Screw in an aluminium sheet

[Robert_spider]

I have some screws going inside an aluminium sheet of 3mm
Though the screw are four in square pattern (2+2)
They are connecting a bracket of cctv.

The weight is 5kg only
I just want to calculate the the pullout force
The maximum pull out force at which the screw will get pullout from sheet
The screw is 5mm dia and 40 mm long.
One correction they are M5 screw with nut at the back.
Is there a particular formula by which I can calculate the maximum force for pull out of a single screw

 

[rb1957]

nuts and washers, yes ?

so the fastener fails either by stripping the thread in the nut, or by pulling the washer thru the sheet ... both pretty high numbers compared to the expected load (< 100 lbs per ?).

probably the critical failure mode depends on how the sheet is attached to the building.

I'd call this "passed by review". Or maybe run a simple test with a resonably conservative load.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Robert_spider]

Yes,
There is 3mm Aluminum cladding.


The 4 M5(5mm x40mm) are going in the cladding with nut at the back of aluminum cladding, they are saying it machine screws.

I am new in this field, the force critical here is created by turning, so it will be a pull out force.
Is there any empirical formula which I can put and get maximum pull out capacity against 3mm aluminum sheet.
So, I can compare with my actual load.

With regards to the nuts and washer
The nut is there and it is also not common nut it is like cylindrical nut, Sorry I don't know proper terminologies.

There is no washer as far as I can see
But there is mechanism of the CCTV provider like a small thin plate is there where four screws will go, this will connect to cladding so we can assume that there is an individual washer.

 

[NorthCivil]

where are you located?

your profile says IE (ireland?)

if so, the governing standard will be EN 1999.1.1.2007 I believe.

Not 100% sure on this as i have never practiced in europe. but i have referenced this eurocode standard in my location as the aluminium design standard from my country is a bit limited in some ways, the eurocode is more developed than my local standard for some applications.

 

[jjl317]

In the US, aluminum design is addressed in the ADM (Aluminum Design Manual), which in the 2010 versions (latest I have in front of me) addresses connections in Chapter J. Based on what you described, there could be several potential checks that could be appropriate, including pullover and pullout.

 

[MotorCity]

Although not directly applicable, AISI has equations that directly calculate the pull out and pull over capacities of a screw in sheet metal, but its for steel. Maybe start there as a rough estimate and use the properties for aluminum sheet.

 

[Robert_spider]

This Euro Code 9 Was helpful.

Anyone here from Facade Industry?
I am stuck in another problem now and it is related with Transom Connection With Mullion Justification.

 

[drawoh]

ghilman,

Design codes are not my department. This is being noted above.

I have done lots of sheet metal design. Metal sheets and plates are not rigid. If your screws are load bearing, such as a cantilevered mount, they should be right next to or incorporated into a gusset or bent edge.

--
JHG

 

[rb1957]

buttt ... you don't have self-tapping screws ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Robert_spider]

Yes they are screw, pardon for my English.
They are self tapping m5 screws
Which are getting bolted

Also there is a sheet which will be there on top of the 3mm cladding
So the screw goes in the sheet then the aluminium sheet, then it gets bolted also at back.

 

[rb1957]

? why would you "bolt" a self-tapping screw ? Are you adding the nut as a "jam nut" to help ensure the fastener stays where you put it ?

If you're using a nut, the strength of the self tap is negligible ... it'd be better IMHO to drill a plain hole for the fastener and to install the nut as retention.

I think it's very easy to over torque a self-tapping screw and so strip the hole thread.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Robert_spider]

This is the screw they are saying it machine screw except the length is 40mm, yes the nut is there

 

[rb1957]

those don't look like self tapping screws.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.