Testing of the metal purlins

[masona]

This is the letter from the independent structural engineer regarding the weight of the solar panels on the club roof.

Following our initial visit earlier in the year we have recommended undertaking some material testing of the metal purlins to establish their strength grade. To do this we will need to take some small samples of the roof purlins.

How do they take a small samples of the purlins?

How is it tested?

I thought the Z Purlins size is enough for the weight calculation unless they are looking into it deeper?

 

[Paulg31]

The testing will be to determine the grade of steel. For example with hot rolled steel sections you commonly get grades S275 and S355. I'm not sure what the common grades are for cold rolled sections. They relate to the tensile strength of the material and hence will affect the load capacity in bending.

 

[masona]

The testing will be to determine the grade of steel. For example with hot rolled steel sections you commonly get grades S275 and S355. I'm not sure what the common grades are for cold rolled sections. They relate to the tensile strength of the material and hence will affect the load capacity in bending.

They want to drill 2 x 25mm dia hole in 2 locations, would this not weaken the Z-purlin?

 

[RonnyRaygun]

They want to drill 2 x 25mm dia hole in 2 locations, would this not weaken the Z-purlin?

The holes can be drilled in specific locations that should not affect the ability of the purlins to carry the current load. i.e. away from the centre (maximum bending) and away from the ends (maximum shear).

Having said that, it seems overkill to test the material strength unless the purlins are already on the limit of capacity. Have the SE done calcs based on the dimensions of the purlin and a minimal steel grade (say S235). If they are within capacity then there's no problem.

 

[tony1851]

Yes, wondered about that; maybe they just want to spin the work out for a bigger fee??

 

[masona]

They want to drill 2 x 25mm dia hole in 2 locations, would this not weaken the Z-purlin?

The holes can be drilled in specific locations that should not affect the ability of the purlins to carry the current load. i.e. away from the centre (maximum bending) and away from the ends (maximum shear).

Having said that, it seems overkill to test the material strength unless the purlins are already on the limit of capacity. Have the SE done calcs based on the dimensions of the purlin and a minimal steel grade (say S235). If they are within capacity then there's no problem.

This is from the tenant independent structural engineer.

There is a deflection on the roof with 207 solar panels resting on with 640 concrete slabs, our structural engineer report is completely difference to the solar panels installer structural engineer report therefore the tenant who own the solar panels have got their structural engineer to investigate

 

[Paulg31]

I wouldn't worry much about the two holes. I guess they'll put each hole in a different purlin and they'll avoid areas of high moment and shear as stated above.

So is there excessive visible deflection which has led to this investigation?

 

[masona]

So is there excessive visible deflection which has led to this investigation?

//www.diynot.com/forums/building-regs-planning/snow-load-calculation.408750/

 

[Paulg31]

Ok now I understand.

It'll be interesting to hear the test results.

As before even considering the high deflections currently I don't think you'll have any problems with the two 25 mm holes as long as they're placed suitable places.