Light Guage Screw Connection Calculations 1

[rgerk]

I am currently engaged in projects requiring engineering calculations for self-drilling screw connections into light gauge steel. The connections are currently being designed for uplift (tension) and shear loads. The 2001 AISI design manual does a great job explaining the different capacity modes for shear and tension, howeever, it falls short of explaining how tension and shear interact.

Currently, we calculate the tension and shear capacities separately and then apply a unity equation. (T/Ta)^(5/3 + (V/Va)^5/3 <= 1.0. This equation seems to make sense, but I was wanting further input from other designers.

Are there any good references or rules of thumb for treating combined tension and shear loads.

Thanks.

 

[rb1957]

i use (T/Ta)^2+(S/Sa)^2 = 1,
bruhn uses (T/Ta)^3+(S/Sa)^2 = 1 (but this is much harder to work with, and my expression is conservative).

 

[civilperson]

The larger the exponent, the less conservative the combined values become. The expression inside the the parenthesis is less than unity so raising it to a higher power makes it smaller. The elliptical interaction curve which is the basis for the equations may be approximated as three straight lines as shown in Manual of Steel Construction LRFD Third Edition, page 16.1-244.

 

[UcfSE]

The 2004 supplement to the 2001 NASPEC from the AISI has an interaction equation for screws in section E4.5.

 

[rgerk]

UcfSE,

I don't follow your info. Can you point me to the website link that you saw or post the interaction equation? The only supplement I see is for the "Prescriptive Method, one and two family dwellings" for $9.00. Is this what you are referring to. Thanks.

 

[UcfSE]

2004 Supp. to the 2001 NASPEC by AISI

Note this comes in an electronic version (SG05-1e) and a printed version (SG05-1p) and costs $25.00 either way.