Structural engineer question. Fixing in concrete.

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Dan_Veluwe
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Post by Dan_Veluwe »

Since my plot borders on a forest and the neighbor who owns it is deaf for my requests to clear semi dead trees,
I have to build 'falling trees proof' . So it can not be the standard whimsy DIY pack of fire wood with steelpanel roof.

I decided to build an all steel beams and girders construction CARPORT that can withstand a tree falling on it. :ugeek:

A friend has a company that specializes in custom buildups on large trucks. He makes a set that I can bolt together.

I choose concrete slabs [ 2,5 m x 1 m x 0,12m each 789Kg ] as pavement. This is instant foundation for the carport.

Question :
Fixing the columns [ steel footplates welded to the columns ] with bolts to the concrete slabs, what is the best choice ?
There are 'glue anchors' : drill a whole, put a glue cartridge in and push a threaded rod in. When set you tighten the nuts.
Also expansion anchors, in iron, zinc plated or rust proof steel....

Who has professional experience with this kind of fixings ? It will all get wet regularly... :roll:
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Lunar
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Post by Lunar »

Hi Dan,

As with most things nowadays there is too much information out there once you start looking.

You may want to have a browse around this site to get to grips with the basic choices... https://www.hilti.co.uk/c/CLS_FASTENER_7135

I think you might have general issues with a concrete pad thickness of only 120mm.

Most expansion fixings of the size you will need for a tree resistant structure require a greater substrate thickness (bolt depth) than 120mm - and the same applies to chem-fix type fixings, which are only for blind holes and the holes need to be thoroughly cleaned of dust first - being careful not to clog up the vacuum cleaner in the process!

I would recommend building the structure inside the edge of the concrete pads, thereby ensuring that the fixings are not too close to the pad edge. You may also want to consider using a plated stud type fixing where the bolt is passed through a decent size and thickness plate and then through the concrete pad from the rear, so forming a compression type fixing on the faces of the concrete. With no data to go on I would suggest using metal plates of the same footprint and thickness as the foot plates on the bottom of the columns. Considering the weight of a decent tree, the impact load - even if cushioned by lots of springy branches - could range significantly (also summer to winter), so I'm guessing the foot plates are being drilled for M16 fixings? If so make sure the holes are at least 20mm if you want any chance of all 4 corner foot fixings lining up.

However the size of pad you quote is effing heavy (to use a technical term), so you will need to plan how to insert such fixings from behind - best done prior to pad placement but then you need very accurate hole measuring and pad placing.

Having said all that, to put things into perspective I had a large silver birch (circa 60cm at base) fall in my garden a few years ago - whilst it smashed a recently bought granite table (about 7m away from the tree) into crazy paving, it didn't demolish a 2m high brick garden wall. My strongly built decking also survived unscathed other than the fact that the steel tube garden chair legs were driven right through it! I got a call at work about the tree fall and we'd been sat at the table with neighbours only the afternoon before - yikes.

Please take all the above as advice and experience only, as I am not a structural engineer - I work for an elevator company as a modernisations technical and process manager, so have seen some "interesting" examples of building work in my time, and come up with potential solutions that then need to be worked through and proven before being implemented.

Hope this helps some - and of course we will want to see photos - or a time-lapse maybe! :)

EDIT:
Looking at the Hilti technical data sheets you will really be on the cusp if using M16 fixings, but if they are M12 you may well be ok to use a sleeve / wedge anchor. I would recommend asking for advice from there agent near you - if you prepare a sketch of what your situation is they will be able to identify the correct type, size and depth of fixing to use and save you a lot of time looking into it.
M12 may sound small but if you have a set of 4 on each base plate - and considering the impact force from a tree is generally downwards anyway - then you'd be surprised at how much force they can take.
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Dan_Veluwe
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Post by Dan_Veluwe »

@Lunar___ Wow.. ..thanks for the details ! But I already found out the maximum I can get is M12, since I can only use 100mm hole depth.

As you say, expansion may be tricky, though the slabs come with substantial rebar. I was planning to stay away 250mm from the edge
of the plate, also way into the rebar area. So I think the expansion anchors will not shatter the plate.

Plate is 2500 mm x 1000 mm x 120 mm ..

rebar.jpg

The construction exists of 6 columns with sq. 160 x 160 x 4 mm footplates with 80 x 80 x 4mm columns and the same headplate size.
These will be around 3500 mm apart in a 3x 2 rows pattern with 80 x 60 x 3 mm box profiles girders on top, this bolted together with
M12 rfs bolts, 4 each per headplate. Footplate 4 M12 D13 holes on 140 x 140 mm square.

The compression type fixing you suggest is too much for me. The slabs are 800Kg each and very level, I am not messing with these.

