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Rick Warner  
#1 Posted : 07 July 2011 18:14:44(UTC)
Rank: Forum user
Rick Warner

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  
#2 Posted : 07 July 2011 20:28:00(UTC)
Rank: Super forum user
RayRapp

Rick Not sure what assistance you are looking for? Surely, the person planning and writing the MS should be someone experienced in this type of demolition, such as, an engineer? Ray
bob youel  
#3 Posted : 08 July 2011 07:52:00(UTC)
Rank: Super forum user
bob youel

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?
Judex  
#4 Posted : 09 July 2011 08:31:04(UTC)
Rank: Forum user
Judex

The method statement for demolishing normally is the reverse steps taken during the construction phase of the building with all safety measures. Some aspects to take into consideration are: mobile crane(s) to support existing part of slab(s) while diamond cutting if this is the method to remove the topping concrete and underneath pre-stressed slabs normally of about 2.4 m width; guardrails at edge; supporting props underneath the slab while removing; MEWP to fixed anchor bolts / bars cutting at ends for pre-stressed beam while support by mobile crane(s). These might avoid dislodging the adjacent structures. Have views and supports of structural engineer(s) as mentioned by RayRapp to determine the sequences and determine the different load / shears / moments (sagging , etc) both for slabs and beams at each steps to ensure safe demolition. Information, Toolbox talks prior to start work every day, supervision, and appropriate PPE
achrn  
#5 Posted : 11 July 2011 08:15:44(UTC)
Rank: Super forum user
achrn

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.
Rick Warner  
#6 Posted : 11 July 2011 09:26:22(UTC)
Rank: Forum user
Rick Warner

I have attended a site meeting with a Structural Engineer, he is preparing Risk Assessments etc for me. Our client is currently in the process of carrying out exploritory works, to ascertain if the ducts are grouted and what condition the bars/strands and anchorages are in. My concerns are that the Structural Engineer has informed us that even with precautions in place, there is still a possibility that this thing will go off and the outcome could be catastrophic. This was my reasoning for contacting members of IOSH, i am still being expected to prepare a demolition Method Statement for these works, the contents of which will include the findings and information received from the structural engineer, being as i do not specialise in this field, how am i supposed to know if the information which i am receiving is correct?
achrn  
#7 Posted : 11 July 2011 10:12:59(UTC)
Rank: Super forum user
achrn

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?
RayRapp  
#8 Posted : 11 July 2011 10:20:40(UTC)
Rank: Super forum user
RayRapp

'...how am i supposed to know if the information which i am receiving is correct?' Apart from the obvious checks of competency of the engineer providing the advice...you can't and don't know if the information is correct. I have signed off as checked and approved more method statements than I care to remember which have been written experts in their field ie engineers. All the more reason an expert should write the method statement you describe me thinks. I personally would not write a MS unless I was very comfortable with the scope of work/methodology. It's a tricky situation, granted, but I feel h&s practitioners must not go beyond a certain comfort zone. If things do go wrong there could be a lot of questions to answer...
bob youel  
#9 Posted : 11 July 2011 10:24:44(UTC)
Rank: Super forum user
bob youel

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
Rick Warner  
#10 Posted : 11 July 2011 17:54:04(UTC)
Rank: Forum user
Rick Warner

All your comments are as i thought, that is why i am a member of IOSH and asked for my fellow Professionals to comment, thankyou so much, i will print this page and pass it under the nose of my employer, along with my letter, depicting my reluctance to prepare a Method Statement and Risk Assessments for a project that they have priced and secured, but one which i want no part of. Thankyou all once again!
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