to break the glass ampouls and drill the iron slowly down the hole. This will bring the iron down and at the same time mix the 2-comp epoxi. After a few seconds the resin will react, the iron will fix to it and you will break your hands if you dont stop the drill. If this felt good, do the remaining 3 bolts.

Later we could climb these masts without any worries. Those were the days.

I see e.g. Sika has these ampouls. Probably many other brands available also.

Wish you good luck. Dont forget to tell us how it turned out.

MangoPin
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Re: Extending pillars

Postby geordie » Fri Feb 05, 2010 8:03 pm

mangopin glad too see someone else that has used the stuff with satisfaction with my work we always used the two part rather than the liquid ampules but only because the concrete was so ropey that there was a risk of the resin liquid disapearing down a void with the paste you twist by hand for penitration and can buy plastic cages for if you have a void always drilling the hole 2-3 mm larger than the stud/bolt that you use setting was 20 mins to 2hrs depending on temperature also age of resin old resin could go off before you got the stud in no big deal drill it out and put new stuff in fantastic strength though
my comments may be wrong but never deliberately
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Re: Extending pillars

Postby ratsima » Sat Feb 06, 2010 6:04 am

The builder has decided to abandon the bolts idea and suggests welding the rebar in the existing pillars to the 6"x6" (6mm) plate supporting the new metal pillar. He told us that the weld between plate and pillar yesterday was a temporary weld just so we could see the pillar "in place" but of course he didn't tell us that. I thought it was just a crap welding job.

I think going to accept the new plan to weld the rebar to the plate, rather than pursue the option of convincing him to use the chemical/resin/epoxy adhesive solution with bolts. The anchor fixing bolts he had used anyway for that first pillar (he gave me a sample of what he used, look just like Rawlbolts) seem woefully short, about 5cm (not at all like MangoPins suggestion of a 20cm depth for the fixings!). Is the weld of the rebar to the plate a valid solution? Do I have to ensure that the rebar goes through holes in the plate to be welded to the top surface of the plate? Or should I stick to "my" guns and demand a resin/epoxy fixing type solution? What size of anchor bolt would you say?

I'm still fairly impressed with the builder's keenness to solve this problem - he isn't just trying to force any solution through. One problem is - as ever - communication. He just doesn't seem to be able to tell us (what I regard as) important information unless we stumble over the issue in a protracted Q&A session! Secondly, the Thai wife seems unable to translate what I say or he says without trying to interpret what we mean and translating that rather than what we actually said. Sometimes her interpretation is the exact opposite! So I have to understand - as much as I can - everything said in Thai, thereby usually adding my misunderstandings to the mix! In practice, it's a lot less Keystone Cops than that but boy do site meetings take a huge amount of time and much scratching of heads. It's quite funny after I calm down!!!

So thanks again Geordie and MangoPin for your advice, it's much appreciated. if you have time, what do you think to the weld solution rather than the resin/epoxy fixing?
ratsima
 
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Re: Extending pillars

Postby geordie » Sat Feb 06, 2010 9:10 am

welding to the rebar is a satisfactory solution as long as its a good quality weld with a decent penetration on the weld also that the rebar is ok 10 mm or upwards the chemfix as you will of seen from my comments to mangopin are a great engineering solution but not somthing that the average thai would ever come across or even the average diy enthusiast but once you have used it you swear by it even soft breeze can take a fixing with it the great news is that it does not rely on putting stress on the material to achieve a fixing unlike a rawlbolt its waterproof so will stop the fixing rusting away also acts as a shock absorber on machinery likely to vibrate loose a normal fixing if you take a look at the CHANGNOI build there are some plates with 4 holes punched in them for the tops of columbs your builder could use similar i personally would have the rebar through the plate for welding then weld the extensions on top

alternately you could try and source the resin fixing it simple enough the stuff over there is in what looks like a paint tin its a two part resin the hardener has to be mixed into it once this is mixed you fill the hole as best you can with the resin the hole should be at least 2 mm larger
than the stud 10 mm stud 12 mm hole when you have resined the hole turn the stud as you push it into the hole this is to guarantee it gets into the thread an all little crevices the thing is once you have used it and shown the builder how simple it is to use you will have a new best friend the store i saw the stuff in was in pattaya large diy store home mart i think
if you cannot find it let him weld and maybe a couple of bolts as well belt and braces
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: Extending pillars

Postby ratsima » Mon Mar 08, 2010 6:58 pm

Well, it's been a couple of weeks when some deep thinking has been required. Because we simply cannot prove the strength or spec of the existing piles and pillars we think it might be a bit reckless to go ahead with an upper live-in extension. I appreciate the input from the posters, esp Geordie but that decision has now been made. We are going ahead with a separate but linked "above the driveway extension" with all new piles (9 x 6m clusters) and pillars.

What to do now with the part of the house we were going to extend previously? I am considering a balcony built of wooden materials, so it would be more like a deck I suppose. Metal pillars and metal beams used as the structure, using a suspended floor with wooden beams. The builder is in shock at the thought of a wooden deck, must be concrete and ceramic tiles he says. But I have seen quite a few wooden decks around Bangkok, tho not built partly above living space as we plan ie the wooden deck would extend out over the kitchen, downstairs toilet and part of the dining room. The deck fence would be standard square section metal, welded in 1m - 1.2m vertical uprights, with a metal railing at top and bottom. Again, it all has to be lightweight. The whole deck surface will be open with absolutely nowhere for water to gather, rain should not be a major issue surely if joints, bonds and varnishes are maintained properly. Between deck and walls of the house we will use aluminium flashing.

Anyone got any idea if the wooden deck is doable, using a suspended wooden floor with wood beams? Any suggestions of how to do it, tips and traps? We would plan to go to architectural recycle shops to get older flooring and beams with natural resistance to pests and water and use that. Or get pre-treated timber to meet the same resistance objectives.

If the wooden deck is not doable or with too many risks, any other ideas for a really lightweight solution? NB whereas we don't plan to be hosting parties for lots of people on the deck, tho lightweight it will still be very strong. It will not be flimsy in any way.

As ever I really appreciate the input. I also realise that this may have gone out of the remit of the "concrete" forum but I have posted here for continuity. Thanks again.
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