Framing connection question
Framing connection question
(OP)
I'm designing a connection between two light guage steel framing members. The connection will need to withstand a load of 3100lb. I'm looking to use teks fasteners if possible. Otherwise 1/4-20 hex bolts. Need to determine number required and configuration. My question is: when designing for such a connection, must allowable screw loads be met or is it ok to move towards the ultimate screw loads. Big difference between the two. Two 12-14 teks would be enough using ultimate loads whereas I would need atleast 5 considering allowable loads.






RE: Framing connection question
RE: Framing connection question
RE: Framing connection question
Typical safety of factor is four (4) if the manufacturer is showing the "ultimate" values. It would be up your engineering judgement on what safety factor you are willing to use.
RE: Framing connection question
For shear, some references require a safety factor of at least 3 (ASCE 8).
I would use a safety factor of at least 4 and then check interaction (shear/tension) as well.
RE: Framing connection question
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Framing connection question
I have never quite understood why they always summarily put a factor of safety of 4 or even 5 on these fasteners for anchorage. I can understand if there is a large coefficient of variation, but sometimes the manufacturer gives the standard deviation and the coefficient of variation is usually less than 10%. For a normal distribution, they say 4 standard deviations away from the mean has practically a zero percent chance of occurrence. With a factor of safety of 4 and a coefficient of variation of 10%, even if you assume your nominal strength is 4 standard deviations away from the mean, you will still have a factor of safety greater than 2.
I don't get it. Perhaps, they are worried about improper installation, which is a valid concern, I suppose.
RE: Framing connection question
I agree that as Mike stated if it is a question of a couple of extra connectors, then that is a small price to pay. Just thought I would share that discussion with everyone.
JWB
RE: Framing connection question
Yes, I agree. I haven't found screw capacities to generally be a problem. My comment was more geared towards something like the capacities given for mechanical anchors into masonry. I'm always having a hard time making that stuff work and its frustrating because it is due to these very high safety factors.
RE: Framing connection question
RE: Framing connection question
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Framing connection question
RE: Framing connection question
what exactly do you mean by a 20% failure rate? 20% failed for the design loads? or 20% failed to reach ultimate capacity?
RE: Framing connection question
unfortunately hindsight is a b*tch, I had hoped they would be installed by the steel erector or a carpenter. Maybe we need to create a trade.
Abusementpark,
We were testing to working load. I wasn't there so I can't say what the reasons are/were. We had a few different anchors on site, am yet to see the breakdown of failures.
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it