Self-Drilling Fasteners 2

[dik]

I have a new project where the client is using self-drilling fasteners to secure framing. The attachment is 3/16 material to 12 Ga. There are 4 fasteners per attachment. The loads are strictly shear and the untimate load per fastener is 2100lbs. There's no recommendation of a FOS, and I was thinking of 3, and using this as the limit load (this still has DL and LL load factors) because there are multiple fasteners for each connection. Anyone have any thoughts on the approach. Is it too conservative? I don't do a lot of work using self-drilling fasteners.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[NorthCivil]

more of my work is in the world of screws rather than the world of bolts.

your original post sounds fine, except a shear value of 2100lbs for a screw? might want to re-check that number.

I never assume more than 200MPa for screw strength, it might be a tad conservative, but most shops arent buying high end screws from lichtenstein, they are buying them in bulk in big buckets that have passed through a few hands and had a few different brochures describing them,[pre][/pre] on their way out of the chinese factory.

 

[dik]

From TEKS 3 Catalogue... and used a FOS = 3 for resistant load Vr = 700lbs. Applied loading has DL and LL factors on it... for FOS approx 4... only ITW TEKS 3 permitted... no subs... Is there another table that is more appropriate?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[NorthCivil]

Hi Dik, sorry i was thinking in limit states rather than allowable stress. 700lbs is a bit high for my gut... contractor may use screws other than the fancy ones sold by TEKS. depending on how safety critical your application is, maybe you want to allow 4x for FOS?

when self drilling thick material like 12g steel, there may be screw fatiguing, broken shanks, overtorqued screws, funny fits.. some failed screws the installers will notice, some they will not. screws dont slip on nice and neat like bolts. I always layer on the safety factors nice and heavy, and even then add a few more than i need if there is room.

 

[Tomfh]

I agree, be generous. 4 TEKs carrying the weight of a car feels a touch light.

Make sure the plate bearing, pull out and tear out are ok too.

 

[dik]

I agree... but checked against bearing and tearout, and was surprised... 12 ga is like 1/10" thick... other than incidentals, the load is nearly pure shear; there is no tension... that's what prompted the use of a 'FOS' of 3... 700 lbs for a limit states load looked a little more realistic.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Just received pop rivet catalogue with load information... we'll take a gander at pop rivets, too... last time I used them... I don't recall if I checked for tearout... I was dealing with 'real' steel sizes. I do remember the difficulty in obtaining load data. Only thing more difficult was getting the weight of a 'box of beer' on a Friday afternoon... try to get someone think that you're serious...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik