cold formed screwed connections

[zahzoo]

I've found more than a few screw capacity tables based on the AISI '96 spec.

All note that a 3.0 safety factor is already incorporated in the table, then another footnote states:

"The nominal strength of the screw must be at least 3.75 times the allowable loads."

This is kind of vague, and I don't have a copy of the AISI spec. Could someone give me an interpretation of this?

Should I multiply my load by 3.75 before I use the table? A 3.0 safety factor is already there. Do they mean one screw or all the screws added togather?

 

[LowLax]

I'm looking at the SSMA book, and I think the critical loads in the tables are based on the steel studs yielding not the screws. I think the 3.75 is just saying the screw itself needs to have that factor of safety. I've never checked that though.

 

[UcfSE]

Check the 2001 AISI spec instead in chapter E. You will find equations for nominal strength of screws for different thicknesses of steel, tensile strength, and screw diameter. The values for the screw itself are based on published manufacturer results and/or testing. The factor of safety used is 3.0. There are several tables available from different manufacturers. I'm surprised you found one that gives you allowable loads since most I have read are ultimate strengths. Manufacturers typically recommend a FS of 3 to 4. What kind of allowables are you coming up with? You should compare those with others and with calculated values to give you a better picture of what you are reading and to help make a good judgment about what value to use.

 

[whyun]

You may also compare the allowable values to the design values listed in ICC Reports for various manufacturers using tested values. Note that the footnotes in the tables typically state that the factor of safety is 2.5