Allowable Compressive Force on Steel Needles Thru Masonry Wall 1

[DavyBeans]

I'm currently working on a job in London involving putting some temporary needles thru a 400mm thick masonry wall. The load on the wall at the temporary needling level is approx 200kN/m.

In the permanent sense building control will allow an allowable compressive force of 0.63N/mm2 under a concentrated load for an existing masonry Wall as per Ciria Report 111.

Is anybody aware of what the allowable compressive force is for masonry bearing on top of a temporary needle? There is no indication of same on any of the current codes available to me.

For a 203UC needle my allowable compressive force will only be (Fc / 203mm x 400mm) = 0.63N/mm2. Fc = 51kN with needles spaced at 1.0m ctrs. My needles would need to be spaced at 255mm ctrs to comply with this rule.

Is a relaxation of this compressive force allowable in the temporary sense? Or is anyone aware of a code which might give suitable guidance for masonry compressive forces on tempoary needles?

Thanks in advance.

 

[hokie66]

I have no knowledge of your codes, but would comment that creating an opening in a wall with that much load normally requires shoring the floors which load the wall in order to build the columns and beam.

 

[csd72]

Davybeans,

I had to look up the ciria guide myself to check.

The 0.63 comes from 0.42 x1.5 (local bearing factor) I assume.

The 1.5 factor is conservative in my opinion and many other codes allow a higher factor to be used for certain situations (The Australian code uses a formula which I believe can be greater than 2).

I would suggest you look at the eurocodes for this one as I would be very surprised if you did not get a much better result.

If this doesnt help then you can always look at the actual brick and mortar type as I am sure that those streeses are based on the worst case of lime mortar and weak bricks.

To be honest, I suspect that this temporary condition is often not checked.

 

[DavyBeans]

Cheers CSD72.
Its taken me some time to get an appropriate answer for this. But you are indeed correct in saying that this temporary condition is not often checked. However for such a large load it may cause the wall to vertically deflect > L/360 and therefore causing cracking in the wall that is being needled. I would prefer to ensure that such a check is satisfactory.

Referring to the old code CP111 the basic compressive stress may be multiplied by 1.5. If the brick taken have a basic compressive stress > 7.0N/mm2 allowable compressive stress on the brick will increase. The mean basic compressive strength for bricks in the London Area is 10-15N/mm2 and therefore an allowable value of 0.63N/mm2 is conservative and should only be used where better information is not available. If an exact value is required the method is to test the compressive strength of 10 bricks and take the mean of this value.

So after some research I think I have found the appropriate answer. But as always any comments are welcome.
Cheers.
DavyBeans.