Good evening, i wonder if anyone can help please, i have to produce a Method Statement for the demolition of a Pre Stressesed Concrete Slab, (Porte Cochure), if that is the right spelling. I have had a site visit with a company who specialises in the decomissioning of such structures, but they are merely going to give advice as to what the risks are. This structure is in 3 sections, two end slabs abutting other buildings and the main centre span being Pre Stressed concrete, the two end sections merely reinforced concrete, it is my intention to have a crash decking erected to the underside of either end and manually demolish these, then use excavators to pulvarise the centrepre stressed section piecemeal fashion, thus removing the concrete and taking pressure off of the stress bars, prior to mechanically cutting through them. Any information would be a great help!

RayRapp has a very good point so please address it and about your site visit; are U picking brains or are they going to price etc. the work?

'Manually demolish' does that mean the use of jack hammers & similar if so where is your HAVS management?

There's more to it than just 'prestressed'. The method to adopt depends upon the form of construction - is it pre-tensioned or post-tensioned? If post-, are the ducts grouted? What condition are the bars / strands? What condition are the anchorages (if any)?

There's a lot of energy in a prestressing bar - you really don't want to let one go. I know of a bridge over a railway where a transverse bar anchorage failed - the bar fired itself out the side of the bridge (through some concrete on the way) and a couple of hundred yards up the track - I think it was half inch diameter or three-quarters, and was three or four metres long. That was an early segmental structure and the transverse bars were not grouted, but someone needs to know if that applies to your structure.

In my opinion, you should not be producing a method statement for this - a structural engineer that does this kind of work should be producing a method statement. You really do need a specialist.

Well, from your latest response, the information you're getting so far seems correct (exploratory works required, condition of structure is critical, risk of the whole thing going off like a bomb etc). I would expect a structural engineer to be more likley to be correct about these matters than a member of IOSH, to be honest (though there is obviously some overlap in those sets).

But the real question seems to be bigger than just how to deal with a prestressed slab - how do you know that the information is correct is an issue of competence assessment of the parties involved. It's a duty under CDM that parties check their own competence, and a duty on the client to check the competence of all appointees.

I return to my previous statement - in is my strongly held opinion that you should not prepare a method statement for this - the structural engineer or the demolition contractor should prepare a method statement for this. Why would you tell the specialists how to do their specialism?

I advise that U listen to 'achrn' and others as this is a *specialist area noting that sometimes a highly hazardous operation has to take place irrespective of other factors and that is what H&S management is all about e.g. Adapting to a given environment to progress a business whist doing what we can for the employees e.g. exposing staff to HAVS when cutting out the concrete may be the lesser of 2 evils in this case

*Specialists include both structural engineers & similar inclusive of the demolishion people involved as they all need to be appropriately competent not just experts in demolishing standard houses!

Best of luck