Concrete roof formwork

[CharLou]

back again...

Our underground garage is now close to getting a new steel reinforced concrete roof. The roof is 10.5 x 7.5 mtrs. 175mm thick.

Because its an underground structure the SE has specified we use 4 RSJ's along the 7.5M width at 2M centres which are now in place and will act to support the concrete. RSJ's 254x254x7.75/107Kg.

My question is about the best way to create our formwork which we'll use to pour the concrete on to. Because of the RSJ's and two internal walls there's no way to use a conventional formwork deck, so we have to come up with something ourselves.

The SE hasn't offered any practical advice in terms of formwork, other than suggesting a 4"x2" lattice and acro arrangement.

I was planning to cover the whole area with 25mm Chipboard and make the lattice work below as suggested, but the concern is that we can't have the chipboard sitting between the concrete and RSJ's. We could potentially cut a section of chipboard directly above the RSJ's, but this solution isn't ideal.

Can anyone offer the benefit of their experience?
Thanks

[rxbren]

might sound a bit harsh but...........
if you don't know how to do it get someone in to do it

[lutonlagerlout]

sounds like a job for a shuttering firm mate
if you get it wrong there will be a lot of tears and concrete on the floor
I can visualise what you are trying to achieve but when approx 30 tonnes of concrete goes on to it any weakness will be exposed in a bad way

seen it happen,then the fire brigade had to come out to wash the cement away
cost a lot of money
LLL

[GB_Groundworks]

My shuttering company do a design for me a d then provide a dressing and everything I need leeda Acrow part of the a plant group I'd be getting the pros on as if you get your rebar wrong or for work or your pour you'll loose a lot of money

Reinforced concrete is a specialist trade and not one for diy'er

Easy to kill someone under 30 tons of concrete roof

[seanandruby]

What about com floor. You place ot on top of your rsj's and concrete over it
The metal inderside is visible and is there for life. You can concrete with light agg to tefuce the weight of concrete. Other than thst you can use doka, or gass shuttering.

[CharLou]

Sorry, I dont think I exlained myelf well in my original post. I'm not doing this work, I'm just after ideas as to how we can accomplish this. I had some ideas of my own, but as I've not done this previously I'm looking to call upon the experts for help.

Ideas like Com Floor is what I'm after, but I'll also ask a shuttering firm to take a look.

Thanks for posting.

[GB_Groundworks]

Again not diy though fusion welder to do the studs and edges

But works well we've done lots of slabs on it kingspan k deck is another name for it

[lutonlagerlout]

charlou if you were a little bit more local i would have the perfect man to put you right but he is working on waterloo station right now
the experts you need on this are experience steel fixers and shutterers who can come and price and do the form work

obviously the most important thing is that the concrete when placed has no chance of causing the formwork to fail

saw this happen in a lift shaft on a shopping centre and they ended up with 4 m3 at the bottom of the shaft,and that was lads who supposedly knew what they were doing

LLL

[CharLou]

Thanks for all the advice so far.

Just had a Formwork firm take a look. They're going to send me a quote in the next day or so.

They said the easiest thing is to install '4x2' joists under the RSJ top rib and fix ply to the top. Where the end walls don't have any RSJ to fix the joists to they would need to add a beam against the block work and attach a few acrows. I was expecting them to say the joists also needed supporting but surprisingly they said there's not enough weight.

[rxbren]

Make sure you get a few quotes the ideal people you want are type of guys who do the concrete crossovers on roadways

[lutonlagerlout]

char if they are insured for this it sounds like a plan
I make it around 14m3 =33 tonnes of concrete
that is a fair wallop in mine and most peoples minds

has the engineer asked for the steel to be encased or just firelined afterwards?

LLL