I imagine that elevators are another level (sic) of structure since you deal with vibrations and floorslabs can be accessed from below.

I looked at some testing of 'pulling out' anchors and 4 x 12mm is way stronger then the 4mm footplate can take : the weld will tear before
the anchors are pulled out completely. They could move out a bit, depending from which corner the three comes.

But the question was : do I go for glued, expansion or the latest type 'screw-in' that work just like woodscrews.. :shock:

W- BS Wurth :

I think the time-lapse is a bit much, but the result I can post with pictures, maybe also after a tree fell on it... :roll:

This will be my 'vault' to keep my F-Type and F-Pace since bascily we live in a space - in - the - woods..
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Lunar
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Post by Lunar »

Looks like you have things pretty well organised there.
Screw-in looks good - Wuerth have a good product reputation - and they depict your type of fixation arrangement too, although I’ve not seen any independent tests or comparisons with chemical or expansion fixings.
Chemical are slower to use and a bit messy - they also need time to fully set and achieve strength so best not done on a windy day.
With expansion or sleeve anchor you want to look for the type you can insert through the foot plate for ease of installation.
Also compare costs of the 3 types - chemical are probably quite a bit more expensive for no obvious benefit.
As you are some way in from the edge, and inside the rebar grid, I’d probably go for a traditional anchor With a 19mm ratchet socket to speed up installation - although those screw-in ones look interesting :)
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Post by Dan_Veluwe »

I've been sourcing info on the screws. Seems they are mostly for dry conditions and indoor, so I fail to understand why they
apply them outdoors in the video's . I need 24 anchors, and I guess acrylic with simple threaded rods are cheapest.

But the expansion anchors that are 'hammered' in and subsequential tensioned , look the easiest if the 'screws' are indeed
not specced for outdoor use..

Thanks for thinking along !
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Dan_Veluwe
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Post by Dan_Veluwe »

@Lunar_ Almost forgot I promised to post..

I bought a concrete drill. Just didn't realise it had an 'in stroke' and 'out stroke'. So by setting the drill depth limiter I set it
on the 'in stroke' resulting in perforating the slab in some places. You should have seen my face when I cleaned the wholes
with compressed air and the dust came out of the neigbouring hole... :lol:

We first blindly started pushing glue in, but stopped after halve a cartridge.. .. next day I reamed the holes and when I cleaned
them the leak was blocked by the overdose in glue.

This is how the parts arrived : made to specs and zincplated:

IMG_20200516_185615971_HDR.jpg

As a part of the complete overhaul of our rear garden, I choose to use concrete slabs as unitary paving.
Its a perfect foundation for the carport, put in place with a vacuumsuction device on a crane :

IMG_20200516_213318148.jpg

The frame is erected, all pieces less then 18 Kg ;

IMG_20200520_200856951_HDR.jpg

Footings done with Fischer treaded bolts, glued in place . These will be surrounded by a brick ornamental footing:

IMG_20200520_171421813.jpg

..and a wooden cover to make it look like wooden columns [ these are the real deal ], to stay in keeping with the rest;



.. to be continued..

IMG_20200514_171004587_HDR.jpg

IMG_20200514_171115836.jpg

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Lunar
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Post by Lunar »

That’s going to look pretty awesome once finished - a proper job.

...I like the idea of driving through the car port straight into your hallway even more :D
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Post by Dan_Veluwe »

Thanks, its a lot of work, but its really nice to build something. The solving of detailing and small problems are a good challenge.

Actually, this is the rear : the porch edges on the lounge. In front we have an even smaller version. My first idea was to make a carport
in the historic meaning of " Port Cochère " . Later on I found out that the origin is a passage - tunnel like - through a building courtyard,
with the door to the house in this tunnel. Later this was changed to the platform on pillars in front of the house..

When we build the house in 2007, I wanted to have this in a 7 m x 5 m version. My wife found ti grotesque. But I still regret not doing it.
Some years later the council made it impossible, hence the one on the side of the house now..

Front / entrance porch :

20150923_143008.jpg


This is inside the Port Cochère in the summer palace of the last King of Portugal, in Vila Viçosa , central Portugal. Build as a convent.

IMG_20191031_111850229.jpg

The stables next door : first time 300 horses fitted in one stable in 5 centuries... :mrgreen:

IMG_20191030_174148431.jpg

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Post by Deleted User 1715 »

Looking good, going to be a nice home for the 300 ponies and plenty of space to sit outside and keep an eye on it!
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Dan_Veluwe
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Post by Dan_Veluwe »

GusA wrote: Fri May 29, 2020 5:48 pmLooking good, going to be a nice home for the 300 ponies and plenty of space to sit outside and keep an eye on it!
Thanks ! Actually 550 ponies... a P300 and a 25t F-Pace... 8-)
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